Rob Heath

Started at cold 36R/29F on a set of Bridgestones. As the hot day hot track and tires were quickly increasing pressure. So my question is are you trying to maintain the 36R/29F at hot pressure measurement by releasing pressure?

Thanks!
Rob

KILRWAIL

I use 30F, 34R cold and reset it to those values just before each stint. The tires gain about 3-4 psi after a couple of laps. The day after the event, I have to add about 3-4 psi to restore those cold values.

Minoclan

I go by the tire manufacturers recommendation for hot pressures and adjust ASAP as I get off the track.

ivangene

when is your DE, mine is TODAY

Rob Heath

Hey Thanks everyone for their thoughts on tire pressure.

My DE was last Sunday and it was great. It was my 4th DE and it was a blast! Moved up out of the novice run group. My next thing to work on is better braking

It was really hot and my tires went from the factory setting to almost 6 pounds more on the first run. A little bit more let out end of each session (checked immediately) ...ended up releasing almost 10 pounds out both F/R by the end of the day. Not sure it was enough.

Have looked at the Bridgestone tire site and don't see hot pressure recommendations.

Thanks!

Tango635

As you know, pressure will increase with temperature, so it would be nice if they provided a chart.

I haven't done any DE's yet, but I wonder at what point you should start considering using nitrogen, if at all??

race911

You're not going to get a chart from a tire manufacturer for hot pressure characteristics on street tires. It's hard enough with slicks and R compounds. Basically you just figure it out. In the old, old days, BFG recommended mid-high 30s (hot) for the original RA1. (This is NOT in any way, shape or form the tire that is out now.) But we, competitive edge seekers that we were, ran them down as low a 22psi hot, groove of doom be damned.

If you want to run N2, feel free. What's the composition of the air you just breathed? Knocking out that last ~20% of non-N2 isn't anything I've ever really worried about. Now, making sure you've got reasonably dry air to begin with, post-mounting, is a plus.

I've not run more than probably 5 laps on street tires in the past 15 years, so I can't speak to what will/won't work to the question at hand. What I do recommend to my beginner students is that you start with the recommended cold pressure, and slightly fiddle with things as you progress. If I had to strap into a stock torsion bar 911 with high-end street tires right now, I'd take a WILD stab that I'd be looking for 36-38psi at the end of the session, front and rear. Then I'd reflect on grip level and adjust the front pressure.

Bob Rouleau

Rob,

Your street tires will perform best at around 36 lbs in Front and 38 lbs in the rear measured HOT. Depending on how hard you drive, starting cold pressures should be about 6 lbs less. If your tires get over 40 lbs HOT the car will have a tendency to slide. Check pressures as soon as you hit the pits and expect to have to bleed off some air as the day progresses and gets hotter.

Once your track day is done, go back to factory pressure to drive home.

MUSSBERGER

And before long you'll be adjusting side to side based on the particulars of the track.

rusnak

Use chalk on the shoulder, and adjust accordingly.


http://books.google.com/books?id=nPp...nge%22&f=false

Ed Hughes

This varies widely from tire to tire, although not as much on streets. Find someone running the same tires and trade notes.

When I ran MPSC's, they didn't like going over 36psi....my Yoko A048R's like to stay lower than that-closer to 32psi. Both are R compounds, but different behaviour. The MPSC's also took an extra lap to heat up in decent weather, 2 laps if below 60F ambient.

As noted, you're concerned with temps immediately after a session. Don't worry about checking them before a session as the day progresses, you'll probably be bleeding off as the day goes by.

Bob Rouleau

I agree about R compound MPSC tires, on my car 35 max in back and 32 in front measured hot. The OP refers to street tires however.

Rob Heath

Thanks everyone next time out will try to shoot for 36F/38R hot and see how that goes. One afternoon run I was starting to slide around / squeeling and was at 42R when I checked. In retro may should have come in mid -run measured and released some pressure.

Rusnak thanks for the link to the Porsche 911 Performance Handbook / chalk reference. Don't have that book, so much to learn.