Wheel And Tire Faq

[Sadistic]

Due to the recent topics of runflats, tires, and rims I decided I would go through and lay down the basics for everyone to use a guide to help them make better choices on tires, and wheels.

In my opinion the first thing that anyone should learn about tires, is how to read the sidewall of a tire. Here lies the vital information of the tire. Anything you need to know about the tire itself is placed on the side, for easy access. Here are some of the things that your sidewall will include:

P225/55/R16 89H - This series of numbers is the size, load and speed rating of your tire. The first letter "P" indicates that this tire is Passenger car tire. Next is 225/55/R16. In all "P" tires, these numbers mean the same thing. The first number or in this case "225" is the width of the tread and is measured in Millimeters. The next number, or "55" is the Aspect Ration, or Sidewall height. This is always a percentage of the first number. So in this case, this tire would be 55% as tall, as 225 Millimeters is wide. Next up is R16. The R stands for Radial tire, and 16 is the size of the wheel that this tire is to be installed on, and is measured in Inches. So in a nutsheel what it comes down to is P225(mm)/55(% of 225)/R16"

The next set of numbers is the load rating of the tire. In this case it would be "89," which is an assigned number that corresponds with the load-carrying capacity of a tire. Most passenger car tire load indexes range from around 75 to 100. What this means is that if each tire on our car is the same, each tire can carry a max of 1,279 lbs. Combining all four tires together nets us 5,116 lbs of total weight capacity that these tires can hold before they are under extreme duress, and are more than likely to explode, or rupture. These really isn't a big deal on cars.

This is mainly a concern on smaller trucks, and larger Vans that use "P metric" tires, and have to be cautious of how much weight or cargo they can haul. This number is also figured by the amount of air pressure in a tire. The figure of 1,279 lbs is based on MAX tire pressure. Your vehicle does not require you have the max amount of air in a tire. That creates uneven, and premature wear to your tire. If you over inflate your tire past the vehicle's specifications, the inner tread of your tire will wear faster than the outside edge. There is a small plaque or plate on the inside of your door, or under the hood. Always check for your vehicle's air pressure there.

After the load rating, comes the speed rating. First I'd like to say, that this in no way measures the performance of the tire. This number is only for speed and heat. It is used to measure how much speed/heat this tire can take before it is no longer certified. This doesn't mean that a tire with a lower speed rating can't go above that, just that the tire shouldn't be taken above that. This is where excess heat will start to damage the tire, tread can seperate, tires can explode. There are many things that can go wrong. With that said, lets get down to what exactly "H" means. Years ago the highest speed rating a tire could achieve was "ZR" or "Z." This was because tires of high performance nature were made with unstable compounds and couldn't be measured above a certain level. Tires that were tested had failed at certain speeds, and some made it to higher. So "Z" was rated at 150 mph and above. Now with the technological advances with rubber compounds and tread design we now have "W" and "Y." These are actually the highest a tire can achieve now, and are no longer broad range. Here is a small chart to show ratings and their top speed.

(Rating --------------- Speed in MPH)

B ----------------- 31 P ----------------- 93

C ----------------- 37 Q ----------------- 99

D ----------------- 40 R ----------------- 106

E ----------------- 43 S ----------------- 112

F ----------------- 50 T ----------------- 118

G ----------------- 56 U ----------------- 124

J ------------------ 62 H ----------------- 130

K ----------------- 68 V ------------------ 150

L ----------------- 75 W ----------------- 169

M ---------------- 81 Y ------------------ 188

N ----------------- 87 Z ------------------ Over 150

Treadwear 220 - Next is the Treadwear rating. The number 220 actually has no value. It is based on a test that is run on a test road track somewhere in the lower west of the US, and is only used for comparison. It's a means to determine the life of a tire under normal circumstances. It's to be assumed, that a tire with a 220 treadwear, will be worn down faster than a tire with 500. This number usually does give a good understand of how soft the compound of the tire is. If any of you have ever riden in a car with a "High mileage warranty," You know what I mean. Those are tires that usually have a 500 or above treadwear rating, and are extremely hard. That's how they get their long life. The softer the tire, the faster it will wear down from normal driving. There is no chart that says a 220 will last so many miles, that's all determined by climate, road conditions, and driving. I would suggest finding a good medium, on a passenger car tire 350 is a good round number, not too hard, not too soft and will probably net you a good 30,000 miles. If you want Ultra Performance, the lower, the better.

Traction A - This is pretty much self explanatory. This is the rating of traction that your tire can achieve, against other tires. This can be anywhere from D all the way to AA or AAA. A racing slick at optimum temperature would probably be AAAA. (This isn't a real rating, but using it to explain.) A street slick would be AAA. Your Ultra High performance tire would be AA, and Max Performance A. The chart goes down from there. This is what you want to look for to judge Performance of the tire. A tire with an AA is going to perform better than a tire with a B.

Temperature A - This goes along the same rating as Traction from above. This measures the amount of heat the tire can handle under driving conditions.

Max Pressure 35 PSI - This is the max tire pressure that the tire can hold before it can rupture under weight. If you were to put 40 psi of air into this tire and drive, your tire would buldge and become junk very quickly.

Sidewall 2 plies 2XXXXX Cord - This is Tire ply composition and materials used. Has very little bearing on you. More for manufacturer Standards.

Well, that is the sidewall of your tire. Always inspect the sidewall and make yourself familiar with what it says. It's always best to be well informed and know when something may happen, then not know and be put into a dangerous situation. Your tires are your stability, they can make or break you within a moments notice.

---------------

The Dreaded Runflats - First I want to start off by saying that Runflats aren't such a bad thing. When put on the right car, or right situation they can actually be quite convient, but like any other convience you must pay a price. And that price would be sacrificing handling and ride quality. The basic idea behind Runflats is simple. When they make runflats, they add many plys of rubber to the sidewall of the tire. This adds an EXTREME amount of rigidity to the tire. The basic principle is this. If the sidewall is thicker, it can hold more weight, as the air in your tire begins to expell due to a puncture, the rubber can actually withstand the weight of the car and be driven so many miles to get you to saftey, or the comfort of the nearest Tire shop. They list Runflats at being able to be driven 55 mph for 50 miles at max with zero air pressure. This is because the tire is still made of rubber and is going to start to shred at some point because of the rim. Because of all this extra rigidity in the tire, it's going to react to the road very differently than other tires that would only have 3 plys instead of 9. First, the sidewall can't flex when turning so the car is going to act very twitchy. Along with that, when going over bumps the tire isn't going to absorb any of the shock a regular passenger tire would, so you lose quite a bit of ride quality, and your car now feels like a lumber truck, instead of the gorgeous Lexus it once was, or should be. So that is basically a quick summary of Runflats.

---------------

Fix-A-Flat - Can tire sealants are another one of those convient things that were created, but like Runflats, there is a price to pay and could be large. Here's what happens when you spray those into your tire. You spray it into your tire, because of rushing air out of the puncture, the air moves the fluid into the hole and begins to seal. The instant you spray the fix-a-flat into your tire, it begins to eat away at the inside. It's almost acts like acid to the inside of your tire. Another thing you have to deal with now until you get the tire fixed is you have this liquid sloshing around in your tire, so it is no longer in balance and you get to deal with that for the rest of your trip. I don't know if any of you guys have actually seen a tire that has had Fix-A-Flat used in it once it's been pulled off the rim. It basically makes the inside of your tire into soup, and makes a huge mess. This can also lead to your tire becoming un-repairable. So if you do have to use a can of this, make sure and get the tire fixed immediately. That way you might be able to stem/patch the tire, instead of purchasing a new one.

----------------

The next thing I want to cover is approved rim widths for size tires. This is one of the most common mistakes that people make when buying tires and wheels. They want to maximize rubber contact on the road, but don't want to pay the extra money for a wider rim, so they stuff a big tire onto a small rim, and this causes a few things to happen. One, the tire is under extreme duress at all times and can tear very easily. Two, the tire can come off the bead (which holds the wheel to the rim) and you can end up damaging the wheel, and your car from the tire shredding. So it is always good to understand what tires will fit on what rims. A wheel's width is measured from the inside front lip, to the inside of the rear lip. Not the total rim's width. Here is chart that you can use as a quick reference:

50 Series tires and above (215/*50-75*/)

(mm) = (Rim width)

215 = 6" - 7 1/2"

225 = 6" - 8"

235 = 6 1/2" - 8 1/2"

245 = 6 1/2" - 8 1/2"

255 = 7" - 9"

265 = 7 1/2" - 9 1/2"

275 = 7 1/2" - 9 1/2"

285 = 8" - 10"

35-45 Series tires (215/*35-45*/)

(mm) = (Rim Width)

215 = 7" - 8 1/2"

225 = 7 1/2" - 9"

235 = 8" - 9 1/2"

245 = 8" - 9 1/2"

255 = 8 1/2" - 10"

265 = 9" - 10"

275 = 9" - 11"

285 = 9 1/2" - 11"

295 = 10" - 12"

--------------

Rotation of Tires - I am one of those people that is a firm believer in rotating your tires on a regular basis. After working with tires for so long I have come to see what can happen to tires if they aren't rotated. I have seen tires that have 50-60,000 mile tread warranties gone within a matter of 15,000 miles. The best time to rotate your tires is when you do your oil change. It takes an extra few minutes, and can save the life of your tires dramatically. In a front wheel drive car you move the front tires straight back, and criss-cross the back tires to the front. (Left rear to the Right front) RWD and AWD vehicles should be done just the opposite. Rear tires go straight foward, and criss-cross the fronts to the rear. I understand that in some vehicles this can't be done, due to having directional tires. In that case, move the front tires straight back, and the rear tires straight foward. Even doing this little bit will save you from prematurally wearing out the front tires due to more weight on them while driving and cornering.

--------------

One of the most important things that people have to deal with when purchasing wheels and tires, is what size to buy? I'm sure most of you know that your speedometer runs off your tires. They are calibrated from the factory to the factory sized tires. But, what happens when you put larger tires on your car? Does your speedometer become inaccurate? It can, but doesn't have to. When you take into account all the size factors of a tire, you can find the overall tire diameter. This is one easy way to go with different sized tires, but keep your speedometer in check. Here is a very simple forumula for you to use:

Lets take 225/55/16 to start with.

First take the section width of the tire (225) and multiple that by 0. the aspect ration, or series. (0.55) Then multiple that by 2. Divide that number by 25.4 and add your rim size. (16)

This is how it would look on paper.

225 X 0.55 X 2 = 247.5/25.4 = 9.74 + 16 = 25.74 <-- This is your overall tire diameter of a 225/55/16

So lets try to figure out what would be a good size to upgrade to without affecting our speedometer too much.

225/55/16 = 25.74

245/45/17 = 25.68

255/45/17 = 26.03

235/45/18 = 26.36

Alright, so now that we have our overall tire diameters of some tires sizes that we think will work, lets figure out just how much these will change our speedometer.

First take the new overall tire diameter, in this case we'll pick the 235/45/18's at 26.36. Then divide that by your old overall tire diameter, which would be 225/55/16 at 25.74. Next multiple that by MPH, and that will give you what your ACTUAL speed is. So it would look like this..

26.36/25.74 X 55 = 56.32 So when your speedo says 55, you're actually going about 56, which isn't such a big deal. But, your speedometer works on an exponential scale, so the further from 55 it goes, the farther off it will be. If you did the same thing for 100 mph it would be about 102 mph in actuality. Now this is with a very small margin, but think of a car going from 195/65/14 to 245/55/17

195/65/14 = 23.98

245/55/17 = 27.61

55 mph would actually be 63 mph

100 mph would actually be 115 mph

So it can add up, so be careful on what tires you choose to go with.

------------

Well guys and gals, I think that pretty much sums up the basics of purchasing wheels and tires. Just remember when buying wheels, always make sure they will fit your bolt pattern, have the right offset, and will clear any aftermarket Calipers or Rotors you might have, or be looking to buy. If anyone has any questions, go ahead and post them or send me a PM and I'll try to answer them as best I can.

Thanks for the space LOC!

-Sadistic

[AWJ]

Looks great my man. I'm going to bump this over to the wheel tire forum. May we can make it a sticky.

[Matthew_McNally]

May we can make it a sticky.

we certainly can.

great work sadistic!

[ese9537]

May we can make it a sticky.

we certainly can.

great work sadistic!

←

I am new to this forum and a novice tire buyer. Currently I have P225/70R16 101S Goodyear Integrity tires on my Lexus RX300. I find them to be horrible on wet surfaces. Need to replace them and have been told to look at Bridgestone Dueler H/L, Bridgestone Dueler H/L Alenza, Michelin ALT, AWP Uniroyal Loreado or Maxxis. Any suggestions? ese9537

[Lexusfreak]

May we can make it a sticky.

we certainly can.

great work sadistic!

←

I am new to this forum and a novice tire buyer. Currently I have P225/70R16 101S Goodyear Integrity tires on my Lexus RX300. I find them to be horrible on wet surfaces. Need to replace them and have been told to look at Bridgestone Dueler H/L, Bridgestone Dueler H/L Alenza, Michelin ALT, AWP Uniroyal Loreado or Maxxis. Any suggestions? ese9537

←

Yokohama Geolander G-051's, Michelin Cross Terrains, or the brand new Toyo Open Country H/T which all come in your size. B) Excellent all round performers, but the Michelin will be by far the most expensive.

[ivanfromtheuk]

May we can make it a sticky.

we certainly can.

great work sadistic!

←

I am new to this forum and a novice tire buyer. Currently I have P225/70R16 101S Goodyear Integrity tires on my Lexus RX300. I find them to be horrible on wet surfaces. Need to replace them and have been told to look at Bridgestone Dueler H/L, Bridgestone Dueler H/L Alenza, Michelin ALT, AWP Uniroyal Loreado or Maxxis. Any suggestions? ese9537

←

Yokohama Geolander G-051's, Michelin Cross Terrains, or the brand new Toyo Open Country H/T which all come in your size. B) Excellent all round performers, but the Michelin will be by far the most expensive.

←

i dont know if you guys get pirrelli in the US but they make my aristo stick to the road like glue... great for cornering.... make sure you get the 95V rated tyres though....

by the way, I need some info or recommendations from you guys about body kits, etc....

cheers all

[Huskers]

Hello, Great post! I do have one question pertaining to upgraded rims. I have a 98 es with 15" rims and want to upgrade to 16". I have the opportunity to buy rims from a 2003 gs300. From what I have found out everything would work the only question I have is about the offset. It is 50 for these rims but I do not know what offset would work with my car.

Thank you very much!

[Aikibro]

Great stuff Sadistic...very informative!

[SOMEONE ELSE'S GOT MY NAME]

Great stuff Sadistic...very informative!

One thing missing on Sadistic's charts: Rolling resistence. Though ALL manufactures document what compounds do what to the mileage, they seem to want to guard the facts like they're some kind of national secret. Most Lexus owners only go ape for handling/ride I'd imagine . . . but on the RX-400h ~ we're wanting to give that factor high marks.

There IS a web site out there that documents all the manufactures on one chart ... rating the traction composite ... treadwear ... performance, as WELL as Rolling resistence. Bridgestone has one model that beaats the other brands, so I'm inclined to go that rout.

Thanks for the thread ... an oldie but a goodie!

[jhm555]

Sadistic

I am new to the forum and just bought a 2001 LS430. This car has 255/40R19 98Y's on the front and 255/40R-19XL 100Y's on the rear.

Could you tell me my actual speed when the speedometer reads 65?

Also they are, of course, very responsive but pretty firm. Is there any thing I can do to soften and quiet the ride apart from getting new rims?

[VMC]

Due to the recent topics of runflats, tires, and rims I decided I would go through and lay down the basics for everyone to use a guide to help them make better choices on tires, and wheels.

In my opinion the first thing that anyone should learn about tires, is how to read the sidewall of a tire. Here lies the vital information of the tire. Anything you need to know about the tire itself is placed on the side, for easy access. Here are some of the things that your sidewall will include:

P225/55/R16 89H - This series of numbers is the size, load and speed rating of your tire. The first letter "P" indicates that this tire is Passenger car tire. Next is 225/55/R16. In all "P" tires, these numbers mean the same thing. The first number or in this case "225" is the width of the tread and is measured in Millimeters. The next number, or "55" is the Aspect Ration, or Sidewall height. This is always a percentage of the first number. So in this case, this tire would be 55% as tall, as 225 Millimeters is wide. Next up is R16. The R stands for Radial tire, and 16 is the size of the wheel that this tire is to be installed on, and is measured in Inches. So in a nutsheel what it comes down to is P225(mm)/55(% of 225)/R16"

The next set of numbers is the load rating of the tire. In this case it would be "89," which is an assigned number that corresponds with the load-carrying capacity of a tire. Most passenger car tire load indexes range from around 75 to 100. What this means is that if each tire on our car is the same, each tire can carry a max of 1,279 lbs. Combining all four tires together nets us 5,116 lbs of total weight capacity that these tires can hold before they are under extreme duress, and are more than likely to explode, or rupture. These really isn't a big deal on cars.

This is mainly a concern on smaller trucks, and larger Vans that use "P metric" tires, and have to be cautious of how much weight or cargo they can haul. This number is also figured by the amount of air pressure in a tire. The figure of 1,279 lbs is based on MAX tire pressure. Your vehicle does not require you have the max amount of air in a tire. That creates uneven, and premature wear to your tire. If you over inflate your tire past the vehicle's specifications, the inner tread of your tire will wear faster than the outside edge. There is a small plaque or plate on the inside of your door, or under the hood. Always check for your vehicle's air pressure there.

After the load rating, comes the speed rating. First I'd like to say, that this in no way measures the performance of the tire. This number is only for speed and heat. It is used to measure how much speed/heat this tire can take before it is no longer certified. This doesn't mean that a tire with a lower speed rating can't go above that, just that the tire shouldn't be taken above that. This is where excess heat will start to damage the tire, tread can seperate, tires can explode. There are many things that can go wrong. With that said, lets get down to what exactly "H" means. Years ago the highest speed rating a tire could achieve was "ZR" or "Z." This was because tires of high performance nature were made with unstable compounds and couldn't be measured above a certain level. Tires that were tested had failed at certain speeds, and some made it to higher. So "Z" was rated at 150 mph and above. Now with the technological advances with rubber compounds and tread design we now have "W" and "Y." These are actually the highest a tire can achieve now, and are no longer broad range. Here is a small chart to show ratings and their top speed.

(Rating --------------- Speed in MPH)

B ----------------- 31 P ----------------- 93

C ----------------- 37 Q ----------------- 99

D ----------------- 40 R ----------------- 106

E ----------------- 43 S ----------------- 112

F ----------------- 50 T ----------------- 118

G ----------------- 56 U ----------------- 124

J ------------------ 62 H ----------------- 130

K ----------------- 68 V ------------------ 150

L ----------------- 75 W ----------------- 169

M ---------------- 81 Y ------------------ 188

N ----------------- 87 Z ------------------ Over 150

Treadwear 220 - Next is the Treadwear rating. The number 220 actually has no value. It is based on a test that is run on a test road track somewhere in the lower west of the US, and is only used for comparison. It's a means to determine the life of a tire under normal circumstances. It's to be assumed, that a tire with a 220 treadwear, will be worn down faster than a tire with 500. This number usually does give a good understand of how soft the compound of the tire is. If any of you have ever riden in a car with a "High mileage warranty," You know what I mean. Those are tires that usually have a 500 or above treadwear rating, and are extremely hard. That's how they get their long life. The softer the tire, the faster it will wear down from normal driving. There is no chart that says a 220 will last so many miles, that's all determined by climate, road conditions, and driving. I would suggest finding a good medium, on a passenger car tire 350 is a good round number, not too hard, not too soft and will probably net you a good 30,000 miles. If you want Ultra Performance, the lower, the better.

Traction A - This is pretty much self explanatory. This is the rating of traction that your tire can achieve, against other tires. This can be anywhere from D all the way to AA or AAA. A racing slick at optimum temperature would probably be AAAA. (This isn't a real rating, but using it to explain.) A street slick would be AAA. Your Ultra High performance tire would be AA, and Max Performance A. The chart goes down from there. This is what you want to look for to judge Performance of the tire. A tire with an AA is going to perform better than a tire with a B.

Temperature A - This goes along the same rating as Traction from above. This measures the amount of heat the tire can handle under driving conditions.

Max Pressure 35 PSI - This is the max tire pressure that the tire can hold before it can rupture under weight. If you were to put 40 psi of air into this tire and drive, your tire would buldge and become junk very quickly.

Sidewall 2 plies 2XXXXX Cord - This is Tire ply composition and materials used. Has very little bearing on you. More for manufacturer Standards.

Well, that is the sidewall of your tire. Always inspect the sidewall and make yourself familiar with what it says. It's always best to be well informed and know when something may happen, then not know and be put into a dangerous situation. Your tires are your stability, they can make or break you within a moments notice.

---------------

The Dreaded Runflats - First I want to start off by saying that Runflats aren't such a bad thing. When put on the right car, or right situation they can actually be quite convient, but like any other convience you must pay a price. And that price would be sacrificing handling and ride quality. The basic idea behind Runflats is simple. When they make runflats, they add many plys of rubber to the sidewall of the tire. This adds an EXTREME amount of rigidity to the tire. The basic principle is this. If the sidewall is thicker, it can hold more weight, as the air in your tire begins to expell due to a puncture, the rubber can actually withstand the weight of the car and be driven so many miles to get you to saftey, or the comfort of the nearest Tire shop. They list Runflats at being able to be driven 55 mph for 50 miles at max with zero air pressure. This is because the tire is still made of rubber and is going to start to shred at some point because of the rim. Because of all this extra rigidity in the tire, it's going to react to the road very differently than other tires that would only have 3 plys instead of 9. First, the sidewall can't flex when turning so the car is going to act very twitchy. Along with that, when going over bumps the tire isn't going to absorb any of the shock a regular passenger tire would, so you lose quite a bit of ride quality, and your car now feels like a lumber truck, instead of the gorgeous Lexus it once was, or should be. So that is basically a quick summary of Runflats.

---------------

Fix-A-Flat - Can tire sealants are another one of those convient things that were created, but like Runflats, there is a price to pay and could be large. Here's what happens when you spray those into your tire. You spray it into your tire, because of rushing air out of the puncture, the air moves the fluid into the hole and begins to seal. The instant you spray the fix-a-flat into your tire, it begins to eat away at the inside. It's almost acts like acid to the inside of your tire. Another thing you have to deal with now until you get the tire fixed is you have this liquid sloshing around in your tire, so it is no longer in balance and you get to deal with that for the rest of your trip. I don't know if any of you guys have actually seen a tire that has had Fix-A-Flat used in it once it's been pulled off the rim. It basically makes the inside of your tire into soup, and makes a huge mess. This can also lead to your tire becoming un-repairable. So if you do have to use a can of this, make sure and get the tire fixed immediately. That way you might be able to stem/patch the tire, instead of purchasing a new one.

----------------

The next thing I want to cover is approved rim widths for size tires. This is one of the most common mistakes that people make when buying tires and wheels. They want to maximize rubber contact on the road, but don't want to pay the extra money for a wider rim, so they stuff a big tire onto a small rim, and this causes a few things to happen. One, the tire is under extreme duress at all times and can tear very easily. Two, the tire can come off the bead (which holds the wheel to the rim) and you can end up damaging the wheel, and your car from the tire shredding. So it is always good to understand what tires will fit on what rims. A wheel's width is measured from the inside front lip, to the inside of the rear lip. Not the total rim's width. Here is chart that you can use as a quick reference:

50 Series tires and above (215/*50-75*/)

(mm) = (Rim width)

215 = 6" - 7 1/2"

225 = 6" - 8"

235 = 6 1/2" - 8 1/2"

245 = 6 1/2" - 8 1/2"

255 = 7" - 9"

265 = 7 1/2" - 9 1/2"

275 = 7 1/2" - 9 1/2"

285 = 8" - 10"

35-45 Series tires (215/*35-45*/)

(mm) = (Rim Width)

215 = 7" - 8 1/2"

225 = 7 1/2" - 9"

235 = 8" - 9 1/2"

245 = 8" - 9 1/2"

255 = 8 1/2" - 10"

265 = 9" - 10"

275 = 9" - 11"

285 = 9 1/2" - 11"

295 = 10" - 12"

--------------

Rotation of Tires - I am one of those people that is a firm believer in rotating your tires on a regular basis. After working with tires for so long I have come to see what can happen to tires if they aren't rotated. I have seen tires that have 50-60,000 mile tread warranties gone within a matter of 15,000 miles. The best time to rotate your tires is when you do your oil change. It takes an extra few minutes, and can save the life of your tires dramatically. In a front wheel drive car you move the front tires straight back, and criss-cross the back tires to the front. (Left rear to the Right front) RWD and AWD vehicles should be done just the opposite. Rear tires go straight foward, and criss-cross the fronts to the rear. I understand that in some vehicles this can't be done, due to having directional tires. In that case, move the front tires straight back, and the rear tires straight foward. Even doing this little bit will save you from prematurally wearing out the front tires due to more weight on them while driving and cornering.

--------------

One of the most important things that people have to deal with when purchasing wheels and tires, is what size to buy? I'm sure most of you know that your speedometer runs off your tires. They are calibrated from the factory to the factory sized tires. But, what happens when you put larger tires on your car? Does your speedometer become inaccurate? It can, but doesn't have to. When you take into account all the size factors of a tire, you can find the overall tire diameter. This is one easy way to go with different sized tires, but keep your speedometer in check. Here is a very simple forumula for you to use:

Lets take 225/55/16 to start with.

First take the section width of the tire (225) and multiple that by 0. the aspect ration, or series. (0.55) Then multiple that by 2. Divide that number by 25.4 and add your rim size. (16)

This is how it would look on paper.

225 X 0.55 X 2 = 247.5/25.4 = 9.74 + 16 = 25.74 <-- This is your overall tire diameter of a 225/55/16

So lets try to figure out what would be a good size to upgrade to without affecting our speedometer too much.

225/55/16 = 25.74

245/45/17 = 25.68

255/45/17 = 26.03

235/45/18 = 26.36

Alright, so now that we have our overall tire diameters of some tires sizes that we think will work, lets figure out just how much these will change our speedometer.

First take the new overall tire diameter, in this case we'll pick the 235/45/18's at 26.36. Then divide that by your old overall tire diameter, which would be 225/55/16 at 25.74. Next multiple that by MPH, and that will give you what your ACTUAL speed is. So it would look like this..

26.36/25.74 X 55 = 56.32 So when your speedo says 55, you're actually going about 56, which isn't such a big deal. But, your speedometer works on an exponential scale, so the further from 55 it goes, the farther off it will be. If you did the same thing for 100 mph it would be about 102 mph in actuality. Now this is with a very small margin, but think of a car going from 195/65/14 to 245/55/17

195/65/14 = 23.98

245/55/17 = 27.61

55 mph would actually be 63 mph

100 mph would actually be 115 mph

So it can add up, so be careful on what tires you choose to go with.

------------

Well guys and gals, I think that pretty much sums up the basics of purchasing wheels and tires. Just remember when buying wheels, always make sure they will fit your bolt pattern, have the right offset, and will clear any aftermarket Calipers or Rotors you might have, or be looking to buy. If anyone has any questions, go ahead and post them or send me a PM and I'll try to answer them as best I can.

Thanks for the space LOC!

-Sadistic

[likesthetopdown]

Thanks for the information. I have a SC 430 with run flats and want to replace them with regular tires. Today someone recommended Falken tires that are re inforced. I have never heard of this brand. Any thoughts? I am not happy with the run flats!

[tdub]

Due to the recent topics of runflats, tires, and rims I decided I would go through and lay down the basics for everyone to use a guide to help them make better choices on tires, and wheels.

In my opinion the first thing that anyone should learn about tires, is how to read the sidewall of a tire. Here lies the vital information of the tire. Anything you need to know about the tire itself is placed on the side, for easy access. Here are some of the things that your sidewall will include:

P225/55/R16 89H - This series of numbers is the size, load and speed rating of your tire. The first letter "P" indicates that this tire is Passenger car tire. Next is 225/55/R16. In all "P" tires, these numbers mean the same thing. The first number or in this case "225" is the width of the tread and is measured in Millimeters. The next number, or "55" is the Aspect Ration, or Sidewall height. This is always a percentage of the first number. So in this case, this tire would be 55% as tall, as 225 Millimeters is wide. Next up is R16. The R stands for Radial tire, and 16 is the size of the wheel that this tire is to be installed on, and is measured in Inches. So in a nutsheel what it comes down to is P225(mm)/55(% of 225)/R16"

The next set of numbers is the load rating of the tire. In this case it would be "89," which is an assigned number that corresponds with the load-carrying capacity of a tire. Most passenger car tire load indexes range from around 75 to 100. What this means is that if each tire on our car is the same, each tire can carry a max of 1,279 lbs. Combining all four tires together nets us 5,116 lbs of total weight capacity that these tires can hold before they are under extreme duress, and are more than likely to explode, or rupture. These really isn't a big deal on cars.

This is mainly a concern on smaller trucks, and larger Vans that use "P metric" tires, and have to be cautious of how much weight or cargo they can haul. This number is also figured by the amount of air pressure in a tire. The figure of 1,279 lbs is based on MAX tire pressure. Your vehicle does not require you have the max amount of air in a tire. That creates uneven, and premature wear to your tire. If you over inflate your tire past the vehicle's specifications, the inner tread of your tire will wear faster than the outside edge. There is a small plaque or plate on the inside of your door, or under the hood. Always check for your vehicle's air pressure there.

After the load rating, comes the speed rating. First I'd like to say, that this in no way measures the performance of the tire. This number is only for speed and heat. It is used to measure how much speed/heat this tire can take before it is no longer certified. This doesn't mean that a tire with a lower speed rating can't go above that, just that the tire shouldn't be taken above that. This is where excess heat will start to damage the tire, tread can seperate, tires can explode. There are many things that can go wrong. With that said, lets get down to what exactly "H" means. Years ago the highest speed rating a tire could achieve was "ZR" or "Z." This was because tires of high performance nature were made with unstable compounds and couldn't be measured above a certain level. Tires that were tested had failed at certain speeds, and some made it to higher. So "Z" was rated at 150 mph and above. Now with the technological advances with rubber compounds and tread design we now have "W" and "Y." These are actually the highest a tire can achieve now, and are no longer broad range. Here is a small chart to show ratings and their top speed.

(Rating --------------- Speed in MPH)

B ----------------- 31 P ----------------- 93

C ----------------- 37 Q ----------------- 99

D ----------------- 40 R ----------------- 106

E ----------------- 43 S ----------------- 112

F ----------------- 50 T ----------------- 118

G ----------------- 56 U ----------------- 124

J ------------------ 62 H ----------------- 130

K ----------------- 68 V ------------------ 150

L ----------------- 75 W ----------------- 169

M ---------------- 81 Y ------------------ 188

N ----------------- 87 Z ------------------ Over 150

Treadwear 220 - Next is the Treadwear rating. The number 220 actually has no value. It is based on a test that is run on a test road track somewhere in the lower west of the US, and is only used for comparison. It's a means to determine the life of a tire under normal circumstances. It's to be assumed, that a tire with a 220 treadwear, will be worn down faster than a tire with 500. This number usually does give a good understand of how soft the compound of the tire is. If any of you have ever riden in a car with a "High mileage warranty," You know what I mean. Those are tires that usually have a 500 or above treadwear rating, and are extremely hard. That's how they get their long life. The softer the tire, the faster it will wear down from normal driving. There is no chart that says a 220 will last so many miles, that's all determined by climate, road conditions, and driving. I would suggest finding a good medium, on a passenger car tire 350 is a good round number, not too hard, not too soft and will probably net you a good 30,000 miles. If you want Ultra Performance, the lower, the better.

Traction A - This is pretty much self explanatory. This is the rating of traction that your tire can achieve, against other tires. This can be anywhere from D all the way to AA or AAA. A racing slick at optimum temperature would probably be AAAA. (This isn't a real rating, but using it to explain.) A street slick would be AAA. Your Ultra High performance tire would be AA, and Max Performance A. The chart goes down from there. This is what you want to look for to judge Performance of the tire. A tire with an AA is going to perform better than a tire with a B.

Temperature A - This goes along the same rating as Traction from above. This measures the amount of heat the tire can handle under driving conditions.

Max Pressure 35 PSI - This is the max tire pressure that the tire can hold before it can rupture under weight. If you were to put 40 psi of air into this tire and drive, your tire would buldge and become junk very quickly.

Sidewall 2 plies 2XXXXX Cord - This is Tire ply composition and materials used. Has very little bearing on you. More for manufacturer Standards.

Well, that is the sidewall of your tire. Always inspect the sidewall and make yourself familiar with what it says. It's always best to be well informed and know when something may happen, then not know and be put into a dangerous situation. Your tires are your stability, they can make or break you within a moments notice.

---------------

The Dreaded Runflats - First I want to start off by saying that Runflats aren't such a bad thing. When put on the right car, or right situation they can actually be quite convient, but like any other convience you must pay a price. And that price would be sacrificing handling and ride quality. The basic idea behind Runflats is simple. When they make runflats, they add many plys of rubber to the sidewall of the tire. This adds an EXTREME amount of rigidity to the tire. The basic principle is this. If the sidewall is thicker, it can hold more weight, as the air in your tire begins to expell due to a puncture, the rubber can actually withstand the weight of the car and be driven so many miles to get you to saftey, or the comfort of the nearest Tire shop. They list Runflats at being able to be driven 55 mph for 50 miles at max with zero air pressure. This is because the tire is still made of rubber and is going to start to shred at some point because of the rim. Because of all this extra rigidity in the tire, it's going to react to the road very differently than other tires that would only have 3 plys instead of 9. First, the sidewall can't flex when turning so the car is going to act very twitchy. Along with that, when going over bumps the tire isn't going to absorb any of the shock a regular passenger tire would, so you lose quite a bit of ride quality, and your car now feels like a lumber truck, instead of the gorgeous Lexus it once was, or should be. So that is basically a quick summary of Runflats.

---------------

Fix-A-Flat - Can tire sealants are another one of those convient things that were created, but like Runflats, there is a price to pay and could be large. Here's what happens when you spray those into your tire. You spray it into your tire, because of rushing air out of the puncture, the air moves the fluid into the hole and begins to seal. The instant you spray the fix-a-flat into your tire, it begins to eat away at the inside. It's almost acts like acid to the inside of your tire. Another thing you have to deal with now until you get the tire fixed is you have this liquid sloshing around in your tire, so it is no longer in balance and you get to deal with that for the rest of your trip. I don't know if any of you guys have actually seen a tire that has had Fix-A-Flat used in it once it's been pulled off the rim. It basically makes the inside of your tire into soup, and makes a huge mess. This can also lead to your tire becoming un-repairable. So if you do have to use a can of this, make sure and get the tire fixed immediately. That way you might be able to stem/patch the tire, instead of purchasing a new one.

----------------

The next thing I want to cover is approved rim widths for size tires. This is one of the most common mistakes that people make when buying tires and wheels. They want to maximize rubber contact on the road, but don't want to pay the extra money for a wider rim, so they stuff a big tire onto a small rim, and this causes a few things to happen. One, the tire is under extreme duress at all times and can tear very easily. Two, the tire can come off the bead (which holds the wheel to the rim) and you can end up damaging the wheel, and your car from the tire shredding. So it is always good to understand what tires will fit on what rims. A wheel's width is measured from the inside front lip, to the inside of the rear lip. Not the total rim's width. Here is chart that you can use as a quick reference:

50 Series tires and above (215/*50-75*/)

(mm) = (Rim width)

215 = 6" - 7 1/2"

225 = 6" - 8"

235 = 6 1/2" - 8 1/2"

245 = 6 1/2" - 8 1/2"

255 = 7" - 9"

265 = 7 1/2" - 9 1/2"

275 = 7 1/2" - 9 1/2"

285 = 8" - 10"

35-45 Series tires (215/*35-45*/)

(mm) = (Rim Width)

215 = 7" - 8 1/2"

225 = 7 1/2" - 9"

235 = 8" - 9 1/2"

245 = 8" - 9 1/2"

255 = 8 1/2" - 10"

265 = 9" - 10"

275 = 9" - 11"

285 = 9 1/2" - 11"

295 = 10" - 12"

--------------

Rotation of Tires - I am one of those people that is a firm believer in rotating your tires on a regular basis. After working with tires for so long I have come to see what can happen to tires if they aren't rotated. I have seen tires that have 50-60,000 mile tread warranties gone within a matter of 15,000 miles. The best time to rotate your tires is when you do your oil change. It takes an extra few minutes, and can save the life of your tires dramatically. In a front wheel drive car you move the front tires straight back, and criss-cross the back tires to the front. (Left rear to the Right front) RWD and AWD vehicles should be done just the opposite. Rear tires go straight foward, and criss-cross the fronts to the rear. I understand that in some vehicles this can't be done, due to having directional tires. In that case, move the front tires straight back, and the rear tires straight foward. Even doing this little bit will save you from prematurally wearing out the front tires due to more weight on them while driving and cornering.

--------------

One of the most important things that people have to deal with when purchasing wheels and tires, is what size to buy? I'm sure most of you know that your speedometer runs off your tires. They are calibrated from the factory to the factory sized tires. But, what happens when you put larger tires on your car? Does your speedometer become inaccurate? It can, but doesn't have to. When you take into account all the size factors of a tire, you can find the overall tire diameter. This is one easy way to go with different sized tires, but keep your speedometer in check. Here is a very simple forumula for you to use:

Lets take 225/55/16 to start with.

First take the section width of the tire (225) and multiple that by 0. the aspect ration, or series. (0.55) Then multiple that by 2. Divide that number by 25.4 and add your rim size. (16)

This is how it would look on paper.

225 X 0.55 X 2 = 247.5/25.4 = 9.74 + 16 = 25.74 <-- This is your overall tire diameter of a 225/55/16

So lets try to figure out what would be a good size to upgrade to without affecting our speedometer too much.

225/55/16 = 25.74

245/45/17 = 25.68

255/45/17 = 26.03

235/45/18 = 26.36

Alright, so now that we have our overall tire diameters of some tires sizes that we think will work, lets figure out just how much these will change our speedometer.

First take the new overall tire diameter, in this case we'll pick the 235/45/18's at 26.36. Then divide that by your old overall tire diameter, which would be 225/55/16 at 25.74. Next multiple that by MPH, and that will give you what your ACTUAL speed is. So it would look like this..

26.36/25.74 X 55 = 56.32 So when your speedo says 55, you're actually going about 56, which isn't such a big deal. But, your speedometer works on an exponential scale, so the further from 55 it goes, the farther off it will be. If you did the same thing for 100 mph it would be about 102 mph in actuality. Now this is with a very small margin, but think of a car going from 195/65/14 to 245/55/17

195/65/14 = 23.98

245/55/17 = 27.61

55 mph would actually be 63 mph

100 mph would actually be 115 mph

So it can add up, so be careful on what tires you choose to go with.

------------

Well guys and gals, I think that pretty much sums up the basics of purchasing wheels and tires. Just remember when buying wheels, always make sure they will fit your bolt pattern, have the right offset, and will clear any aftermarket Calipers or Rotors you might have, or be looking to buy. If anyone has any questions, go ahead and post them or send me a PM and I'll try to answer them as best I can.

Thanks for the space LOC!

-Sadistic

Extremely useful information. Thankyou for posting.

[Roger Silvey]

Due to the recent topics of runflats, tires, and rims I decided I would go through and lay down the basics for everyone to use a guide to help them make better choices on tires, and wheels.

In my opinion the first thing that anyone should learn about tires, is how to read the sidewall of a tire. Here lies the vital information of the tire. Anything you need to know about the tire itself is placed on the side, for easy access. Here are some of the things that your sidewall will include:

P225/55/R16 89H - This series of numbers is the size, load and speed rating of your tire. The first letter "P" indicates that this tire is Passenger car tire. Next is 225/55/R16. In all "P" tires, these numbers mean the same thing. The first number or in this case "225" is the width of the tread and is measured in Millimeters. The next number, or "55" is the Aspect Ration, or Sidewall height. This is always a percentage of the first number. So in this case, this tire would be 55% as tall, as 225 Millimeters is wide. Next up is R16. The R stands for Radial tire, and 16 is the size of the wheel that this tire is to be installed on, and is measured in Inches. So in a nutsheel what it comes down to is P225(mm)/55(% of 225)/R16"

The next set of numbers is the load rating of the tire. In this case it would be "89," which is an assigned number that corresponds with the load-carrying capacity of a tire. Most passenger car tire load indexes range from around 75 to 100. What this means is that if each tire on our car is the same, each tire can carry a max of 1,279 lbs. Combining all four tires together nets us 5,116 lbs of total weight capacity that these tires can hold before they are under extreme duress, and are more than likely to explode, or rupture. These really isn't a big deal on cars.

This is mainly a concern on smaller trucks, and larger Vans that use "P metric" tires, and have to be cautious of how much weight or cargo they can haul. This number is also figured by the amount of air pressure in a tire. The figure of 1,279 lbs is based on MAX tire pressure. Your vehicle does not require you have the max amount of air in a tire. That creates uneven, and premature wear to your tire. If you over inflate your tire past the vehicle's specifications, the inner tread of your tire will wear faster than the outside edge. There is a small plaque or plate on the inside of your door, or under the hood. Always check for your vehicle's air pressure there.

After the load rating, comes the speed rating. First I'd like to say, that this in no way measures the performance of the tire. This number is only for speed and heat. It is used to measure how much speed/heat this tire can take before it is no longer certified. This doesn't mean that a tire with a lower speed rating can't go above that, just that the tire shouldn't be taken above that. This is where excess heat will start to damage the tire, tread can seperate, tires can explode. There are many things that can go wrong. With that said, lets get down to what exactly "H" means. Years ago the highest speed rating a tire could achieve was "ZR" or "Z." This was because tires of high performance nature were made with unstable compounds and couldn't be measured above a certain level. Tires that were tested had failed at certain speeds, and some made it to higher. So "Z" was rated at 150 mph and above. Now with the technological advances with rubber compounds and tread design we now have "W" and "Y." These are actually the highest a tire can achieve now, and are no longer broad range. Here is a small chart to show ratings and their top speed.

(Rating --------------- Speed in MPH)

B ----------------- 31 P ----------------- 93

C ----------------- 37 Q ----------------- 99

D ----------------- 40 R ----------------- 106

E ----------------- 43 S ----------------- 112

F ----------------- 50 T ----------------- 118

G ----------------- 56 U ----------------- 124

J ------------------ 62 H ----------------- 130

K ----------------- 68 V ------------------ 150

L ----------------- 75 W ----------------- 169

M ---------------- 81 Y ------------------ 188

N ----------------- 87 Z ------------------ Over 150

Treadwear 220 - Next is the Treadwear rating. The number 220 actually has no value. It is based on a test that is run on a test road track somewhere in the lower west of the US, and is only used for comparison. It's a means to determine the life of a tire under normal circumstances. It's to be assumed, that a tire with a 220 treadwear, will be worn down faster than a tire with 500. This number usually does give a good understand of how soft the compound of the tire is. If any of you have ever riden in a car with a "High mileage warranty," You know what I mean. Those are tires that usually have a 500 or above treadwear rating, and are extremely hard. That's how they get their long life. The softer the tire, the faster it will wear down from normal driving. There is no chart that says a 220 will last so many miles, that's all determined by climate, road conditions, and driving. I would suggest finding a good medium, on a passenger car tire 350 is a good round number, not too hard, not too soft and will probably net you a good 30,000 miles. If you want Ultra Performance, the lower, the better.

Traction A - This is pretty much self explanatory. This is the rating of traction that your tire can achieve, against other tires. This can be anywhere from D all the way to AA or AAA. A racing slick at optimum temperature would probably be AAAA. (This isn't a real rating, but using it to explain.) A street slick would be AAA. Your Ultra High performance tire would be AA, and Max Performance A. The chart goes down from there. This is what you want to look for to judge Performance of the tire. A tire with an AA is going to perform better than a tire with a B.

Temperature A - This goes along the same rating as Traction from above. This measures the amount of heat the tire can handle under driving conditions.

Max Pressure 35 PSI - This is the max tire pressure that the tire can hold before it can rupture under weight. If you were to put 40 psi of air into this tire and drive, your tire would buldge and become junk very quickly.

Sidewall 2 plies 2XXXXX Cord - This is Tire ply composition and materials used. Has very little bearing on you. More for manufacturer Standards.

Well, that is the sidewall of your tire. Always inspect the sidewall and make yourself familiar with what it says. It's always best to be well informed and know when something may happen, then not know and be put into a dangerous situation. Your tires are your stability, they can make or break you within a moments notice.

---------------

The Dreaded Runflats - First I want to start off by saying that Runflats aren't such a bad thing. When put on the right car, or right situation they can actually be quite convient, but like any other convience you must pay a price. And that price would be sacrificing handling and ride quality. The basic idea behind Runflats is simple. When they make runflats, they add many plys of rubber to the sidewall of the tire. This adds an EXTREME amount of rigidity to the tire. The basic principle is this. If the sidewall is thicker, it can hold more weight, as the air in your tire begins to expell due to a puncture, the rubber can actually withstand the weight of the car and be driven so many miles to get you to saftey, or the comfort of the nearest Tire shop. They list Runflats at being able to be driven 55 mph for 50 miles at max with zero air pressure. This is because the tire is still made of rubber and is going to start to shred at some point because of the rim. Because of all this extra rigidity in the tire, it's going to react to the road very differently than other tires that would only have 3 plys instead of 9. First, the sidewall can't flex when turning so the car is going to act very twitchy. Along with that, when going over bumps the tire isn't going to absorb any of the shock a regular passenger tire would, so you lose quite a bit of ride quality, and your car now feels like a lumber truck, instead of the gorgeous Lexus it once was, or should be. So that is basically a quick summary of Runflats.

---------------

Fix-A-Flat - Can tire sealants are another one of those convient things that were created, but like Runflats, there is a price to pay and could be large. Here's what happens when you spray those into your tire. You spray it into your tire, because of rushing air out of the puncture, the air moves the fluid into the hole and begins to seal. The instant you spray the fix-a-flat into your tire, it begins to eat away at the inside. It's almost acts like acid to the inside of your tire. Another thing you have to deal with now until you get the tire fixed is you have this liquid sloshing around in your tire, so it is no longer in balance and you get to deal with that for the rest of your trip. I don't know if any of you guys have actually seen a tire that has had Fix-A-Flat used in it once it's been pulled off the rim. It basically makes the inside of your tire into soup, and makes a huge mess. This can also lead to your tire becoming un-repairable. So if you do have to use a can of this, make sure and get the tire fixed immediately. That way you might be able to stem/patch the tire, instead of purchasing a new one.

----------------

The next thing I want to cover is approved rim widths for size tires. This is one of the most common mistakes that people make when buying tires and wheels. They want to maximize rubber contact on the road, but don't want to pay the extra money for a wider rim, so they stuff a big tire onto a small rim, and this causes a few things to happen. One, the tire is under extreme duress at all times and can tear very easily. Two, the tire can come off the bead (which holds the wheel to the rim) and you can end up damaging the wheel, and your car from the tire shredding. So it is always good to understand what tires will fit on what rims. A wheel's width is measured from the inside front lip, to the inside of the rear lip. Not the total rim's width. Here is chart that you can use as a quick reference:

50 Series tires and above (215/*50-75*/)

(mm) = (Rim width)

215 = 6" - 7 1/2"

225 = 6" - 8"

235 = 6 1/2" - 8 1/2"

245 = 6 1/2" - 8 1/2"

255 = 7" - 9"

265 = 7 1/2" - 9 1/2"

275 = 7 1/2" - 9 1/2"

285 = 8" - 10"

35-45 Series tires (215/*35-45*/)

(mm) = (Rim Width)

215 = 7" - 8 1/2"

225 = 7 1/2" - 9"

235 = 8" - 9 1/2"

245 = 8" - 9 1/2"

255 = 8 1/2" - 10"

265 = 9" - 10"

275 = 9" - 11"

285 = 9 1/2" - 11"

295 = 10" - 12"

--------------

Rotation of Tires - I am one of those people that is a firm believer in rotating your tires on a regular basis. After working with tires for so long I have come to see what can happen to tires if they aren't rotated. I have seen tires that have 50-60,000 mile tread warranties gone within a matter of 15,000 miles. The best time to rotate your tires is when you do your oil change. It takes an extra few minutes, and can save the life of your tires dramatically. In a front wheel drive car you move the front tires straight back, and criss-cross the back tires to the front. (Left rear to the Right front) RWD and AWD vehicles should be done just the opposite. Rear tires go straight foward, and criss-cross the fronts to the rear. I understand that in some vehicles this can't be done, due to having directional tires. In that case, move the front tires straight back, and the rear tires straight foward. Even doing this little bit will save you from prematurally wearing out the front tires due to more weight on them while driving and cornering.

--------------

One of the most important things that people have to deal with when purchasing wheels and tires, is what size to buy? I'm sure most of you know that your speedometer runs off your tires. They are calibrated from the factory to the factory sized tires. But, what happens when you put larger tires on your car? Does your speedometer become inaccurate? It can, but doesn't have to. When you take into account all the size factors of a tire, you can find the overall tire diameter. This is one easy way to go with different sized tires, but keep your speedometer in check. Here is a very simple forumula for you to use:

Lets take 225/55/16 to start with.

First take the section width of the tire (225) and multiple that by 0. the aspect ration, or series. (0.55) Then multiple that by 2. Divide that number by 25.4 and add your rim size. (16)

This is how it would look on paper.

225 X 0.55 X 2 = 247.5/25.4 = 9.74 + 16 = 25.74 <-- This is your overall tire diameter of a 225/55/16

So lets try to figure out what would be a good size to upgrade to without affecting our speedometer too much.

225/55/16 = 25.74

245/45/17 = 25.68

255/45/17 = 26.03

235/45/18 = 26.36

Alright, so now that we have our overall tire diameters of some tires sizes that we think will work, lets figure out just how much these will change our speedometer.

First take the new overall tire diameter, in this case we'll pick the 235/45/18's at 26.36. Then divide that by your old overall tire diameter, which would be 225/55/16 at 25.74. Next multiple that by MPH, and that will give you what your ACTUAL speed is. So it would look like this..

26.36/25.74 X 55 = 56.32 So when your speedo says 55, you're actually going about 56, which isn't such a big deal. But, your speedometer works on an exponential scale, so the further from 55 it goes, the farther off it will be. If you did the same thing for 100 mph it would be about 102 mph in actuality. Now this is with a very small margin, but think of a car going from 195/65/14 to 245/55/17

195/65/14 = 23.98

245/55/17 = 27.61

55 mph would actually be 63 mph

100 mph would actually be 115 mph

So it can add up, so be careful on what tires you choose to go with.

------------

Well guys and gals, I think that pretty much sums up the basics of purchasing wheels and tires. Just remember when buying wheels, always make sure they will fit your bolt pattern, have the right offset, and will clear any aftermarket Calipers or Rotors you might have, or be looking to buy. If anyone has any questions, go ahead and post them or send me a PM and I'll try to answer them as best I can.

Thanks for the space LOC!

-Sadistic

When you rotate tires...do you have to change anything related to low pressure warning system?--Roger

[yogapractice]

I have a 2001 GS430 and I have to buy tires again. The front tires wore on the inside of the tire? The back ones are worn uniformly. My Lexus dealer wants me to replace them with 235/45 ZR 17 for a total (mounting & balancing) of $1110.00 with an additional $145 for alignment of all 4 wheels. They offer free nitrogen inflation and tire repair for the life of the tires if the tires are repairable. YIKES! I put about 20K miles per year on my car and I love to drive and it is my intention to put another 120K miles on my car. I enjoy a high performance tire -- but is this my only choice without sacrificing the feel and the noise? Can you point me in the right direction of getting a better price?

[Lexusfreak]

What tires are you currently running on your GS & are they the stock 235 45 17 stock size?

$145 seems very high for a 4 wheel alignment to me......most places (including the Lexus dealers) offer this for $65-$99.

And are you looking to replace the tires that have a longer treadwear?

[jbgordon]

----------------

The next thing I want to cover is approved rim widths for size tires. This is one of the most common mistakes that people make when buying tires and wheels. They want to maximize rubber contact on the road, but don't want to pay the extra money for a wider rim, so they stuff a big tire onto a small rim, and this causes a few things to happen. One, the tire is under extreme duress at all times and can tear very easily. Two, the tire can come off the bead (which holds the wheel to the rim) and you can end up damaging the wheel, and your car from the tire shredding. So it is always good to understand what tires will fit on what rims. A wheel's width is measured from the inside front lip, to the inside of the rear lip. Not the total rim's width. Here is chart that you can use as a quick reference:

50 Series tires and above (215/*50-75*/)

(mm) = (Rim width)

215 = 6" - 7 1/2"

225 = 6" - 8"

235 = 6 1/2" - 8 1/2"

245 = 6 1/2" - 8 1/2"

255 = 7" - 9"

265 = 7 1/2" - 9 1/2"

275 = 7 1/2" - 9 1/2"

285 = 8" - 10"

35-45 Series tires (215/*35-45*/)

(mm) = (Rim Width)

215 = 7" - 8 1/2"

225 = 7 1/2" - 9"

235 = 8" - 9 1/2"

245 = 8" - 9 1/2"

255 = 8 1/2" - 10"

265 = 9" - 10"

275 = 9" - 11"

285 = 9 1/2" - 11"

295 = 10" - 12"

--------------

So, I have Bridgestone Blizzak LM-25 tires from a Subaru that I don't have need for anymore. They are size 215/45R17. Would I be able to use two of them on the front wheels of an IS 250 RWD, which has stock size 225/45R17? I wouldn't put them on the rears as that would change the overall diameter by too much, I'm thinking (rears are 245/45R17). Also, are there any steel wheels out there that would fit on the IS? If not and I decide to go with cheap alloys for winter, can I get the same rims for front and rear, namely 17x8" or 17x8-1/2"wheels? Would these work with the existing Blizzaks on the front as well as new Blizzaks on the rears? Thanks a lot.

[Oliver89]

My rear tire is starting to develop some cracks in the tread. I imagine it's time to replace it? Do these things have steel belts in them like car tires? I ride Continental GP 4000s and I wish the darn things weren't so expensive. Oh well