joey bagadonuts

No, I believe Henry was saying 44-48 HOT was the target. Which is what I believe is correct for street tires.

As for picking up >10 psi between the start and end of your session, that's an indication that your cold pressure is too low. Street tires come with softer sidewalls than a race compound, so you need to treat them differently. Lower pressures produce more sidewall flex and heat build up. To reduce any excess heat, you should start at a higher cold pressure.

Unless you are using a pyrometer, pay close attention to the increase in pressure from cold to hot. Gains should be <10 psi. Or watch your lap times (if you're at that point). The key is to keep your assessment objective. Often what "feels" best does not produce the best lap times.

Matt Lane

I would never have thunk it. In my mind you'd be running on the middle of the tread at those pressures with less contact patch. Maybe good on the straights, but hard to visualize how this would work under braking or in corners.

Has anyone else tried such high pressures (on purpose)?

My curiosity is piqued.

M

pantera43

For reference, I've run Dunlop Direzza's 225/255 17's on my 964. I start tire pressures at 32 rear and 30 psi front cold. After a 30 minute session the pressures go to 36-38 rear and 34-36 front. Tire wear has been excellent as well as grip. No side wall issues. Have used these pressures at WGI, Mid Ohio and VIR.

Dan

Matt Lane

Yup, sounds a lot like what I run, same street tires too.

M

race911

No, not on purpose. Ever. But I trashed a pair of rear (255s) Kumho V700s one afternoon at Willow Springs on the '92 C4 when I popped "set two" on without checking pressures. Because, of course, I was in a rush and had already set them within the ballpark after I mounted them. Uh huh. I was directing all kind of ill will toward South Korea about these POS tires as I struggled to do anything with the car. Came in and found the left rear shredded, even though they were shaved and started 4/32. Something like 56psi, which means I had to have started them with at least 45psi. Baffled me why I would have even had that much in them to begin with.............

Gary R.

So I guess I should run 46 PSI COLD on my R6's and then adjust them down from the 50+ PSI they will be after 20 minutes to the proven 35-36 PSI that works best?

Henry964

I´d say it again, I am just telling you guys what we do here, maybe we are wrong and you are right. I can´t really tell
We have racing drivers as coachs and teachers and tire brands who sponsor our meetings and everyone agrees on this policy of increasing cold tire pressure.
For the record I measured my tire pressure after my track run: 1 practice lap, 5 laps at full speed and 1 lap to get to the track exit and they were just 2-3 psi above cold pressure

joey bagadonuts

Whoa, whoa, Dan! Put away the flame thrower!

The subject was street tires, not Hoosier R6 race slicks. Certainly, you'd want to start with Hoosier's recommendation for hot and cold presssures and then dial it in with a pyrometer. FWIW, most of our local stock class C2 racers (3,181 lbs) target 38-40 psi.

I'd just throw out one other piece of anecdotal information to encourage those serious about maxing out their car's performance to ignore conventional wisdom and determine for yourself what really works best with your car. A few years back, Toyo introduced their R888 track tire which received a less than enthusiastic reception. Most racers simply treated them like their predecssor, the RA-1, and concluded that they were crap. But it turned out that that may have been the wrong approach:

NASA Race Forum R888 experience

Gary R.

Don't know what you have been reading but the gentleman responding is talking about track use. Don't care what the tires are, you don't start out 10PSI (cold) above what you want for hot temps. Makes 0 sense.

And for clarification -
My name isn't Dan.
R6's aren't slicks.
That wasn't a flame, it was a direct response to his opinion giving mine. Glad you aren't a moderator, I would get booted off the 964 forum... again.

Crazy Canuck

I start at 100 PSI cold on my GT3. I use truck tires with a stiff sidewall so they don't roll over on themselves when I drive flatout.

joey bagadonuts

Sorry about that, Gary.

Yes, this isn't the Race/DE Forum where you get your ***** handed to you if you misspeak or go by the user name Mark Kibort. The 964 Forum, for as long as I've been around, has always been a kinder, gentler board where people exchange opinons and perspective in a respectful and constructive manner. Rolled eyes?

But your point about bumping tire pressures above your hot target is very valid. I can see raising my cold pressures during the first, morning session while ambient temps are below the day's high. Without the extra bump, I know I'd never get near the target number on a cold, slick track.

85Gold

Finally a rational person. I'll try that tomorrow @ Barber.

Peter

J richard

I vote flaming dan off the 964 island...

But Gary is right you don't want that much pressure in a tire, race or street, you'll be past the max recommended pressures most performance tires are 44-50psi Max. On the track it's more likely an underinflated tire will fail than an overinflated one, hence the standard "add five pounds" recomended for the track. But an overinflated tire might have you sliding off the track...

I typically overinflate and the adjust down after getting heat in the tire, and usually help students read their tires and how to adjust pressures accordingly...

Gary R.

Maybe there was a language gap and i'm not understanding the gentleman properly, wouldn't be the 1st time. I know from experience my tires can go up 2Lbs of pressure just from being on the sunny side of the car in the morning. On a cold (+/- 50F) morning I will start out 4-5lb below my hot target and I usually have to bleed air out when I come in after a 20-30 minute session even then. If the day gets warmer I will be bleeding air out after the next two sessions and by afternoon will be set. If my tires are at a consistant (but low) pressure the next morning and the ambient temps will be the same I don't touch them and usually they are spot on by the second session. That's just me, my 2500lb car, and R6's. YMMV.

J richard

The 5 lbs suggested is based on average street pressures which are typically in the low to mid 30s which has you in the mid high 30s but then need to be adjusted throughout the day. Starting a little high keeps you from having to add air.

Keep in mind that this is to keep the first time DE'er out of trouble, by the time you get out of green/1 you should know how your tires behave...