Warning! Tire Pressure May Be Too Low!

[RX400h]

It turned out to be a bad day for my other half when she applied the brakes during rush hour traffic, on a damp, foggy morning. Yes, the RX slid into a van after the brakes were applied hard. When I got home this evening, I examined the tires and sure enough, the out side tread of each is almost gone. I then checked each tire's pressure and found them to be dead-on at 30 psi.

In my opinion, the pressure should really be 32 or maybe, 34 psi. Perhaps if a carload of people is typical, 30 psi may be okay, but be forwarned - 30 psi pressure has resulted in an accident that could've been avoided!

The bumper has a small crack in it and is very slightly tilted, but everything else is okay. I guess it's time to get new tires and pump those babies up beyond the factory-recommended 30 psi!

Dave

[katzjamr]

sorry to hear about the mishap, dave, i can tell u i have the goodyears, with excessive treadwear on the inside of the left front and rear. they have been rotated at 5k intervals and aligned twice. i am more careful with this car than anything considering the soft aluminum wheels and low sidewall. bottom line the goodyears are not a good tire with this vehicle. My real comment is many of us already run them at 32 to 34 psi for better fuel economy as i have since day one, almost 20K now. Also last month when i was at the dealer i went around the lot and found michelins on every RX, hybrid or not, save for one car, so mebbe they are phasing out the goodyears, wonder why.

[RX400h]

Katz,

Usually when a tire is wearing unevenly, it is the vehicle alignment that is at fault. This is why I can't blame the tires for this mishap. I should've been more diligent at checking the wear pattern. It looks like there is enough tread in the middle to go another 5000 miles. I think Michelins make some great tires, it's just that are so overpriced, it bothers me.

Dave

[Colo Springs RX400h]

Here's an article from Officer.com about tire pressure. It presents

a case for using maximum tire pressure. To go to the actual site,

copy the following link, paste it into your browser, and hit Go. Why

this site recommends maximum pressure and the auto manufactures

recommend something less is the question. Anyone have the answer?

http://www.officer.com/article/article.jsp...19&id=27281

SGT. DAVE STORTON

EVOC Contributor

Officer.com

How many officers check the tire pressure on their patrol car on a

regular basis? We all seem to be great at checking that the lights

and siren work, because the time to find out they don't work is not

when you get a Code 3 call. Likewise, the time to find out your tire

pressure is too low is not when you are in a pursuit and trying to

take a corner at high speed.

What is proper pressure?

The proper tire pressure for the Police Crown Victoria is 44 psi. If

you look on the sidewall of the tire, you will see that it lists 44

psi max pressure. Regardless of what vehicle you have, use the

maximum pressure listed on the sidewall. Higher pressure results in

better performance, decreased tire wear, and it lessens your chance

of hydroplaning at a given speed. This number on the sidewall

lists "the maximum amount of pressure you should ever put in the

tire under normal driving conditions." Pursuits and Code 3 responses

are not "normal driving conditions." Many agencies maintain tire

pressure at 35 psi since this is what is listed in the owner's

manual and on the door placard. The reason the owner's manual lists

35 psi is because we get the same manual as the civilian version of

the Crown Victoria. The police version, however, is fully loaded

with communications equipment, a cage, and your gear. You are not

looking for a soft and cushy ride, you want performance.

Myths about pressure

Let's put to rest some common misconceptions. The tires will not

balloon out creating a peak in the center portion of the tread when

tire pressure is above 35 psi. There is a steel belt that prevents

this from happening. Also, you are not overstressing the tire with

higher pressure, and the tire will not be forced off the rim with

higher pressure. The picture above is Bobby Ore of Bobby Ore

Motorsports driving a Ford Ranger on two wheels. The tires on the

left side have 100 psi in them, and they happen to be tires and rims

from a 1999 Crown Victoria! This is a dramatic example of how

pressure holds the tire in shape, and how much stress a tire can

handle.

Performance

If you were able to watch a tire as it travels across the ground at

high speed, you would see that it deflects to one side during

cornering. The faster you are going through a corner, the more tire

deflection you get. As the tire deflects over onto the sidewall, you

get less traction and more of a tendency to understeer or oversteer.

This could spell disaster when negotiating a corner at high speed

during a pursuit or a Code 3 run. Higher pressure keeps the tire

from deflecting onto the sidewall as much, which keeps more of the

treaded portion on the road.

A good demonstration for EVOC instructors is to have students drive

a high-speed course in a vehicle with 32 to 35 psi. Then have them

run the same course with 44 to 50 psi in the tires. The student will

experience a marked difference in performance. Having officers

experience this difference in vehicle performance is much more

effective than just telling them to check their tire pressure.

Hydroplaning

When a tire rolls across a road covered with water, the tire tread

channels water away so the rubber remains in contact with the road.

The factors that affect hydroplaning are speed, and water depth.

Conventional wisdom says that vehicles will hydroplane in as little

as 1/16th of an inch of water. Not so coincidentally, legal tread

depth is 1/16th of an inch.

Tire manufactures and the Association of Law Enforcement Emergency

Response Trainers International (ALERT) have shown that tires have

more of a tendency to hydroplane when pressure is low. This happens

because the tire footprint (the portion of the tire actually in

contact with the road) is larger. For those of you who water ski,

think of which is easier to get up on: a fat ski or a skinny ski.

More tire surface in contact with the water makes it easier to

hydroplane, just as it is easier to water ski on a fat ski. Also, a

soft tire can be pushed in more by the pressure of the water on the

center portion of the tread. This results in less rubber in contact

with the road.

Tire wear

Much better tire wear results from maintaining proper pressure.

Tires with lower pressure will wear off the outside of the tread

faster from the deflection of the tire during cornering, and the

tires will heat up more from increased road friction. This is one of

the factors that caused the failure of a certain brand of tires on

Ford Explorers some years ago. In 1999 the San Jose Police

Department realized a significant cost savings by increasing the

pressure in the training fleet to 50 psi. They soon followed up by

increasing the pressure in the patrol fleet to 44 psi. For liability

reasons, most agencies are reluctant to exceed the maximum pressure

listed on the tire for actual patrol vehicles, but they reap the

cost saving when going to 50 psi on training vehicles.

Next time you inspect your vehicle, make sure you check your tire

pressure since your ability to performance drive is significantly

affected by it. You are not driving to the store to get a loaf of

bread! You may be called upon to chase a dangerous criminal or

respond to assist another officer in trouble. You don't wonder

whether or not your gun is loaded before you hit the street; don't'

wonder whether your tire pressure is correct once the pursuit

starts. Check your tires routinely, just as you do with all other

critical equipment.

[skyfish400h]

I think the inflation issue is real, at least for the Goodyears. That's what I have and it shows the expected wear at the edges of a cronnically under inflated tire. I've had the alignment checked twice and actually set ($$$) once in the past 20K and my tires are nearly gone on the outside, while there remains usable tread on the middle of the tire.

I suppose I could drive the last few thousand miles @MAX pressure so that I don't start to show steel on the edges

[RX400h]

Some years ago, before I knew anything about tires, I used to fill my older Corvette's tires to the max pressure. Not only did this result in accelerated wear in the middle of the tires, but it also resulted in squeeling tires and poor handling. And the tires WERE steel-belted radials.

If you check with the pros at the Tire Rack, they will tell you that you should almost never inflate your tires to the max indicated pressure. I am baffled as to why any police district would support this theory. I witnessed a guy in a 96 Corvette, spin out because he had inadvertently inflated his tires to "max".

It is obvious to me that the RX400h that we have needs to have its tires inflated to a pressure that is greater than 30 psi. However, there is such a thing as going too high and I'll bet the "max" pressure would surely diminish handling in dry weather, as well as prematurely wear out the center of the tires.

[katzjamr]

Katz,

Usually when a tire is wearing unevenly, it is the vehicle alignment that is at fault. This is why I can't blame the tires for this mishap. I should've been more diligent at checking the wear pattern. It looks like there is enough tread in the middle to go another 5000 miles. I think Michelins make some great tires, it's just that are so overpriced, it bothers me.

Dave

i agree that alignment is the issue, i just feel that there is a good chance that my car was never in good alignment from day one,(it never showed any pulling or vibration other than the wear) and if i hadnt been diligent about rotation it would have shown up before 10K and become a dealer issue. If you look at every lexus forum out there you will see that almost every tire issue reported is with the goodyears not the michelins. in seattle you can buy the michelins at costco for a reasonable price, and i have bought them on sale at sears for other vehicles. speaking of price there is also a good chance the michelins will last longer. i understand the goodyears dont have a high wear rating and i will pay more attetion to that when i purchase tires. i dont mind maintaining the lexus, i didnt think i would be buying new tires before 25K on this vehicle.

[RX400h]

Performance

If you were able to watch a tire as it travels across the ground at

high speed, you would see that it deflects to one side during

cornering. The faster you are going through a corner, the more tire

deflection you get. As the tire deflects over onto the sidewall, you

get less traction and more of a tendency to understeer or oversteer.

This could spell disaster when negotiating a corner at high speed

during a pursuit or a Code 3 run. Higher pressure keeps the tire

from deflecting onto the sidewall as much, which keeps more of the

treaded portion on the road.

A good demonstration for EVOC instructors is to have students drive

a high-speed course in a vehicle with 32 to 35 psi. Then have them

run the same course with 44 to 50 psi in the tires. The student will

experience a marked difference in performance. Having officers

experience this difference in vehicle performance is much more

effective than just telling them to check their tire pressure.

Please watch this video; the driver in front pressurized his tires to 34 psi - just 4 psi over GM's recommendation.

http://www.corvettekillstories.com/photoga...ics/spinout.wmv

[skyfish400h]

Some years ago, before I knew anything about tires, I used to fill my older Corvette's tires to the max pressure. Not only did this result in accelerated wear in the middle of the tires, but it also resulted in squeeling tires and poor handling. And the tires WERE steel-belted radials.

If you check with the pros at the Tire Rack, they will tell you that you should almost never inflate your tires to the max indicated pressure. I am baffled as to why any police district would support this theory. I witnessed a guy in a 96 Corvette, spin out because he had inadvertently inflated his tires to "max".

It is obvious to me that the RX400h that we have needs to have its tires inflated to a pressure that is greater than 30 psi. However, there is such a thing as going too high and I'll bet the "max" pressure would surely diminish handling in dry weather, as well as prematurely wear out the center of the tires.

It may be the part about how these police crusers where fully loaded with gear and therefore needed more pressure in the tires (what they really needed were tires with a higher load rating, but then the recommended pressure would still not apply because the tires are different).

My dealer sets the pressure to 32psi on my Goodyears, and I still think its too low because of the uneven wear I'm seeing. I don't know what the MAX is on the tire but I'm thinking I'll run them the rest of thier life at 36 or 38 psi. I'll run some handling evaluations at various pressures (starting at MAX and working my way down) to find the most pressure it will take and still feel stable.

[jerryray]

My 400h has the michelins. So what would the max pressure be?

Is that a "Cold" pressure, because it goes up as the tire heats up?

[RX400h]

My 400h has the michelins. So what would the max pressure be?

Is that a "Cold" pressure, because it goes up as the tire heats up?

The max pressure is listed on the tire and yes, it is "cold" pressure.

[Gryphon]

It would be useful to know what the threshhold is for the low pressure sensor warning. Is this information published?

Tom

[skyfish400h]

It would be useful to know what the threshhold is for the low pressure sensor warning. Is this information published?

For those hybrids that are so equiped (my '06 400h is not), the threshold would likely be well below any of the numbers we have been discussing here.

Besides it only works if ONE tire is rolling at a different rate than the others. If they are ALL evenly underinflated, it will not set off this sensor.

[RX400h]

It would be useful to know what the threshhold is for the low pressure sensor warning. Is this information published?

For those hybrids that are so equiped (my '06 400h is not), the threshold would likely be well below any of the numbers we have been discussing here.

Besides it only works if ONE tire is rolling at a different rate than the others. If they are ALL evenly underinflated, it will not set off this sensor.

The low pressure warning in my Corvette is 24 psi, so you are correct in that this number is typically well below pressures that would result in outside tire wear.

[markusmann]

I checked the pressure on my Michelins (I just got my 2007 RX400h last weekend with 18" alloys). They are set to 32 psi from the dealer.

[RX400h]

I checked the pressure on my Michelins (I just got my 2007 RX400h last weekend with 18" alloys). They are set to 32 psi from the dealer.

This has GOT to be better than the 30 psi recommended pressure that the 06s had. Still, you might want to keep tabs on their wear patterns.

Dave

[SOMEONE ELSE'S GOT MY NAME]

I checked the pressure on my Michelins (I just got my 2007 RX400h last weekend with 18" alloys). They are set to 32 psi from the dealer.

This has GOT to be better than the 30 psi recommended pressure that the 06s had. Still, you might want to keep tabs on their wear patterns.

Dave

So hopefully no injurys. Did your 400h come with Good Years or Michelins? Our Good Year tires (even WITH continuel alignment and pressure checks over the entire 16K it's been driven) have had squirly wear from the get go, but not enough for the dealer to give us a remedy. It may be moot to check the alignment after an accident, but if it IS true ... consider NOT getting Good Years, if in fact that's what it's running.

[RX400h]

Thankfully, there were no injuries, just a bruised ego, but she'll get over it :)The tires are Goodyears and as a general rule-of-thumb, OEM tires are not the best wearing tires. I will go with Bridgestones, primarily because Goodyear's latest aftermarket tires (which have repeatedly achieved top ratings) are not yet available in the RX400h size.

[Gryphon]

Skyfish, how do you know that the RX400h uses an indirect tire pressure monitoring system? I see nothing to support this in the owner's manual and seriously doubt that Lexus would cut such corners on a $50K vehicle.

Tom

[skyfish400h]

Skyfish, how do you know that the RX400h uses an indirect tire pressure monitoring system? I see nothing to support this in the owner's manual and seriously doubt that Lexus would cut such corners on a $50K vehicle.

Tom

I read it somewhere when I was researching the car, could have been on the Lexus website. Also there was some early discussion here about why they did not include that fuction on the '06.

Besides, to measure the pressure directly would require an electrical or pnematic line going to each wheel (like on the Hummer)... we do not have that.

[skyfish400h]

30 psi is definitely too low. Did someone see that printed in the manual?

My dealer has always set the pressure to 32 psi and it has resulted in uneven wear on the sides of the tire (Goodyear) after 20K.

Just for kicks I've been driving around with 44 psi (MAX COLD) for the last couple of days, and I have the following observations:

Ride is slightly more harsh with more road noise transimtted into the cabin

Handling under normal conditions is improved w/ greater road feel in the steering wheel

Powers steering seems a bit over boosted now

Light rain afforded the oprotunity to check traction and it seems unaffected with good stops and takeoffs

Wet ground also allowed me to see how much tread is in contact with the road, the extreme edges where the execessive wear is taking place were off the pavement, but the rest of the tread was making contact.

The best part? My AVE MPG jumped 3 MPG!!!

So given these findings (better MPG, better handling, more even tire wear), I'm going to ignore the recommended pressure and run my next set of tires at 34 or 38 psi. And I think I'll run these Goodyears out the rest of there natural life at 40-44 psi.

Just as a reminder on how to properly inflate your tires:

Fill them to MAX COLD (44 psi) and drive the car to where you can let it sit (over night is best)

Let them sit until they are at ambint temperature for the season and your location

Before driving, DRAIN them to the target pressure while they are COLD

Use a good tire pressure gauge, not the ones at the gas station.

This is the most consistant method and will result in the most accurate inflation pressure.

[Gryphon]

Skyfish, how do you know that the RX400h uses an indirect tire pressure monitoring system? I see nothing to support this in the owner's manual and seriously doubt that Lexus would cut such corners on a $50K vehicle.

Tom

I read it somewhere when I was researching the car, could have been on the Lexus website. Also there was some early discussion here about why they did not include that fuction on the '06.

Besides, to measure the pressure directly would require an electrical or pnematic line going to each wheel (like on the Hummer)... we do not have that.

Skyfish, my 2007 RX400h the owner's manual states, "Your Lexus is equipped with a tire pressure warning system that uses tire pressure warning valve and TRANSMITTERS to detect low tire inflation pressure before serious problems arise. Before removing the tire from the wheel, remove the system's tire pressure warning valve and TRANSMITTERS. Be careful not to damage the tire pressure warning valve and TRANSMITTERS when removing and installing the tires." That sure sounds like a direct tire pressure monitoring system to me. Perhaps your 2006 and my 2007 are different.

Tom

[RX400h]

Besides, to measure the pressure directly would require an electrical or pnematic line going to each wheel (like on the Hummer)... we do not have that.

Corvettes have a battery-powered pressure sensor/transmitter strapped inside each wheel; there are no wires required. The original Humvees (not sure about the H2s and H3s) allowed the driver to increase and decrease tire pressure from inside the cabin, primarily to traverse sandy terrain.

Grphon,

Where is the tire pressre displayed? Is it accessed via the "mode" button?

[Gryphon]

RX400h, unfortunately the actual pressures are not displayed, only a low pressure warning light. Hence my earlier question about the threshold for the warning. I may email Lexus at some point although I expect a politically correct (eg:, evasive) response.

Tom

[SC1911]

I checked the pressure on my Michelins (I just got my 2007 RX400h last weekend with 18" alloys). They are set to 32 psi from the dealer.

I've had my RX 400h for just over a week. I checked the cold tire pressure. 37psi from the dealer.

I intend to maintain them at 37-38 psi. Its a fair balance between comfort and milage economy, keeping in mind that ride comfort is subjective.

Dealer is Metro Lexus, Brookpark, Ohio.