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Discussion Starter · #1 ·
I ran the last auto-x of the season by where I live. I was having issues with the sidewall rolling (stock tire size) so someone at the auto-x suggested that I increase my tire pressure. Everything felt much better after that.

I reduced some of the pressure because I didn't want to have my tires wear poorly from the extra air, What I noticed when the tires had extra air is the car seemed more responsive but the body roll on the car seemed to increase, i'm guessing from the sidewall not flexing as much.

I was wondering what is a good amount of pressure to get even wear and still have more air in the tires.
 

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Well, tirerack usually recommends 32psi all around on most passenger cars.

I usually keep mine @ 30 psi during the winter though. It helps with the ice traction.

Howie
 

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were you on the 155/80/13 tire? those have a pretty weak sidewall.

Either way the trick is to use tire-polish to see how much your tire is rolling over and optimize a low tire pressure with low tire roll.

I auto-X'd in the summer on dunlop sp r2 185/60/14's and I found myself dropping the pressure again and again as the day went on.. I usually aimed for 30 front, 28 rear (hot) Sometimes less. (I run 35 on the street)

Normally, increasing the pressure beyond an optimal pressure will result in less grip.
 

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How does the car handle doing auto-x with such narrow tires? have you though about getting wider tires like 185? I'm sure you can get 185 rims and tires off of a accent GSI. you would notice a improvement all around. Although i have never done auto-x so take it for what it's woth.
 

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Discussion Starter · #6 ·
The tires are the 175/70/13's.

I could see some slight wear on the sidewalls after my first run.

I'm looking at getting 15's or 16's but that wouldn't be until after winter.
 

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on your stock 13s running well above 40psi would be smart. I'm not going to speculate on exact pressures but I know my snow tires I run 36psi all winter and they feel like jello. The stock all seasons have stiffer sidewalls so mid to low 40s would be a good start front and rear. Shoe polish on the sidewalls will help figure out if you have enough in your tires. Without help from camber your going to be rolling over your tires pretty hard. The increased pressure will help this. You can run too much though and it will feel like your on ice. You have to feel it out and look to see where you are wearing your shoe polish off.

The rule of thumb for front wheel drive cars is there are 2 ways of getting more oversteer when playing with tire pressures.

One is to run more pressure in the rear than front. I think this gives me too much of an on the edge feel once I do start oversteering. when running stock spring rates/sway bars this is a better choice.

The second way is to run less pressure in the rear(my choice) which will provide less grip adding in a smoother oversteer transition. I've adopted a pretty wierd pressure arrangement on the blue car 36-38psi front and 26-28psi rear. If I need less oversteer i increase rear pressure a bit. Now this is for my setup with a rear sway bar on full stiff and shocks at full stiff.

My suggestion to you is just get some new wheels and tires. Your tires will make the biggest difference in handling, braking and acceleration. A 15 inch wheel with a good 195/50/15 will keep your gearing down versus a 205/50/15 but you will have less tire choices. Once you get your new shoes on then you can start playing with your tire pressure for real. Without a rear sway bar I suggest the lower front psi higher rear psi as it will make the most difference. With your stock suspension your definately going to want to run more pressure to help with response. For the street just adjust your pressures back to what works best and then when you have an autox raise then up the morning of.

Don't take any of this as set in stone because what has worked for me may not work for you. I have tried different things and this is what works best for me. It will give you some starting point but without seat time with a certain setup your going to be shooting into the dark. Try to find a big parking lot or industrial park that you can stay out of trouble in for a short time and try some things out. It is what I have done in the past if I don't have an autox to get more seat time.
 

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Also keep in mind the front is alot heavier than the rear.. somewhere in the 70-30 weight distribution range if not worse.

andy said:
A 15 inch wheel with a good 195/50/15 will keep your gearing down versus a 205/50/15 but you will have less tire choices.
:confused: are you saying a 195/50/15 keeps your gearing down and a 205/50/15 doesn't? the only difference is 10mm in the width.
 

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205/50/15 for the win....
 

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stock size wheel and tire combo(175/75/13) has a 23.3 inch diameter with 864 revolutions per mile

a 205/50/15 has a 23.1 inch diameter with 874 revs per mile

a 195/50/15 has a 22.7 inch diameter with 889 revs per mile

With as little power as our cars make going with a lower overall diameter(almost a half inch difference) will help in acceleration and the difference in width vs grip is pretty insignificant as proven with sts national competition where a lot of guys are running the 195s for better gearing while still maintaining as much grip as the 205 they were running.

hope this answers some questions
 
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