OK i am going to start by saying yes i searched and i read warrtalons response saying ask here so here i am .

What tire pressure should i be running on stock tires for an autox? currently i am at 40/38 and it felt ok in the parking lot not sure thats a good way to tell but it passed the chalk test.

thanks

 

I'd do the opposite, but those are in the right range.

 

the best way to tell is to play around with the pressures.

i prefer around 36 - 38 front and 32 - 34 rear, but that is just me. you might like something different. i got to those numbers by starting high and letting just a little air out of my tires each run until i was happy with them. keep in mind different days, different weather, and different surfaces may all do better with different pressures, and i am still playing around here or there.

speaking of which, i gotta hop in the shower and get my *** up the autocross now.

 

I'm a big believer in the shoe polish test. Take some white shoe polish and paint a stripe that covers a little of the tread and side wall. After a run, look to see how much is rubbed off. If there is still some shoe polish on the tread, you have to much pressure. If there is polish rubbed off the sidewall, you have too little. I have run RT-615's, Kumhos, and Hoosiers and they all settle to about 40-43 front and 38-40 rear.
I think if you are using your full tread front and rear and still have a handling problem then you need to look somewhere other than your tires for the fix.

 

I prefer more pressure in the rear to help with rotation. Perhaps those recommending more in the front have stiffer rear sway bars?

 

+1

you should run more pressure in the rear... I usually run around 36f, 38 r

 

I do have a stiffer rear sway bar. I still believe that using more pressure in the rear is just decreasing rear traction instead of looking for more front traction.
I think more pressure only becomes less traction when the tire starts to crown.
My vote is for maximizing traction front and rear and using the sway bar and toe settings to adjust the amount of over steer.

 

Warr, you still have the stock rear sway bar? Good job in the prosolo btw.

 

Yeah, stock rear bar, and thanks. What you're saying about decreasing traction in the rear applies to the rear bar, too. That's why I don't have one and why Paul Gerrard doesn't like to use one (I have his setup). It's also not so much raising pressure in the rear as lowering it in the front to increase front grip. I guess you could look at it either way, but with a rear bar, there is a significant reduction in rear grip usually. My setup focuses on stiff springs and custom valving, but there is more than one way to get it right on an Evo.

 

True.......and........True.
I finally lowered my A6's down from 45f/42r to 42f/39r and picked up about .5 second! I was just so nervous of roll over with the A6's that I wasn't using all the tire.

 

I was as low as 24/26 for the Pro, but I still couldn't get good launches on the asphalt. I went from 1.72-1.75s during practice to 1.85s during day 2 - not sure what the problem was other than spinning too much. Not sure how much the lower pressure affected my rollover either.

I have never run as high as 40 on the V710s, though...

 

I think the 710's have reinforced side walls so low pressure isn't as much an issue.

 

Run enough camber and this test becomes worthless.

I'm starting to become convinced that the only way to know is timing/datalogging and a pyrometer.

-Jon

 

Enough camber that the outside of the tread doesn't contact the pavement? What's the point of that?

 

For the OP, I have run my 9 at one event and a few fun runs with the OEM tires and I settled right in on 42F 38R, (car was bone stock) so you might be right in the ballpark. I found that as the tires got hotter they needed more pressure. IMO the car is down right frustrating to drive in autox with the OEM tires.

As for chalking/ shoe polish on tires, keep in mind that if you cook the front tires on turn in on just one corner all evidence is lost and the test means nothing. THe same can be said for pyrometers, autox is so dependant on driving technique that these tests can really send you heading in the wrong direction. Using a pyrometer on consecutive days taking averages over those days, and over the width of the tire, throwing out the numbers acquired when making driving mistakes, etc. would probrobly help considerably. That said, I dont do any of it. I personally go by feel (mostly), and run times comparing myself to other drivers in PAX and raw time.

In regards to 710 pressures, last Saturday, I went all the way up to 47F (275's) 42R (245's) and was still getting faster as the day ended. 1st in Pax, 3rd fastest raw. AS evo, 710's are mounted on 17x8 wheels.