I was talking to a Hoosier guy at Nationals and he said pressure did not affect grip but rather the spring rate of the tire and thus how the car handled. I quickly scanned the GRM issue and they did a test with Mini and A6's and there seemed to be a definate coorelation between pressure and grip. Can anyone help clarify this?

Thanks, Mike

 

I suspect he meant that pressure doesn't effect grip independently, but tire temp does, which is effected by........

 

Pressure definitely effects size of the contact patch which effects grip. I'm not countering what the Hoosier rep said because we may be talking in subtleties but the higher the pressure, the smaller the contact patch. In cases this may improve grip (if the car is overtired) or it may hurt. It also depends on a specific car's set-up.

 

He said tire prssure has no impact on contact patch because it is a steel belted radial. He said a lot of things that didn't really make sense to me.

Mike

 

Hmmm..that's interesting. My info comes from conversations with Michelin tire engineers.

For a given weight, as you change air pressure the contact patch must change. Higher psi means smaller contact patch needed to support a given weight and the opposite for lower psi.

 

I think it's best never to believe what any tire company says. They are usually just trying to stop you from getting killed or showing the limitations of their product. Talk to the fast guys and do what they do.

 

Hoosier "guy" = guy that changes tires.

I have a host of pictures that show how much the tire moves around on the rim, side to side, regardless of their "steel belts". the spring rate theory, is more applicable to the nascar cars and their tires. (e.g. 1psi = 50lbs of spring change)

mk

 

It was one of the supposed technical guys at the race. Maybe he is out of the circle track world not accustomed to road racing??

Mike

 

Be interesting to know if there is a correlation for the optimal sized contact patch for a given weight and hp.

 

to me the only strategy is to use a pyrometer. if the inside or outside are hot, play with camber. if the middle is hot play with air pressure. if the whole thing is hot, add more tire. if it's cold take away tire.

 

I am just starting to use a pyrometer but it hard to get all the info with out any help!! It sounds like I need a test-n-tune day with a little help to finetune all the pressures and other set-up items.

Thanks, Mike

 

yeah you really need to take them a full boil. that means in the pits as you come in during a hot lap. i didn't start to make progress on understanding my tires until i had a buddy in pit lane supporting me.