Ok,Im a little confused.On my inside drivers door the tire size is 225/75R15 but my 90 4Runner with SR5 package came with 31X10.50X15 which translates to a 280X75R15.What I want to know is how do I determine proper tire pressure? The 31s have a maximum 50lbs. stamped on them,but the sticker on door says 26psi front and 35psi rear but that is for a 28.3 inch tire.I guess the japanese could have swapped the door sticker info to match the SR5 package but they didnt.

 

Is you 90 an automatic transmission? If so it may have come factory with the 31's, of course that also means it has 4.88 gears in it. I'd have to say go with the psi stamped on the tires. If you notice any strange wear on the tires then adjust from there. I've always gone with what the tire says and so far no problems.

 

Unless you bought the thing brand new with the 31's, it could still be 225/75r15's from the factory. I bought mine used and it already had 31's on it, as well as some previous owner had actually put in the proper 4.56 gears! Anyhow, best bet is to go with the tires recommendation over the door plate, but I don't run mine at 50 psi. That's just the max, proper inflation does have a lil bit to do with the weight of the vehicle, too. I run 32-35 all around, and did when I had the 31's, too.

 

You should always go with the PSI recommendation on the tires. That was much of the problem with the Fords/Firestone blowouts.

Although it's probably not a good idea to fill them to the max psi.

 

Its a 5SPD,Im just at odds with myself on 50psi.According to tire "Experts" Im supposed to run them with no less than 4psi under the maximum of 50psi.So 46 each tire.

 

If you live somewhere with large fluctuations in temperature, it's probably a good idea to fill up the tires when it's cold/cool to a slightly lower psi, because the tire will heat up as you drive, and the pressure will increase with temperature. Also, as the temp warms up outside, your tires will increae psi. I believe air pressure goes up 1-3 psi for every 10 degrees of temperature rise.

I live where there can be temperature fluctuations of 50 degrees or more. When I had my 31's I would keep them at around 36-40 psi(slightly lower in winter). I've measured my pressure in the morning, and after driving in the afternoon. The most psi I've had in afternoon driving with a cold psi of around 38, was 52, and that was with a morning temp of 65 and afternoon temp of around 110. The tires were rated at 50 psi.

 

Stormin94 thats correct on the 1psi decrease for every 10 degree drop.Earlier today I added air,front was at 26 and rear at 30,now they are at 30 and 35.JonnyBoy the 2nd generations came with the 31s as an option on the SR5 package,but you got the same door sticker.Thinking about increasing to 35 and 40.Thanks to all for input.

 

like yotta4runna said the max psi stamped on the side of the tire is the MAX psi for MAX load rating of the tire everyday use you should keep it down from there unless your hauling that much stuff.
i checked my tires today at school and my tires say max 50 psi. and i put them all to around 40.

but if your owners manual or door jam says 32 psi front 36 rear or something like that then i would take that into consideration, and use my own judgment to bias the tire pressure front to rear. as they probably tell you to do this thinking you might carry some people in the back of your 4 runner or be likely to haul some stuff around hence need a little more pressure in the back tires to compensate.

 

Right Matt, it was an option. I believe the ones that had that option have the correct vin plates stating they came with 31's. I guess don't quote me, I've never seen the plate on one that I absolutely knew was a 31" packaged rig. Has anyone seen the plates on a 31" packaged rig?

Edit: I should also add that your gear ratio could help determine what it actually came with from the factory...mine was 4.10, not 4.56 from the factory.

 

I always run around 30-32psi. I wouldn't ever run anyone else's pressure. Do the chalk test and find out what pressure is right for YOUR vehicle.

 

That is damn good advice!

What I do is read the recommended max pressure on the tire (lets say 50psi) and cut that in half and add 10% of the max. So a tire rated at 50psi loaded equates to 25psi empty, add the 10% (10% of the max of 50psi is 5psi) with all the math done you come out to 30psi on that tire. It's a good place to start.

 

Jonny I think the sticker on the door is/was the same even if you got the SR5 with 31s and 4:56 gears from the factory.Thats what info I got from the net.Mines a loaded SR5 model.This is whats confusing to me,the whole why didnt they change the sticker question.

 

Also, just because x tire is OK at 30psi, doesn't mean that Y tire will be the same. Every tire is different, thus the reason I said to do the chalk test and find something that works for you. Sidewall strength, tread compound, tire size, etc... all play a roll (no pun intended) on what pressure you should run.

 

i used to drive a Chevy 3500 hd welding truck at work and i think the door jam said like 60 psi. well needless to say the truck was a bit overweight. and the tires called for 90 so we kept em at 90. haha they leaked too :| glad i don't drive that beast anymore it died 2 days before my last day before going back to school. tranny went go figure,

 

Funny this comes up, I recently wanted to check the pressure on the tires and noticed that they were a mere 32psi when the side of the tire read 50psi. Well I increased the pressure to 45psi and days later I got a major bubble on the tread making the truck unsafe to drive. Sux.

 

Toyota never changed that door sticker regardless of what size wheel/tire came on the truck. As far as inflation pressure. see below for some ideas:
- http://www.4crawler.com/Diesel/Tires...roperInflation

 

No major issues. You do have to work on finding a good pressure for even tread wear, even more so on my 33x10.50s. I usually run 25-30 most of the time and then 35-50 psi for long highway trips to even out the tread wear.

 

Thanks guys for the help.On the subject of tires,have you checked your tire manufacture date? Theres a thread on here about the dangers of out dated tires.DOT code that has 3 numbers means the tire was manufactured prior to 2000,a 4 digit code means after 2000.For example:my tires have a code of 2305,meaning 23rd week of 2005.I think that is correct code reading,if not someone can chime in.

 

Came to this topic when searching with Google for "tire-pressure".
Been busy with re-calculating tire-pressure for a while and learned myself Excell to make spreadsheets for it.
Translated some to Englisch ( so Tyre, and sorry for mis-spellings and the use of wrong words).
I use the same formula that the European Tire- and car-manufacturers use to determine the advice pressures for cars on your stikker somewhere.
American use same formula, but with other power in it, so comes to lower pressures and have to stop at 26 psi where European go down to 22 psi. So, though European sometimes comes to lower pressures, it stil is a saver calculation then the American.
American is slowly changing to the formula of the European, so in a while they will be the same.



http://cid-a526e0eee092e6dc.skydrive...0tyre-pressure
In this map spreadsheet and example with 2 pictures of it.
Always take the newest version, and from there you can navigate my complete public map of hotmail.

The pressure on the sidewall of 51 psi is the maximum pressure and not the pressure they use for calculating.
In America for P-tires they always use 35 psi as what they call Reference pressure. P-tires show though that RP as maximum pressure and state that you may go 10 psi above that. A bit strange system but if you know it you can work with it.
The diference between RP and Max P is for higher speed and camber-angle of between 2 and 4 degrees ( Tires not so|-| but so/-\ placed on the axle), for wich the RP has to be added and multiplied depending on the speedcode-letter of the Tire.

If there are questions, you can ask them here or contact me on my hotmail dot com adress with user name the same as here. ( jadatis)
Give it a title then that cant be confused with SPAM so I wont accidently delete it as such.