added a little more tire psi how much is to much

[BigRich954]

Ok car is a little 4 door with tires that keep wearing alot on the outside but the alinment say its good.

So i was thinking of upping the tires to try and wear the center more. im running 38 psi in tires rated for 42psi.

Would upping to 42psi make a differece ?
Would it be bad to run the tires at the max psi they are rated for ? people have told it would be fine to up it to even 45 psi because im not putting a heavy load on the tires ?

 

[Eddie]

Wearing a lot on the outside & inside or just the outside? If only on the outside the the alignment IS off or you drive fast in small circles i.e corner hard allot.

 

[BigRich954]

wearing more on outside but also inside. LOL no i drive like a old old person on a sunday. now cause im alot poorer then before so im trying to save every last penny i have

 

[HTSS_TR]

If alignment is good and tire wear, either front or rear or both, on the outsides, both inside and outside, much more than middle then inflate few PSI may help. Make sure you have good tire gauge because you don't want to have any tire inflated to above max pressure on sidewall.

 

[sciphi]

If you're 1-2 PSI over max sidewall it's not going to hurt anything. If you're 10 over, then you may want to let some air out. If you hear a basketball noise when going over bumps, you've over-inflated the tires.

What's more important is being consistent. Have the fronts at the same pressure, and have rears at the same pressure.

 

[hooligan24]

arent those numbers on the tires "cold" pressure?

 

[Gene K]

I usually run a bit more pressure in the front than rear depending on weight distribution.

Ideally If these are P-Rated tires I wouldnt go over 42 psi cold max. However tires do have some extra capacity. Anyone want to guess what tire pressures hit after a 2 hour drive in 120F+ weather in Death Valley? I would slightly over inflate the tires so you can bleed them to the correct 42 psi pressure when they are coolest before you leave the house in the morning.

If these are LT rated tires 10 psi over sidewall max cold pressure is permissible (See RMA.Org).

 

[BigRich954]

I bought this gauge http://www.autozone.com/autozone/catalog...oductId=837625.

Yes id like to run a little more psi in the front to help wear the middle thiking with cold tires 45 psi ? When i say cold i mean outside air temp 90

 

[mechtech2]

What do you mean 'rated ' for 42?
I hope you are not reading the sidewall!
There are only a few words there - read them all. It will say X pressure at Y load. NOT just X pressure.
This is the #2 common mistake by civilians.
[#1 is low air pressure!]

My tire pressure advice is:
When nothing is known, 32 cold is never far off.
The door sticker should have the correct pressure - go up to 5 higher [check them cold]to get maximum gas mileage and still have good wear and handling [the ride will suffer a tad].
If larger tires than stock on on the rims, go up a few pounds more.

 

[Kestas]

I too sometimes get outside tire wear on cars that have good alignment. I probably drive more city miles than most. I simply resolve to rotate my tires more often, following the prescribed method available on the internet.

 

[SteveSRT8]

36 front, 32 rear works great on most pickups. We run 65 front and 80 rear on the service vans.

We have one vehicle in our fleet that does not require rotations.

 

[CapriRacer]

First, on every vehicle sold in the US - and I understand this is a worldwide practice as well - there is a sticker – commonly called the tire placard - that lists the original tire size and the proper pressure for that size. The placard is usually located on a doorpost or in the glove box – but sometimes it is located in the trunk or on the fuel filler door.

BTW, it doesn't matter who makes the tire or what pressure is listed on the tire's sidewall, if the tire size is the same as the placard, then the pressure listed on placard is also appropriate.

One word of caution: Some trucks use tires with the letters "LT" in front of the tire size - and some trucks use tires with the letter "P" in front of the tire size - and some trucks use tires with the letter "C" after the tire size. You should not use "P"'s in place of "LT"'s and vice versa.

For this situation, you should be sure the pressure on the sidewall equals or exceeds that pressure on the placard. If you do this the issue about the letter "C" in the sidewall will take care of itself (which is not true with "LT"'s vs "P"'s.)

If you are using a tire size that is different than what is listed on the placard, then the pressure has to be recalculated. The calculation is not difficult, but it requires tire load tables which are not allowed to be published in the Internet because of copyright laws. However, I have a copy and would be glad to do the calculation, but the starting point is the vehicle placard: Tire size and inflation pressure. I will also need to know the new tire size.

Second, on the sidewall of every tire will be information about loading and pressure. It will take one of 2 forms;

Max Load XXXX, Max Pressure YY

- OR -

Max Load XXXX at YY pressure.

Note that the first one tells you the max for each, but doesn't tell you the relationship, where the second one tells you they are related but doesn't tell you about the maximum pressure.

The reason there are 2 different forms is that the regulation is worded a bit peculiarly and it is unclear which way they want it. So be careful when you read the sidewall. Make sure you know which way it is stated.

Now to the original question:

Personally, I like a car that handles crisply. So I use 3 to 5 psi above the placard pressure. I also get better fuel economy, better wet traction, better snow traction, better tire durability, better tire wear, but I do have a degradation in ride harshness (but I am willing to put up with it.)

I don't recommend anyone use more than +5 psi (with a couple of exceptions)

 

[HTSS_TR]

Originally Posted By: CapriRacer

Personally, I like a car that handles crisply. So I use 3 to 5 psi above the placard pressure. I also get better fuel economy, better wet traction, better snow traction, better tire durability, better tire wear, but I do have a degradation in ride harshness (but I am willing to put up with it.)

I don't recommend anyone use more than +5 psi (with a couple of exceptions)


Some tires have firmer sidewalls others have softer sidewalls, for firmer sidewall tires I kept about 2-3 PSI above the placard pressure, with softer sidewall tires I like to have about 6-8 PSI above the placard pressure. For long trips of hundreds of miles or longer I like 10-12 PSI above the placard pressure, but never exceed max pressure on tire sidewall, specially if I intend to drive at 80-90+ MPH.

 

[dailydriver]

Originally Posted By: CapriRacer
I don't recommend anyone use more than +5 psi (with a couple of exceptions)


Autocrossing? Open tracking??

 

[CapriRacer]

Originally Posted By: dailydriver
Originally Posted By: CapriRacer
I don't recommend anyone use more than +5 psi (with a couple of exceptions)


Autocrossing? Open tracking??


My recommendations apply to street conditions. What folks do to make a car go around a race course faster is a whole 'nother kettle of fish!

By the same token, what is done for racing conditions usually doesn't apply to tires being used on the street.

 

[Craig in Canada]

Originally Posted By: dailydriver
Originally Posted By: CapriRacer
I don't recommend anyone use more than +5 psi (with a couple of exceptions)


Autocrossing? Open tracking??


Why would you go highly over pressure for autosports? Despite what the average driver seems to think, raising tire pressure REDUCES grip. The general rule when setting up a car is that (within certain operating limits) compliance=grip, firming up any aspect of the suspension or tires leads to less grip.

A lot of people confuse the improved turn in and sharpness of more inflated tires with grip. If you push your traction to the limit though (like at the track or autocross) you'll find that there is actually less grip.

Simplified, (ie. ignoring slip angle, hydroplaning, snow) tire traction is a static friction function which is a product of weight (including mass transfer) and surface area/contact patch. The weight on the tire is "pounds", the contact patch is "square inches" and the air pressure supporting the structure of the tire is in "pounds per square inch". Lower the psi and your contact patch area goes up. Increase the psi and it goes down. The weight is staying the same so the scenario with increased contact patch results in more grip. Of course, this only works within certain boundaries which properly support the tire (say >25psi). This is exactly why fuel economy is better with over-inflation - and no one is likely to argue that higher pressure gives better fuel economy.

In Formula 1, for instance, the tires are relatively large and the car weight is very small. Thus they run pressures of something like 15psi.

So, a lot of track guys will put chalk on their sidewalls and start at the higher end of the pressure spectrum. They'll do hot practice laps, check the chalk marks and reduce pressure until they are using all of the available tread surface in their typical turns and stop there.

 

[CapriRacer]

Originally Posted By: Craig in Canada
.........Why would you go highly over pressure for autosports?........


A lot of reasons:

1) Using higher pressures reduces the heat generation, keeping the rubber compound in the proper operating temperature.

2) Using higher pressures increases the spring rate - and if you're racing in a class where you are not allowed to change springs, this increase in spring rate reduces the roll angle, and that does wonders for the overall handling.

3) Like you said, the quick turn in is sometimes worth the sacrifice in lose of grip.

Originally Posted By: Craig in Canada
.........In Formula 1, for instance, the tires are relatively large and the car weight is very small. Thus they run pressures of something like 15psi........


Racing tires are a whole different kettle of fish. They are designed from the git-go for this purpose. But when you take street tires and trying to race with them - well, sometimes you have to do unconventional stuff.

Originally Posted By: Craig in Canada
.........So, a lot of track guys will put chalk on their sidewalls and start at the higher end of the pressure spectrum. They'll do hot practice laps, check the chalk marks and reduce pressure until they are using all of the available tread surface in their typical turns and stop there......


My experience has been just the opposite. They start too low and keep raising the pressure until they get rid of all the tread roll. But the biggest problem is that it is difficult to dial in enough camber to keep the tread in contact with the ground. So you just do what you can - and sometimes that means pretty high inflation pressures.

 

[Geonerd]

Keep in mind that the owner's manual / doorjamb pressures are often a compromise. The marketing monkeys like soft tires because they soften the ride and make the customer happy; the engineers want more pressure, for improved handling and decreased tire wear.

FWIW, my old Accord officially wants 32psi. This is hopeless, causing notable tread-edge wear. I need 37~38 for the tires to wear evenly. I'm running 40psi. Doing so greatly improves handling, allows for a bit of leakage, improves hydroplaning resistance, and may squeeze a few tenths of a MPG. However, much beyond 40PSI, the ride starts to get harsh.

IMO, increasing doorjamb pressure by ~15% won't hurt a thing, and is well worth trying.