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Michelin PSC2 Tire Pressures

Just curious what's working for everyone with these tires on track. @Moto and I ran 38-38.5 hot as Sonoma last week. @Black Boss was running 39-40 with his and @JAJ has been running 34. Last Friday at Thunderhill it got up into the low 90's and the tires still felt good at 38 hot. These tires are pretty grippy but after two days I'm not sure I'll get more than four days out of a set. :p

B3992D2D-688F-4E44-8D70-E83CB5BC631E_zpslkmqc1qh.jpg
 
No GT350 experience yet but on Porsche they don't like more than 35psi hot before grip goes down. MPSS seem to like a few PSI more.

Peter
 
I'm running the "R" spec 305/315 PSC2's on stock GT350 rims (10.5 front, 11.0 rear). I started out last Friday at the Ridge ("TRMP") with 28 PSI all around as per Ford's recommendations. As the pressure built, they were most comfortable (for me) at around 32. By 34, the grip was fine but they were grinding in the corners so I dropped the pressures 1 PSI and tried again. Even at 33, they just didn't feel happy. So, next time out (could be next year) I'm aiming for 32 PSI hot.

I might throw the fronts onto a set of OEM 11" rears that I picked up recently (these require 350R front hubs and 35mm spacers to fit correctly). Then I'd be running 11" square rims with the 305/315 PSC2 staggered tire setup. As for alignment, I'm running the totally stock setup - mine came with 1.35 degrees negative camber and zero toe at the front and 1.25 degrees of rear camber. The car drives nicely to the track and handles fine on it. It might give up a bit of outer shoulder wear, but it's not severe, at least not yet after about 5.5 hours of track time.
 
Sean said:
Would the weight of the car come into play with this as well?
Yes. For example a Porsche GT3 has a lot less weight up front than a GT350 and can get away with a lower pressure and will have less tire wear.

Sean said:
What are you guys calling a cycle?
A cycle or heat cycle would be one session on track where the tire heats up and cools off before the next session. A typical HPDE is 20-30 minutes long and would be one cycle. After a certain number of cycles tires may get harder and lose grip. @blacksheep-1

Ok so I'll try a lower pressure at my next event in a couple of weeks and see how it goes. FYI I'm running a 305/30/19 square setup.
 
3,611
3,436
Remember guys, a pressure without a temperature reference is useless...

Assuming a tire will pick up 10 psi over cold when hot, put the tire (and you can do this w/o a temp reference) 8 psi under your target pressure, run the car 6 laps, then record the pressure asap, and bleed down to the target psi. (it's best if you have a buddy do this). That will get you close.
 
48
31
Exp. Type
HPDE
Exp. Level
Under 3 Years
Cantley
Assuming a tire will pick up 10 psi over cold when hot, put the tire (and you can do this w/o a temp reference) 8 psi under your target pressure, run the car 6 laps, then record the pressure asap, and bleed down to the target psi. (it's best if you have a buddy do this). That will get you close.
Blacksheep,
I want to make sure I understand what you said well. For example, let's say I start at 28 psi cold all around and at the end of the session the hottest tire is 38 psi and the coldest is 35 but my hot psi target is 34, I deflate all 4 tires to 34 psi right away. Next session if environmentals and driving stay the same they should all read 34 at the end of the session?
And every other day at this particular track when temp and humidity is the same I can adjust my tires to whatever cold psi I ended up with the previous time (different on all 4 tires), and at the end of the session they should all be close to that 34 psi target I set?
 
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Blacksheep,
I want to make sure I understand what you said well. For example, let's say I start at 28 psi cold all around and at the end of the session the hottest tire is 38 psi and the coldest is 35 but my hot psi target is 34, I deflate all 4 tires to 34 psi right away. Next session if environmentals and driving stay the same they should all read 34 at the end of the session?
And every other day at this particular track when temp and humidity is the same I can adjust my tires to whatever cold psi I ended up with the previous time (different on all 4 tires), and at the end of the session they should all be close to that 34 psi target I set?
Exactly
 
61
26
Exp. Type
Time Attack
Exp. Level
Under 3 Years
Bulgaria
Blacksheep,
I want to make sure I understand what you said well. For example, let's say I start at 28 psi cold all around and at the end of the session the hottest tire is 38 psi and the coldest is 35 but my hot psi target is 34, I deflate all 4 tires to 34 psi right away. Next session if environmentals and driving stay the same they should all read 34 at the end of the session?
And every other day at this particular track when temp and humidity is the same I can adjust my tires to whatever cold psi I ended up with the previous time (different on all 4 tires), and at the end of the session they should all be close to that 34 psi target I set?

But it's much better to use an infra red thermometer or Pyrometer and actually read and set target temperatures across all Inner, Middle, Outer region of each tire that way you can set a target hot temperature (176F/80C) and try to be as close to it and monitor your tires for wear. Once you set your tire temperatures correct just wait for them to cooldown the next day record tire pressures and this is your next time cold tire pressure. More to learn here:

 
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But it's much better to use an infra red thermometer or Pyrometer and actually read and set target temperatures across all Inner, Middle, Outer region of each tire that way you can set a target hot temperature (176F/80C) and try to be as close to it and monitor your tires for wear. Once you set your tire temperatures correct just wait for them to cooldown the next day record tire pressures and this is your next time cold tire pressure. More to learn here:

Throw away the IR gun, they are horribly inaccurate, I don't even use one for track temps anymore. I stick everything with the temp probe.
The other thing is don't pay a whole lot of attention tot he "across the tire tread" temps so that they are even, I've never seen them even close to being the same on a production car.
That may work OK for a prototype or formula car, but not a production or GT car.
 
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