shotchkiss

Hi, I had been running 275/40 17 Victoracers on all 4 corners of my '89 C4 and am switching over to 710s in the same same. Do the 710s require a different tire pressure, something higher or something lower? I had been running 36F 30R with my Victos. Thanks.

larryfs

I run 34/33 in my victors.

Solofast

Assuming you are autocrossing the pressures for 710's are a lot lower than that.

We were running the 295/315's on a Z at 28/24 hot on concrete (1-2 lbs lower on asphalt), starting a bit lower and bleeding off pressure when they got there... The folks running the 275's on the front of Z's are running almost the same pressures, so this should give you an idea, not perfect, but it should ballpark starting place. Certainly this is a lot lower than you were running on Victors...

For a C4 (again assuming a max neg front camber C4 in A/Stock) you shouldn't be a lot higher, maybe a pound or two higher in the front and that's it...

shotchkiss

Yes, it is for autocross and the camber is maxed out in the front, somewhere around 1.75 or so per side. I'd alway kept the front pressures on the high side because i have a bad habit of overdriving and plowing the front.

So your saying for the 710s drop around 5-6 lbs from the Victos?

Barbara_S

shotchkiss - Did you autocross with the 710s yet?What pressure worked best for you? I have a similar autocross car and new 710s that I might use next weekend.

96LT1

Anything above 30 cold for the 710s is a bad idea. These tires seem to wear more evenly, getter better grip and don't delaminate or chunk when they are under 35lbs hot.

The best way to get the proper inflation for you and your driving style is get a pyrometer and take your tire temps as soon as complete a run. Prices for the simple mechanical probe (most accurate as well) are reasonanble.

Monks

For autcross on asphalt, I usually run 28/25 on my 710's

I have 3 friends with Z06's that run 28-30/ 25-27 rear

Good Luck!
Russ

TRACKMAN2

shotchkiss

Here's how it went. Ran 34.5psi front, 29psi rear as starting pressures, kept bleeding down and spraying water between runs, outside temp was in the 90s, runs were about 50 seconds. Camber is less than 2 degrees front, about 1.5 rear. Chalked the edges of the tires, rollover looked good, probe temps were as follows:

Drivers side Passenger side
115 111 115 Front 115 116 117

110 105 110 Rear 110 110 114

Does that look about right or should I come down even lower as a starting pressure?

Monks

I would start lower...5 lbs lower. I run 315's Fr/ 335 rear, -1.75
front,-1.5 rear, 1/8" total toe out front, 1/4' toe in rear.
If I raised my front to 34, it would understeeer BAD.
( FYI...I am running coil overs)

Russ

shotchkiss

I understeer a lot and end up plowing a lot also. Are you suggesting lowering by .5 psi or 5 psi per corner?
btw, have Z51 springs and bars and Koni Yellows

96LT1

Just my personal opinion but based on the temps, I'd raise the driver's side tires 1/2 psi front and rear, leave the passenger side be and go from there. I'm saying that based on the center of both tires being 4-5 degs lower than the outsides.

Those temps aren't that high (wouldn't expect much more from a 50sec run unless you were punishing them). If the temps were the same after each run that is pretty consistent.

Solofast

The temps are really low because he doesn't have much grip. No grip, no tire distortion, no distortion, no heat.....The car is likely skating on the surface with that much pressure, and yes it is going to plow like a pig with that much air in the fronts. I agree with Monks, take the pressures down 5 psi and see what it does for a couple of runs, you will likely be pleasntly suprised. If you don't like it air is free and you aren't going to damage the tires by running them that low for a couple of runs.

96LT1

Sounds reasonable. What accounts for the lower temps in the centers than?

shotchkiss...

Did you use a probe or an Infrared pyrometer to take the temps?

Monks

I am saying try 5 psi less per tire and see how it feels.

Another factor is your experience and driving style. I would
say the lower pressures ( 28fr/25rear) may be better only with
very aggresive driving that is pushing your car hard

God Luck!
Russ

Solofast

Depends on the course, how long it was before he took the temps, the probe used, and what the last couple of corners looked like, how hard he is driving...... Remember that often you are only seeing the last corner on the course with tire temps.... I would expect that the last hard corner was a left turn (higher temps on both the rt side tires)... Since the 710's have a large crown radius, some folks also tend to look at temps a bit closer to the center than they should, rather than further out at the edges. This tire is designed to work with "camber challenged" cars to some extent, and thus the rounded edge. It is made to roll over some and get a big contact patch.

Finally my suspension guru (GM vehicle dynamics expert) says that "you can't totally trust" tire temps on dot tires as much as you can on slicks. His comment was that dot race tires take much larger swings in pressures to see changes in temperatures across the tread (results from a much stiffer tread surface than typical slicks), and that can sometimes lead to one thinking he is "really close" to where he should be, when he wasn't at all.....He said that, in their experience, sometimes you have to do what works as opposed to trusting the pyrometer explicitly. It is but one tool in your racing toolbox.

If you find the tire is rolling over too much and things are all rubbery, go back up in pressure, but I don't know anybody who is running 710's anywhere near that high....

Red5

I'd like to hear Mr. Popps recomended air pressure for the 710s.

shotchkiss

My next event will be this Sat and Sun, with a little shootout going on Friday night. I'll try the lower pressures then and will let you know how they work out.

shotchkiss

28/25 worked a lot better, won my class on Sat (9 cars, 7 vettes), came in 2nd in class on Sun by .097 (7cars, 5 vettes), probably would have won my class then too, but my heat had to run on a wet track (they let cars from whatever class run in whatever heat up here, I chose badly, but what can you do).

It worked at lot better with the lower tire pressures, I just kept bleeding them down between runs. Didn't really noticing them getting really hot except on the outside edge. No matter what the tire pressure is, they don't grip when they are cold. Noticed a lot less plowing of the front end also, and managed to make it through the weekend with a spin, which is probably a first for me.

TRACKMAN2

run them even lower try 24/24 i ran mine 25 on road course but i build more heat just try it once and see what hapens mine got grippy at 175 degrees congrats on your first go round not really that scarry right...