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Discussion Starter #1
I know GMC recommends 30 psi for the tires on this fine car, but it seems too much to me. Is anyone running less than 30 psi? I was going to drop to 28 and try that, but figured maybe someone her has traveled this road already. How 'bout it bros?:-? Bill
 

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In previous posts I've seen guys running at 34 PSI front and back. Frankly, I'm not certain what's best so I go with what's recommened. Seems to work fine.
 

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70boss302


Lots of folks running diff. Pressure for diff. type Racing Events. Mine I'm running @ recommend Pres.............
 

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Discussion Starter #4
FYI, I just did some prehistoric type testing. I left a small burn out on pavement and noticed a thinner tire mark than the tire width. I dropped down to 28 psi and tested again, much better but not perfect..................finally I settled on 25 rear and 28 front. The car does seem to grab a bit better and is still very tight in the turns. More testing tommorrow!;) What are you race guys running? Bill
 

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A word of caution if you run lower tire pressures. Check the pressure often. The tires are made to lose 1/2 to 1 lb per month. A major tire mfr sent engineers around the country to check tire pressures on the Ford Explorer. They were randomly tested in parking lots at shopping malls. Avg tire pressure was 16 lbs. As I recall, they left the factory at 26 lbs so they would have a soft and comfortable ride.
 

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Pressures...

I run 31 front, 30 rear for street. Before my Hoosiers and Goodyear slicks came in I autocrossed the F1's.

I originally started at 30 front and 29 rear (cold) . for auto cross. Tire temps were even across the tread.
Then dropped to 29 front and 27 rear to get more traction. Lost only 1 degree in the center tread.Times were 1 -2 seconds faster.
Dropped to 27 front and 25 rear (cold).
Felt tires "rolling" just a bit on maximum turns. Tire temps dropped 5 degees in front center, 3 degrees in rear center. I was out of the gate faster with better hookup but was slower on course, times inceased.

Hot tire pressures never got above 35psi, but I am running 100% Nitrogen in them. Hottest tire temps were at 29 psi cold (89 deg.), 118/117/118 degrees (hot) in front.

For Solo I, I ran tires at 28 front and 25 rear with minus 1 degree in both front and rear center tread (hot). Others I know ran as low as 20 front, 19 rear on the track but I did not go that low. They were not any faster.





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What some of us in the offroad world will take a piece of chalk and make a line across the entire width of the tire. Drive for about 100 yards and see how much line has been made. Then you can adjust your pressure to get the correct contact patch. This is a big problem when you go to larger tires on 4x4's and such as less pressure is needed. Hope that helps. Good luck :) .
 

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another technique.....

.... for autocross is to chalk the sidewalls radially (like spokes) in at least three areas on a tire. Make a run or 2 and check how much chalk is removed from where the contact patch meets the side wall.

Next decrease the tire pressure in 1 psi increaments and repeat the runs and check again, trying to be as consistant as possible; until the chalk starts to be removed from the side wall. You have now theoretically reached the point of maximum traction and tire stability. Reduce the pressure further and the tires will "roll" on the sidewall under hard cornering (a very bad thing) and the car will start to twitch and become "squirrely" in the corners. This will cause a sane driver to feather or modulate the throttle and actually slow down. An insane drive will spin. Fortunetly in the Z06 the Active Handling will become more active and you can actually feel the brakes modulating. At this point some add 1 psi for safety.

On the F1's I have noticed that you can tell when this point is reached when the rolled edge of the tread (at the point where the tread meets the sidewall) starts to become ruff or scuffed. It will almost have a "snake skin" feel and appearance.

Be careful of cold F1s the tend to skate just like slicks do when cold. They are much better, and have better manners when warm.
Similar to my wife, I think!
 

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Another thing that may be of interest is : for every 10 degree change in ambient air tempeture, there is an app 1# change in pressure.

So if you do not take the tire pressure right before you run the tire, factor that in, from the time and temperature of your last pressure check.
 

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I've been runing at 30#, and have measured the tread depth in the past and the tires are wearing nice and even. Of course, I'm not racing.

I did, however, let the pressures get down to about 28# one day, I noticed the car hooked up a bit better off the line. At the drag strip this saturday, I'll probably run 27 or 28 in back.
 

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I have found that going below 28psi rear at the strip doesn't help at all. The width of these rear tires need that much pressure to create a flat patch to help you on your 1-2 shift and 2-3. At take off a lower pressure does help a little but if you speed shift to second you'll probally lose time because of traction loss due to the smaller contact patch.IMHO:)
 

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Discussion Starter #12
Thanks for sharing info here brothers. So far I have settled on 26 rear and 28 front and like the feel and response. Tight but still getting good feedback from the wheel and the rear seems to hook up considerably better than with 30 psi. I will watch tread wear and "keep an eye on it". Maybe for casual driving 30 lbs is good enough, but to stay young, well you see what I am running! Hey, drive it like you stole it;) . Bill
 

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The best et's I have goten were with 28lb in the rears. On the street I like 30-30 or 32-30. Ric
 
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