Michelin Pilot Sport tire pressures

[fredmeister]

Thought I would post on this forum as well as Racing Autocross Forum;

Hey, was hoping to get some info on actual cold inflation pressures for my Michelin Pilot Sport Track tires.
Took them out on my 79 930 turbo for the first time and am having hell of a time getting any front grip. The car understeers horribly, even after 5-6 laps on a real twisty course, Gingerman Raceway in Michigan.
Tire sizes are 255 rear and 225 up front, so the sizing balance is pretty normal in keeping with Porsche 911 practice of having more/wider rubber on the rear.
Measured tire pressures after 5-6 laps on the rears were 39-40psi which sounds about right, but the fronts were 33-35psi which seems low in comparison to the rear tire pressures which had lots of grip.
Can anyone supply the cold pressures they use on these tires for a 911/930?
What hot running temps should I see as well, is 40psi correct?

Thanks,
Fred

[930rsr]

I have a 1976 930 Porsche with an RSR metal conversion. I am running Lindsey Racing 9 1/2 inch rims in the front and 11 inch rims in the rear. I and running 225x45x17 in the front, and 315x35x17 in the rear. I track my car, and my starting tire pressures are 25 pounds in the front and 27 in the rear. I found that any thing over thirty pounds really depreciates the way the car handles after 15 minutes of hard driving.

[Miguel Antonett]

I have the same combination that 930rsr on my 930 but with 255x40 up front. I start - cold - 31 up front and 36 on the rear, after 5 laps they go to 36 and 40 or so; still some understeer but pretty balanced.

Michelin pilots don't come in 315x35x17

[930rsr]

Miguel, you are correct. I looked at my tires and they are 335x35x17's. I run them on Lindsey's P2's. I am enclosing of my car's setup as the car appeared at Ventura 2007 Porsche on Main street. This is my car at the Marriott hotel. I've also included a picture of the car at our local track. I have experimented with tire pressures on the PS II, and for my car starting in the mid 20's cold is proving to be the sweet spot.

-------------------------------------
Sam Moultrie
1976 930 Euro (Metal RSR conversion)
1976 BMW Group 5 Race Car
1974 BMW 2002 Turbo
1974 BMW 2002 Cabriolet
1994 Supra (Turbo)

[jay71]

930rsr- well I think the situation is hopeless. You are spending too much time sorting out tire pressures. It's time to move on. Because I'm such a nice guy I'll trade you my stock 930 for yours.

Seriously though- that is a beautiful car. Fredmeister- I hope you sort this one out.

[Miguel Antonett]

Good looking car!!!!!!!!!!

What torsion bars size front & rear are you running? Mid 20's psi's sounds a little "soft" to me, but at the ned of the day, it is a matter of preference. A softer tire will give you more swinging/bouncing ride than a stiff one which will give you a very responsive "jurky" feeling. Whatever works for you.

[930rsr]

Miguel,
I am running 31 mm rear and 23 mm front Saunders Engineering torsion bars, and 28mm rear and 23.5 mm front sway bars from the Racer's Group. I have Bilsteins at all corners with special shock valving. The car weights in at just under 2400 pounds (it's a Euro). The rear fender are a metal conversion done by Dave at TREMotorsports. Swing as you define it can be control by rear swaybar adjustment, which I have adjusted per track. I am running 1.8 degrees of negative camber in the front and 2 degrees of negative camber in the rear.

I'll end this thread now. As you said it's a matter of feel. I will say that I've had two professional drivers (Bobby Archer) and factory Porsche driver Patrick Long both drive the car. They both absolutely found it a joy to drive.

[930rsr]

Jay thanks for the compliments. It's been a twelve year labor of love.

[Miguel Antonett]

Great feedback. Your set up is a tad stiffer than mine, and same alignment. I'll try those psi next track event. Thanks!

[sand_man]

[/QUOTE]

Me, after looking at your car: "hey, honey can you please change my diapers..."

[930rsr]

Miguel, I think you're going to be very surprised. I start off in the high twenties front (29) and low thirties in the rear (31 or 32). After 15 minute my tires went away. In the mid twenties you will notice great improvement on your first lap, and it only gets better from there. It cost you nothing to try it. Let me know how that works for you. Keep in touch.

Sam

[krasuskyp]

Originally Posted by sand_man

Me, after looking at your car: "hey, honey can you please change my diapers..."

Great read on the tire pressure data guys thanks.

Sam - ohhhhh... what a niiiiiiiicely set up example. Thanks for sharing, major kudos that's *real* purty. Wow. 2400lb - HA! Oh the inhumane / impure thoughts I'm having right now, _must_leave_room_...

[fredmeister]

Originally Posted by 930rsr

Miguel, I think you're going to be very surprised. I start off in the high twenties front (29) and low thirties in the rear (31 or 32). After 15 minute my tires went away. In the mid twenties you will notice great improvement on your first lap, and it only gets better from there. It cost you nothing to try it. Let me know how that works for you. Keep in touch.

Sam

So your saying mid 20's pressure cold.
Do you know off hand what were your hot tire pressures were, this is probably more relevant because it will make more difference while on the track. You have alot of tire on that "beast" and your cold pressures will probably not change as much as the tires get warm on track.
Fred

[fredmeister]

Bump......anyone else have info?

[Dai]

I just have my wheels installed with all four Pilot Sport PS2 and they are all set at 36psi. This is set by the shop that I have my 930 worked on. I don't track my car though.

[Miguel Antonett]

IMHO, I would go to another shop...

[Dai]

Does altitude has different setting for tire pressure? How about tire and wheel size? Fitting?

Just asking.

[Dai]

Does altitude has different setting for tire pressure? How about tire and wheel size? Fitting?

Just asking.

[930rsr]

I live in Texas and the ambient (air) temp outside seems to have a greater effect on my tire pressures than any thing else. My front tires will run any where from 4 to 12 pound higher depending on the outside air temp. the rears vary far less, 2 to 5 pounds normally. The outside air temp I estimate has varied from 50 to just over 100 degree. I don't think you can establish a ratio (air temp to tire pressure) because track condition (speed) is another varible.