Some unusual track tire pressure recommendations (post 11 onward). Thoughts?

https://rennlist.com/forums/964-foru...rack-laps.html

Best,

Matt

 

Ay caramba.

 

Yeah, hope anyone I race follows those directions implicitly..

 

Yup, I think the crickets pretty much say it all...

 

Strange things are afoot at the Circle K.

 

I've run 75+lbs hot in race tires...but that was on the back of a fwd Showroom Stock car (stock suspension, NO upgrades or changes allowed). Car was a pushy little pig until the back tires got blown up like bowling *****. Yes...it was loose at those pressures (very loose actually), but we could make a set of fronts last an entire tank of gas if the car was loose enough. The backs would be toast in 2-3 hours, though (toast = cloth...or wires...sticking out). Also scared the crap out of anyone near us on-track (they'd opt out of pass attempts). Oh...and the guys at the tire trailer would make us let the air out before we brought them down for a change, as they were afraid the bloody stumps would explode on them.

It was a long time ago...and I was a lot more brave when I was young.

 

Those were bias ply, you could run them up to 100 PSI for the best gas mileage...

 

To be fair, the advice of putting more pressure in street tires has some merit, but requires better explanation...

The part about hard street tires gaining less pressure when hot than soft race tires do is potentially correct, even though it sounds wrong. Both are obviously subject to the same Ideal Gas Law (ie pressure change relative to temperature change), but the difference here is the definition of "hot". If the operating temperature of a soft race tire is hotter than that of a hard street tire, then it's correct so say that the race tire will gain more pressure. And seeing as how the soft race tire has far more friction (grip), I think it's pretty reasonable to say that it is going to run hotter than a street tire.

As for running street tires at higher pressure than their optimal contact patch, the most common argument I've heard in support of that is that it helps keep soft sidewalls from flexing and popping the bead. I've heard this from autocrossers, but have never seen it happen. I don't believe it to be a performance advantage, other than the fact that having a tire blow out would really slow you down. I don't really mess with that though... If I take street tires to the track, they're performance tires and have stiff sidewalls, but it's hard to want to bother with street tires anyway; race tires are infinitely more satisfying.

Depending on the car and the track, it may also be useful to run higher pressures to sacrifice contact patch for reduced rolling resistance / friction, but seeing as how we spend most of our time in the turns, that's not something I find myself wanting to try.

 

Ha ha!!!

 

Maybe they behave differently in the southern hemisphere.

 

I've heard this before, my first DE in '99 we were told to add a few psi above the factory spec for "safety" Second time was during my first visit to PDE, they were also running high tire pressures in the 40-50 psi range. It's not something I subscribe to but it is common practice at some places. I can remember running 6 psi in our old drag car, now that's low!