Club Cobra - Tire Pressure

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I am running 17" tires and was wondering where I should start, in regards to tire-temps? I am running in a few SCCA events in the next few weeks.

Thanks

Floor it! with RaceDeck

racedeck,

I reduced tire pressure for the track from 37 psi (street) to 31 psi for street tires on my RS (YOKOHAMA 008). Track temperature was 107°F!

After the cool down lap I measured about 140°F at the tire with 42 psi pressure. although I think reducing the initial pressure with this hot track temperature is even better.
they tended to understeer during the last 3 of 10 laps. (after about 30 miles.)

this may be a good start.

dominik

Thanks for the advice!
WHen your tires raised pressure due to the heat, did you bring it back down to 31'?

Most of the events here are 1 to 2 minutes lap times ( SOLO) with a good amount of time between additional runs

Floor it! with RaceDeck

I was told that I should start my pressure at about 24# for street use? But, this brings up a good question...

How do you know what a correct or more importantly, safe tire pressure should be. Most manufactures of tires state Max pressure at 35psi. But these readings are adjusted for each individual car. What should it be for a car that weights about 2300#??????

Ren Man

Ren Man,
I'm with you. I run 24 to 26 lbs cold, and like you said this works OK for me on the street.
I find these pressures give me a nice ride, and I noticed more rear end "bite" now too. Used to run around 30 to 32 and the rears would light up more easily.
My two cents...... and now waiting for the experts to explain correct tyre pressures for us all :3DSMILE:
- Jim -

racedeck,

I let the pressure drop by 6 psi to 31 psi before the start (for 17").
Once the tire is hot I leave it where it is.

But because it was very hot these days I should have reduced the pressure even more. Never tried. Now it's cold.

all,
obviously initial (cold) tire pressures vary from car to car, tire to tire and conditions. The tire engineers that are present on every bigger event are the ones to ask.
One of Carroll Smith's Books may help here as well. Try "Tune to Win". Someone borrowed them from me, so I do not know which one answers this question.

I could just mention how much I dropped pressure from the initial (cold) value that is listed in the owner's manual. That was about 6 psi with track temp of 107 F.

For my 15" on the Cobra I run 35 psi on the street.
Track: 25 psi rear, 30 psi front.

To cunfuse you even more:
my buddy's race car with 15" wheels runs with 14 to 16 psi (cold)with sliks.

So go out there, monitor all temperatures and pressures under the same conditions and how the car felt on the track.

Bring a temperature gun and time along!

Hope that helps,

Dominik

Racedeck,

What matters is the tire pressure during the event that you are in. The reason we set cold pressure before going onto the track is to try and get the desired pressure when the tires are up to temperature. For SOLO II I would check the temps and pressures imediatly after your run and then make adjustments based on that. A new device that may be very good for SOLO events are preset valve caps. You set the pressure that you want, say 36 psi, then fill the tires to 38 psi. When you install the cap it will vent them to 36 psi, and then vent as required to maintain 36 as they heat up.

Craig,

preset valve caps: cool!

dominik