JStrider

ok... i was doing my pre-travel car check(driving from texas to Cali tomorow morning)...

i looked at the sticker on the car door... it said 30psi for the front tires... and 35psi for the back...

all my tires say 35psi

do i listen to my tires... or the sticker...

oh yah... i drive a 93 ford explorer (no firestones)

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bigoldalphamale

i imagine that you would only need additional pressure in the rear if you had a payload sitting over the rear axel. but i am not very educated about trucks, so there may be some kind of dynamic that i dont know about.

to my knowledge, you cant go wrong with the same pressure in all four tires.

JStrider

yah... i will have a couple computers... a bunch of clothes and whatnot driving back... just had never noticed there was a discrepency between the sticker and the wheels and dont know if i should be worried...

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stingc

What do you mean that your tires "say" 35 psi? Is that what you measured, or what the sidewall reads? If you mean that its the number written on the sidewall, ignore it. Every car needs different pressures. What's written on the tire is usually a max pressure at some load (written there somewhere).

JStrider

thats what the sidewall says... so i guess ill keep the front a lil lower then the back like the car says

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Spyder_Venom

General rule of thumb, follow the tire manufatures suggestion - not the car manufature.

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Cynthetiq

tire people know tires... I'd follow their lead...

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shakran

follow what it says on the door unless you happen to know better. The tire manufacturers know tires, but they have no idea what car the tires are going on. The tires on your truck can also be used on vans, pickups, etc. The sticker on the door tells you what pressures delivered optimum handling performance in factory tests.

JStrider

lol... nobody can agree...

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Pragma

I agree with shakran: the pressures written on the tire itself are the recommended values from the factory, but the ones on your door are the correct values - if in doubt, read your car's manual. The car manufacturer knows what pressure tires the car is supposed to have.

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shakran

I reread my post and realized that I should clarify the "unless you know better" remark.

The door sticker on my car says 35 PSI front and rear. I actually run 35 front, 33 rear. Why the lower pressure in back? It increases the contact patch slightly, which makes it less likely that my car will spin. 35/35 would work just fine for normal driving, but I've been known to get. . .enthusiastic. . on the twisty roads

BTW, my tires say 40psi. If I ran that, i'd lose grip over the 35/33 that I do run.

DEI37

Follow the label on the door jamb. The pressure on the tires is the maximum allowable pressure for that tire. Personally, I run 34f/36r in my car, but in your case, 32f/34r should be fine. NEVER use the pressure rating on the tires. Otherwise, you'll run at 45psi in most cases, and that's just too much.

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Cycler

The reason it says more psi up front is more weight up front due to engine. Go with values written on the door. That is what I go with on my truck.

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Peryn

Go with the door jam, not the tires. If you read your tires carefully, in almost all cases they tell you a MAXIMUM tire pressure...not the reccomended. Even then, most suspension/alignment shops and tire shops have found thenumbers that work best in reality...not in a lab...and they are different than the door jam. Usually the rears stay the same, or drop a litte, and the front get more air. Sometimes upwards of 4 or more psi in front. Why? Because what weight do you have on the rear? especially on a FWD car, all your weight is on the fronts. You are gonne want some extra air in there becuase that is where the engine, tranny, and everything important is. In the meantime, all the rears have is a few passengers... if that. No reason to throw a bunch of air at that. In your case, I would feel plenty safe and comfy running 36 or so in the fronts, 33, 34, or maybe even 35 (if its loaded down) in the rears. If your not comfy with adjusting it to out of specs...go with the doorjam (unless you've significantly changed tires) reading, and know that factory specs will keep you safe.

My jeep, for example, has next to no weight on the rears. Between that and the fact that my rears are P series, while the fronts are LT (and built for higher pressure), i have 40-45 on the fronts, and 30ish in the rears and it works great. If i aired down the fronts, and aired up the rears, it'd be like dragging flats in the front and bike tires in the back, and wouldn't handle right at all.

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Spyder_Venom

Okay, lets take this into a hypathecial sistuation. I have a 98 Camaro Z-28 w/o the Z rated tire option. This means it comes with factory H rated tires, RSA's in most cases. The tire pressure that would be listed inside the door is 32PSI for all four corners. The pressure listed on the tires would be 32PSI - everything is fine and dandy. Now after I demolish this set of tires I go off and purchase a set of P-Zero's (Z-rated) tires. These say on the tire that I should run them at 45PSI, the door still reads 32PSI. Now if you run them at 45PSI the tire will maintain the proper sidewall profile and the tire will keep the correct footprint on the road. If I run the manufatures suggestions at 32PSI the tire will be like driving on a marshmellow. With 32PSI the sidewalls will buldge, the footprint will be huge and there would be a increased risk of dislodging a tire during a emergency driving manuver. It will also add stress to the sidewall increasing the breaking down of the sidewall on the tire. You will have extreme wear on the outside edges of the tire but still have an almost new tire on the middle of the tread patch. These are all things that are proven charateristics of a tire being under inflated. This is a thing that could get played out at any time and shows just how imparative it is to follow the tire manufatures suggested inflation values.



Back on topic - IN THE GM MANUAL (1995 firebird owners manual)it states that "you should ALWAYS follow the tire manufatures suggested inflation rates."



Edit- at was brought up, usually a tire lists the maxium tire pressure but in information you recived when you bought tires, it lists usually the maxium and then suggested tire pressured dependent on vehical weight. These are the numbers that you should use as a base line. These are going to be much more accurate than the factory specs. There is never a "perfect" way to figure out what tire pressures you should run. There are hundreds of factors that will change how you should setup your cars tires. Atleast with a weight table published by the tire manufature they know how the footprint will be effected by a differnce in tire pressure as well as warning off any increased tire wear due to improper inflation.

Look at this from the other direction, the car manufature doesn't take into account differnt profile or speed ratings on the tires.

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stingc

Well, you're right that different tires require different pressures, although this effect is probably small if you stay at the same size (definitely not 32 vs 45 psi). Similarly, a tire manufacturer can give a recommended pressure for a given weight, but weight is not the only factor. The factory values considered wear rates, noise, ride comfort, and performance. Several of these factors depend on the suspension setup of the car (not just weight).

It also sounds like JStriker just has one recommended number, not a table, so that would be even less accurate.

Anyway, the front-rear split is important, and you should keep it the way the door jamb says unless you specifically want to change the understeer or oversteer characteristics. Its kind of fun to play around with pressures. See what you like. It will be obvious when driving the car if the tires are over or under inflated.

shakran

No, the tire will be like driving on a tire. the Pirellis are telling you that if you run the tires any higher than 45psi, you risk blowing them. They're telling you that if your door sticker says 48psi, don't do it. Don't inflate past 45.

No matter what the tire says, you stick to the door sticker. If the tire's max pressure is lower than the door sticker, you have the wrong tire.

laconic1

This is correct. Some of these other replies are

w0n

haha, my mate pumps his rear tyres up to 45psi to make the back slip out easily

End User

Hedge your bets. Pump each tyre up with a different pressure. Problem solved.

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Spyder_Venom

The P-Zero's that I have run have a max of 60PSI and I run them at 47PSI. These are not street tires though

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shakran

they certainly aren't. Nice tires!

You're the one with the prelude aren't you? Or was it a 'teg?

Sion

J,

the one thing that just about everyone in this thread seems to be forgetting is that with tires, everything is a compromise, a trade-off. This applies to tire pressures as well as tire selection in the first place.

for example, if you want the longest lasting tires there are, you WILL be sacrificing in other areas, most noticeably wet traction.

if you want the best traction, you WILL be sacrificing longevity.

the same kinds of considerations apply when determining the best pressure at which to run a given set of tires. the final and most important factor is (I think) this: what do you want out of the tires? do you want them to last long, grip best, or give you the smoothest ride?

other factors that come into play include:
-exactly what tire do you have on the vehicle (brand, model and size)
-how you drive (aggressive vs passive)
-where you drive (climate considerations)
-how much and how often do you load the vehicle (including both the rear cargo area as well as towing)
-how much of your driving is city vs highway vs offroad
-the nature of the roads you drive most often (straight vs curvy, flat vs hilly) as well as their general conditions (smooth or pothole filled)


with the relatively small amount of info that you have provided here, I'd say your best bet is to put the fronts at 35 and the rears at 32. (this assumes that you have a tire brand/model/size on the vehicle that is appropriate to your needs).


as for the debate as to who knows better, the tire or vehicle manufacturers, I can say from my five years in the tire business that I have absolutely NO DOUBT that the tire companies know better. the vehicle manufacturers primary concern regarding tire pressures is usually comfort. they want their customers to experience a smooth comfortable ride when test driving and during the warranty period. this explains why the sticker suggests a mere 30 psi for the fronts, where the driver is. meanwhile, the combined stresses of both steering and supporting the weight of the engine, when applied to any tire running at least 2 psi low (ie at 30 instead of 32 - on a tire with a 35 max psi, 32 is considered minimum for most conditions) means that the front tires will wear out significantly sooner than the rears (that is, if you never rotate them). if you follow proper rotating maintenance, then you will shorten the lives of all 4 tires by some degree, as each tire will spend about half of its time up front and underinflated.


final note: the maximum tire pressure as stated on a given tire is also generally the optimum pressure for longest life and best traction. however, there is some leeway: you can drop the pressure by about 10% if you feel you want a smoother ride (ie from 35 to 32). but again, all the above factors should be taken into consideration to determine appropriate pressures.


also J, there was a long thread about tire pressures in this forum some months back. I know the search function is disabled, but you should look back through the back pages and find it, there was some good info there.

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rogner

Question:

I live in TX, where the temp can get up to 100+, or down to about mid 30s. My door jamb says 35psi, my tires are at about 23 or so at 60 degrees.

I havn't inflated in a while, should I put them up to 35 right now, or is there a formula one should use for inclement weather?

In addition, my tires havn't been rotated in a while (maybe 40k miles?), so I decided to do it. I bent a lug wrench attempting to remove some lug nuts. I'm no pansy, but those nuts didn't move. Does 'righty tighty, lefty loosey' apply to lug nuts?

Is there a chance they are 'rusted' on? The truck is a 1996 with 60k miles on it. No rust visible on the nuts.

Rogner

Pragma

They could have been tightened way past the specified torque values, which would explain why it's difficult, if not impossible, to get them off.

Rust, especially if you don't see any, is probably not the cause.

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leftturn109

almost all tires need 32 pounds to mantian a good bead