Tire Pressure

[Straub]

What is your tire pressure and what tires are you using?

Michelin P235/55R18 99V

I drove my 400h home from the dealership on friday and checked the pressure, my front tires were 37 & 37.5 psi and my back tires were both at 38. I filled them all up to 38psi. I noticed the max tire pressure on the wall of the tire is 44 and the recommended tire pressure inside the drivers door is 30. Just curious what tires and psi other people are using and how they think it is affecting their mileage. I drove 300 highway miles home and was getting around 22mpg @ 75mph.

[RX400h]

Dealerships are notorious for forgetting to deflate the tires to the door sticker-specified pressure. For obtaining the longest life possible out of your tires, use that pressure as a starting point. You may have to raise or lower it, depending upon ambient temperature, but probably not more than +/- 3 psi from that printed on the door sticker.

Dave

[katzjamr]

the tires are shipped at 40 psi on the 400h to avoid flat spots, and as 'rx400h' noted many dealers, mine included, never lowered the pressure during what passes for dealer prep. after reading about the high tire pressure issue in this forum last year, i arrived at the dealership with a digital tire gauge and to my salesmans chagrin lowered the pressure to 32 before driving away. the dealers do themselves a disservice too because when i test drove the 400h that had arrived for me it rode harder and handled differently than the demo vehicle because of the high tire pressure. lastly you do not mention if you have the goodyear or the michelins each has a different recommended pressure. IMHO 38 is too high for a comfortable ride and will cause the crown of the tire to wear sooner. i prefer 34 in the goodyear eagles, hope you have the michelins they are a better tire.

[Straub]

Thanks for the replies!

I do have a set of michelins. 30psi sounds so low. I think I will try out 34psi. If i risk premature and uneven wearing of the tire I would just assume preserve the tire and have a more comfortable ride than save any mpg.

[Straub]

Thanks for the replies!

I do have a set of michelins. 30psi sounds so low. I think I will try out 34psi. If i risk premature and uneven wearing of the tire I would just assume preserve the tire and have a more comfortable ride than save any mpg.

I just checked my tires again and they are now at 36psi. The temperature is dropping :cries: I didnt think temperature would have such a drastic effect on the tires psi.

[retired00]

I just checked my tires again and they are now at 36psi. The temperature is dropping :cries: I didnt think temperature would have such a drastic effect on the tires psi.

You can figure about 1 lb air pressure for every 10 degree F change, given a cold tire and sitting overnight.

[lexus411]

switch to Nitrogen. The tire will hold the pressure much longer and is better for the overall tire life.

[Straub]

switch to Nitrogen. The tire will hold the pressure much longer and is better for the overall tire life.

Uhh, where would one be able to fill up their tires with Nitrogen?

[skyfish400h]

I just checked my tires again and they are now at 36psi. The temperature is dropping :cries: I didnt think temperature would have such a drastic effect on the tires psi.

You can figure about 1 lb air pressure for every 10 degree F change, given a cold tire and sitting overnight.

It should be noted that the recommended tire pressures are for COLD tires. That means they have been sitting overnight, but it assumes standard day conditions (i.e. sea level and 75 deg F).

If you are going to adjust your tire pressure, it is best to fill them up at local air source (unless you have your own) the night before and then "drain" them to the proper setting the next morning.

If your morning is 65F or 55F then you can subtract a pound or two from your target setting based on the above formula.

NEVER SET THE TIRE PRESSURE AT THE FILLING STATION!

They will be severly underinflated.

[Straub]

:P

I just checked my tires again and they are now at 36psi. The temperature is dropping :cries: I didnt think temperature would have such a drastic effect on the tires psi.

You can figure about 1 lb air pressure for every 10 degree F change, given a cold tire and sitting overnight.

It should be noted that the recommended tire pressures are for COLD tires. That means they have been sitting overnight, but it assumes standard day conditions (i.e. sea level and 75 deg F).

If you are going to adjust your tire pressure, it is best to fill them up at local air source (unless you have your own) the night before and then "drain" them to the proper setting the next morning.

If your morning is 65F or 55F then you can subtract a pound or two from your target setting based on the above formula.

NEVER SET THE TIRE PRESSURE AT THE FILLING STATION!

They will be severly underinflated.

I have a digital pressure guage and just use the air at my local filling station to fill them up.

I am pretty sure COLD means something completely different up here than most other places :P

[Husker4theSpurs]

Straub,

How much do you think your mpg suffers when it is colder out? Maybe you haven't had your car long enough to know :)

[Straub]

Straub,

How much do you think your mpg suffers when it is colder out? Maybe you haven't had your car long enough to know :)

Ya, I haven't had it long enough to tell. Its been below 50 since I picked it up and it will not get above 50 degrees for another 6 months :cries:

I am not getting very good mileage averaging 22mpg on the highway (going 75) on 200 mile trips. I am averaging about the same in the city with the short trips. Once it is warmed up I can reset the mpg and average around 35 in the city. When I take it in for its 5k checkup I will ask them to run that ICS or whatever it is to recalibrate the system.

[katzjamr]

in seattle when it gets cooler in fall and of course winter we see a 3 to 5 mpg penalty for cold weather. for low emissions the engine has to keep the cat converter heated to 800 F or so, heating the cabin, and a cooler battery pack all add up to mpg penalties. it is no accident that when toyota demos these cars to the press they pick a warm climate like hawaii. straub since you have only had the car in cooler weather, i promise a spring and summer benefit is comming your way.

[SOMEONE ELSE'S GOT MY NAME]

switch to Nitrogen. The tire will hold the pressure much longer and is better for the overall tire life.

After tons of reading, it seems like the whole nitrogen thing, at best, is a wash. Heck, after you shell out $15 or $20 bucks for it, then quantify extra mileage ... poof. I mean what with regular ol' air containing 78% nitrogen, ultimately all one would be doing is paying for the additional 22% ~ seamingly.

[Statman]

After tons of reading, it seems like the whole nitrogen thing, at best, is a wash. Heck, after you shell out $15 or $20 bucks for it, then quantify extra mileage ... poof. I mean what with regular ol' air containing 78% nitrogen, ultimately all one would be doing is paying for the additional 22% ~ seamingly.

The main purpose for using nitrogen is that it has less moisture in it. The other reasons are probably unperceptable to us regular folks (e.g., size of nitrogen molecules, etc.).

[Gryphon]

I am undecided about the benefits if pure nitrogen versus the inconvenience of adding more if/when the pressure drops. Costco does it for free in Arizona so I gave it a try. I may have a later report.

Tom