Proper Air Pressure

[Spilchy]

Hey guys, I know this forum is about car care products, but sometimes we take a curve and speak of other car related issues.

I have Sumitomo HTR+ 225/45-17 tires - ultra high performace all season. (GREAT tire - $99 a piece)

Anyone have these, or this size?

If so, my question is, what pressure do you keep them especially in the winter and then the summer?

The pressure recommendation in my owners manual is ridiculous (29 psi). My tires chirp and go through gallons of gas at that pressure. I called the Sumitotmo and they said to use what the owner manuals says.

I currently keep them at 33 psi all the way round.

Any suggestions / recommendations?

[bretfraz]

Its best to experiment with tire pressures to find what works best for you and your car. Since were all a little different in our driving conditions and styles there is no one answer. Even the amount of load we carry makes a difference in tire pressures (don't forget its the air in your tires that holds all the weight. More air = higher load capacity).

Obviously you do not want to go over the max press rating of the tire. I suggest starting at a pressure you feel comfy with and play with them until you get a balance you like. For me it takes a month or two until I'm happy at a certain pressure.

And don't forget that air pressures drop in the winter. For every 10 degree drop in air temp, tire pressures drop 1psi. So check tire pressures more frequently in winter.

[BoxsterCharlie]

Even on the street, you can "dial in" your handling with an adjustment of tire pressure front/rear. Generally you get more grip from less pressure.

I wouldn't worry about 33 psi vs. 29, really not significant. You car should handle a little better due to the decreased "squat" in the sidewalls.

If you want to try something, try increasing the rear pressure to 36 and lower the front to 31. You should notice slightly less understeer because now your front tires have proportionally more grip than the rear. Like Bret says, try little adjustments and see how it feels. But I'd do the 31 front/36 rear combo first just to see how a fairly substantial change feels. Just be careful and do your testing on a wide road with no traffic (I once surprised myself with a 360 while "testing" some new tires which still apparently had some mold-release compound on them!).

[Veri]

I was gonna get those for my 'Bring, but ordered some Yokohama AVS ES100, 215/50/17. They've been backordered for me for about a month now, lol. Dammit.

They both beat me to it. Just play with it. I dunno how concerned you are with the wear of your tires, but you may want to be a little conservative in your experimenting... overinflated tires wear faster in the center, and underinflated ones wear the shoulders out faster. Could get pretty uneven.

[Santatime]

have Dunlop FM901's 225/45/17's keep em at 40 in winter storage, and around 34-36 summer

[James A]

Definately experiment. The optimal pressure depends of tire type, big time on the weight of the car (or weight on each tire), driving style, and location. If you are in the desert and the tires run very hot the cold settings wil be quite different than in a cooler climate. Start with the manufacture recommendations and go from there. Be very careful changing front to rear pressures to decrease or increase oversteer/understeer, it is not an intuative exercise, it has to do with slip angles and "grip".

[jonbeling]

is it possible to adjust your tire pressure to help with wheel allignment?

[jonbeling]

is it possible to adjust your tire pressure to help with wheel allignment?

[bretfraz]

Originally posted by jonbeling
is it possible to adjust your tire pressure to help with wheel allignment?

No, if you have an alignment problem its best to solve it ASAP. All you'll do is prematurely wear out tires.

Don't be surprised if your alignment probs come from worn out suspension components. Even worn out shocks will cause tires to wear prematurely.

[SVR]

I'm getting yoko avs es100's fitted to my car in a couple of days. $243 AUD each. I check my car tyres pressures every week at the service station which is 5kilometres away (i'm too lazy to get out my air compressor) and run 42psi. between 37 and 44 is what i recommend
I've got 225/50/16's. Get 725kilometres out of a 68 litre tank.

[Veri]

Originally posted by SVR
I'm getting yoko avs es100's fitted to my car in a couple of days. $243 AUD each. I check my car tyres pressures every week at the service station which is 5kilometres away (i'm too lazy to get out my air compressor) and run 42psi. between 37 and 44 is what i recommend
I've got 225/50/16's. Get 725kilometres out of a 68 litre tank.

Whoa... what are you driving? Those pressures sound awfully high.

[Shiny Lil Detlr]

Originally posted by Polaris
Whoa... what are you driving? Those pressures sound awfully high.

uh... an SVR (Subaru... I've only seen a very few of them stateside, most are abroad)

I agree with the above, just experiment and see what you like... I also agree very much with the statement about suspension components- since I've had my car (about a year and a half now) I have replaced the shocks on all four corners, the ball joints (upper and lower), u joints, and the bushings on my leaf springs because they were causing quite a few problems with traction and such. They matter as much if not more than tires and pressure.

Also remember with the front/rear thing, since one of your major problems is with traction, it will make a big difference if you're running a RWD or FWD vehicle on where you want to make your adjustments. For RWD, its better to make sure you have a couple PSI under pressure in the rear for better grip, but a few PSI over up front to help with cornering (I find it makes quicker manuvering more possible.) In mine right now I'm running 32PSI in back, with 37PSI up front (factory states 35 on all fours, tires max out at 50 for P235/75/R15's) For FWD on the other hand, you may want to reverse this, make your pressure up front be less for traction, but increase rear pressures so the rear end trails around corners faster.