I need an EXPLANATION !!!!

[WBlackburn]

On every vehicle there is that little tag on the drivers side door that tells you the recommended tire inflation pressure for the vehicle. (OK got it)



Now you buy a pair of tires,(stock tire size that came on the vehicle) and on the tires is a recommended max inflation pressure. (OK got it)



Now my question is WHY is there so much difference. I relize that if your hauling heavy you should pump up your tires to the max tire pressure recommended. . but... the difference on the tag on the vehicle and the max pressure on the tire will be from 40 - 60 lb's different. It just dosen't see to me that a tire should be run at such LOW pressure when empty.



Example... On my tag on the vehicles it recommends 32 psi... on the New tires I bought it recommends 60 psi. ??????? This is on a vehicle that hauls NO LOAD!!!!!



I'm sure there is a simple explanation from some of you ole tire guru's out there so educate this ole man.

 

[Redmega06]

If you want my opinion I would say that they are all just ball park numbers but your real air pressure should be based on wear. I understand that if you just put a heavy load on that you are not going to drive far enough to adjust air pressures but for everyday driving you should be able to adjust a couple pounds each way to get perfect wear across the entire contact patch

 

[Forrest Nearing]

the tires list the max pressure... the door tag lists the suggested pressure... two totally different numbers.



what I do when I put new tires on is pump them all up to max and get out on the road for a while to get some heat in them. use a temp gun or your hand to feel across the tread. you want nice even heat across the tread.



if you're warmer in the center than the edges, drop the pressure 5lbs and re-test. it'll take you a bit to figure out your best pressures, and they'll differ from front to rear, especially w/ nothing in the bed.

 

[rbattelle]

Forrest has an interesting method, although there's no way my "heat sensing" is sensitive enough to detect subtle variations in temperature across the tire.

I've always figured that the max pressure published by the tire maker is a never-exceed bursting pressure sort of thing.

Ryan

 

[DodgeWarlock]

Another method is to rub chalk or tire crayon on the tread and drive a short distance. If the wear is only in the center they are overinflated. If the wear is on the edges only they are underinflated. If it's only on one edge you have an alignment problem. It's cheesy, but it works.



As for the pressures, the sidewall is a max cold for the tire. It can and will be slightly higher as the tire heats. The door sticker is a factory reccommended pressure with the stock size and load range. Be aware though that part of the Firestone/Explorer debacle was because Ford reccommended a borderline pressure for improved ride quality that when unchecked quickly led to tire failure.



Also be carefull when buying new tires. I recently had a relative buy tires from a supposedly reputable Good/year dealer who put c-range tires on his 1-ton suburban after he asked for commercial grade tires. Another local tire shop only put 32 lbs in a new set of tires for me recently for our diesel and said their policy was not to inflate any tire to anything other than that unless specifically instructed by the customer.

 

[Pawpaw]

Back in 1976 I bought my first brand-new car... a Pinto station wagon. NO LAUGHING!



The door sticker said to run 24 in the front and 26 in the rear. As a know-it-all 23-year-old, I "knew" that you always inflate tires to the 32 PSI that it states on the sidewall.



Imagine my surprise when the tires were bald at less than 20,000 miles.



Bob

 

[Missouri Mule]

I've read where the recommended (required) tire pressure on the lable is the pressure the front end will take (front end components where out faster or break).

On my Mule I do run the front 10 lbs over factory recommended pressure (70 instead 60).

On my former 1 ton ford van if I aired up over what was recommended it did not handle or ride right.

 

[Steve St.Laurent]

Look at one of your tires again. You'll see it will say something along the line of Max 65 psi @ 3,305 lbs (this is what my 285/75R16 D range BFG AT/KO's are rated at). So if your going to put 3,305 lbs on that single tire (6,610 on that axle - two tires) then you should have 65 psi in them. If you have less load on the tire than that then you should have less air in them. My truck for example when unloaded weighs 4,400 lbs on the front axle and 3,000 on the back. I put my front tires at 55 and my backs at 45. I came to those numbers using the chalk method described above since my tires are neither the stock size or rating. The sticker on your vehicle is based on a stock size and stock tire rating (E for our trucks).

Given that my truck is rated for a GAWR of 4,850 lbs in the front and 6,500 in the rear you can see that as long as I'm inside those ratings I'll never fully load these tires and therefore never need the max psi in them.

 

[betterthanstock]

A tire runs best when it deforms a certain amount. So, you want the tire contact patch (flat spot) to be equal, whether loaded or unloaded. That's why the variation in pressure.



To clarify, at half the load, you need half the pressure.

 

[brods]

Here is a link that explains it pretty well and gives some formulas too.



Technical Information: Tires

 

[WBlackburn]

Lot of good information. Thanks gentlemen. beods that web site if excellent.