BlueRenesis82

Any suggestions on tire pressure? I ran 40psi all the way around with the stockers, but now that I have Kdw's on there I was thinking about 40 front and 38 rear. Any other suggestions?

willhave8

I assume you are talking hot pressures??? I don't have many track days under my belt, but with the S03's, I ran them at 36 cold which took them to 40 to 41 all around hot - after 5 laps. I then staggered the cold pressure so that each tire had the same hot pressure in them which was 40 hot. I suppose it is somewhat track dependent but at VIR this meant 35 cold in the left front and right rear, 34 cold in the front right and 36 cold in the left rear.

Having said all that, it only made me feel good as the 'noise' / inconsistency from my driving skills overshadowed any effect this did. However, my tires did not chunk with these pressures and survived the track days very well.

Not trying to steal your thread but what are the rules of thumb for tire pressures when you are seeing understeer or oversteer?

BlueRenesis82

nope, the 40 psi was cold pressure. hot pressure they were around 55 or so

mlx8

Well for a "start" on tire pressure setting suggestions:

http://www.sportcompactcarweb.com/tech/0208scc_tires/

I would welcome any other, ahhh more technical approach/suggestions for how one goes about working up a pressure scheme. For example, it seems to me that as one goes to a wider, and still wider tire, the amount of pressure required to actually support the car's weight drops? Yes, No, maybe?

Sorry, 50psi hot or cold unless it's in a bicycle tire just seems way too much pressure in a modern sports car tire. But then again, I'm willing to admit I'm no tire engineer, and the above article suggests that with Yokohama tires, the manufacturer recomends, if anything ADDING (not as I would have surmised, reducing) +1 or +2 tire size cold tire pressures by anything from 0, i.e. none, to upto +3 psi or so.

BlueRenesis82

yeah, i actually ran em with 32 front and 29 rear and they were much better than with 40 and 38, i just had way too much air in em.

rotarenvy

on a similar note; my friend and I were talking and he told me a few psi could shift 10kg or so in weight from side to side when corner balancing a car. this was on a speedway car he races. I'm not sure if tyre pressure will have the same effect on a road cars suspension but it puts another dimension to making sure you have the right tyre pressures.

alnielsen

iTrader: (4)

40 may work for autocross, but its way too much for the track. Start with recomended pressures and work up/down from there. You can also use the trick of chalking the side of the tire to check how much they are rolling over in the curves. Instead of chalk, you can use crayon, paint, liguid shoe polish etc.....
One time, while hunting for traction, I had my rears down to 24 lbs. I blistered one of those tires.

takahashi

You will be surprised rotorenvy....

Shall we do some experiment in Wakefield mate....

I ran 43psi hot in a 25 degree Cel day.

Now I have semislick I ran 36psi hot. It is way too bouncy at 44-45psi. Next time I try 38 psi hot in Wakefield and see the diff in cornering

ARRxATE

Hey guys, I only got my car a few months ago, so am running on stock everything for the time being. I've found that keeping them at 32-35 in front and 40-42 in the back makes the car a little more tail happy (oversteer) and vice versa made it understeer a little more. I stick with the extra oversteer and enjoy drifting the apex turns like a miata.

Matt RX8

I was running 34 cold last weekend at Grattan with the Stock Bridgestones. They were pretty good with the right amount of rollover, and about 41 hot after each session.

On my three track schools, I've used between 34 and 36 cold and they all worked reasonably well.

I chose 34 last weekend because I knew that the air temperature would increase by 10 or so degrees throughout the day before my first run session. I set them in the morning, so the cold tire pressure was about 35 by the time my first session started.

BlueRenesis82

Mach, cmon! The stock tires are teh suck!

Matt RX8

no worries mate, A few more track days and I'll have to replace them anyway, before they go, maybe I should enter a drift competition.

mike0615

i'm not to sure myself, but i asked a guy at the tracks the last time went, and his advise really helped me grip better. i had my front at 35 psi and the back at 38. thats cold, so after it got heated the fronts was about 42 and the back is at 45ish. it was 103 to 105 degrees that day so i don't know if that made any difference on how much the air presure increased. i heard someone tell me that if i filled my tires with nitrogen instead of regular air, the presure won't incress even when running hot. would this work for the tracks? cuz i don't think i show anyone out on the tracks using nitrogen.

Redshift

iTrader: (2)

When I run my street KDWs on the track, I find 36 cold all the way around works best for me.
Probably a reasonable place to start.

BlueRenesis82

in theory the nitrogen expands less or something like that so the tire pressure stays more constant, but unless you are racing with money on the line I don't think that you would see enough difference to make it worth it.

BlueRenesis82

Why are you running higher pressure in the rears? You would want less pressure there so they can grip better after coming out of the corners. I ran 33 29 f/r at the reccomendation of a racer...

tuj

Get a glass marker and put it all over the tread and sidewall in 3 or 4 spots on each tire. See how far it rubs off. The fronts will probably be rolling over a bit too much if you are autox'ing, so go up until they stop rolling over, then adjust the rear for preference. You can run the rears higher to make the car rotate a bit easier.

BlueRenesis82

I was going to try that, but the scrubbed area is indicative of rollover too right?

tuj

Yeah, you want the tire to show its scrubbing all the way to the shoulder, but not onto the edges or sidewall. Its its not all the way to the edge, then you can let out a bit of air.

AFAIK, most of the better autox guys (not me) are running at least 2-5 psi higher in rear than what would be indicated by the tire wear to artifically transfer loss of grip to the rear first.

BlueRenesis82

and by shoulder you mean that line all the way around the outside of the typres right?

mike0615

i told him my front tires where sliding out, i guess thats why he told me to set em up like that. maybe my aftermarket hks coilovers threw off my weight distrabution? dunno, i never got them coner balanced.

mlx8

Just finished an Audi DE this weekend at Pikes Peak International Raceway. Partial inspired by the questions raised in this thread, and my own uncertainties regarding setting tire pressures for track events after "upsizing" I decided to leave the track tires on the car, in this case the Dunlop 255/35x18's on 8.5" rims, set to @ 34psi front, and @ 32psi rear. IMO, the car ran very well. In the past I've run the same tires, as well as a second, back up set of 265/35x8's Dunlop SSR's set to @ 35/36psi cold both front & rear. With the slightly lower pressure subjectively if felt like the rear would / could be broken loose a little bit easier, but the slide was more catchable and manageable. Didn't seem like rollover was any more of an issue than with higher pressures. All in all, I think I'll stick with trying slightly lower pressures.

On to another issue however. It appears TireRack is now basically out of the Dunlop Super Sport Race, at least in the 255/35x18 and/or 265/35x18. Are the any other sources anyone knows of? or What's comparable? Just based on gearing issues, I think I'd like to switch up/over to 255/40x18's. I didn't do this earlier just because the Dunlops were such a smoking deal at @ $130 +/- a tire, but now...... looks like I'm going to have to bite the bullit on more expensive alternatives.

I'd liketo do something before the Ocotber 8/9th weekend. I can still get by with the one, slightly used set of 265/35 Dunlops, but.... Sunday we're going to get to run with the local Ferrari group (hey the Rx8 is Red, all I need is one of them yellow badge thingies), and I'd like to have some back up tires just in case the Dunlops don't hold out :-)

BlueRenesis82

where those dunlops semi r comps?

willhave8

I have never seen my TPMS light while at the track and having my tires at ~42 - 44 psi hot. Sorry, for the lazy question but isn't that outside the limits of the monitoring system?

BTW - keep this dialogue going. I am still learning about the 'why' and 'how' of setting the tire pressures from y'all. Four track days now and have generally kept my tires in the 35 to 37 psi cold range. Have played a little with them but haven't really felt any differences. (but then again, I am also learning how to drive fast and don't know what I am feeling) I just know quickly if I am on the line or not and am not driving 10/10ths very often.

BlueRenesis82

same thing for me, but I had my potenzas at 40 psi COLD, never had the light come on while at the track. I found out that that was waaaay too much air, I had way more control with like 32 29 cold f/r