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Hoosiers and tire pressure


mikew968

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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?

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Sounds like he is sayiing that the maximum "grip" potential of the tire itself won't change with pressure. Even though the way the car handles definately will. Pressure certainly has a role in overall "grip". The fact that the contact patch will change with pressure variations answers that.

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Interesting question, Mike.

 

Hoosier's web site says cars in our weight range (2600-3000 lbs) should be in the 37-41+ pressure range. In my conversations with Hoosier guys, they have always said 35-36 without asking about the weight of the car. The web site, again, notes that "Higher pressures will improve the performance capability but will require a more sensitive feel to take advantage of the increase."

 

But, they also say...

 

INDEPENDENT REAR SUSPENSION: With IRS and proper geometry up front, tire pressures can be reduced from the recommendations listed above. When there is adequate camber gain and good roll control, the Hoosier radial tire will perform very well at the reduced air pressure. This results in a bigger "sweet spot" and easier control at the limit.

 

When tuning at reduced pressures use the following formula to determine the minimum safe pressure: Divide the total vehicle weight, including fuel and driver, by 100 to arrive at the minimum safe pressure. Example: Your car weighs 2750 lbs. as raced. The minimum safe (cold) pressure is 27.5 psi.

 

So...I dunno.

 

I know I have been shooting for 35lbs hot, which has worked pretty well. Reading this, what I think I'm finding is that may be working well because it's forgiving but that it may very well not be the absolute fastest option.

 

This has me thinking I need to start doing some experimenting with slightly higher pressures and what you heard along with the comments noted above actually combine to make more sense than some of what I've heard in the past from the Hoosier guys.

 

In playing around with tire temperatures, I have noticed several times that mine aren't really where they need to be. Typically, they have looked to me like I needed to raise the pressure to get more heat into the center of the tire(s). When I've asked the Hoosier guys about this in the past, they have bascially said, "don't worry about that...just get the pressures in the 35-36 range," but that has never really sat right with me. I think maybe they were giving the safe/easy/not-wrong answer.

 

Sounds like we've got something to play with at Putnam!

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Well it is always personal preference, but I can tell you that 35-36 is too low.......38-40 is perfect.

 

And what is alluded to by Hoosier in the above reference from the Hoosier site is....

 

The higher the pressure the more sensitive the car will be and the faster you will be.......if you can drive the car comfortably at higher pressures you will be faster. Remember though, "comfortably" in this sense is a relative term. Not a Sunday drive comfortably, but an all out on the edge, but I'm still having fun and am not ready to change my undies (but almost) kind of comfortably.....

 

Does that help ???

 

 

Phil

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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?

 

Note the scale of the grip vs. pressure graph in the GRM article. Percentage wise there was not a big change in grip at the various pressures used.

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