| Author |
Message |
Dennis (Bighead)
Member
Username: Bighead
Post Number: 265
Registered: 2-2003
| | Posted on Friday, October 17, 2003 - 10:34 pm: | |
Brian's got great advice.
One general rule of thumb - for modern street rubber (NOT R-compounds, and NOT slicks), the target pressure should be 40 lbs. HOT all around. Depending on the track, car, speed and weather, you'll probably start between 31-35 psi. Re-measure immediately when you finish your session. Good place to start; you can adjust from there.
vty,
--Dennis
|
Crawford White (Crawford)
Junior Member
Username: Crawford
Post Number: 200
Registered: 3-2003
| | Posted on Friday, October 17, 2003 - 3:07 pm: | |
I'd say that about covers it all - thanks Kennedy! |
Brian Kennedy (Kennedy)
Member
Username: Kennedy
Post Number: 501
Registered: 3-2002
| | Posted on Friday, October 17, 2003 - 12:33 pm: | |
The best advice depends upon the audience. Let me try to be a bit more precise.
Generally speaking, lowering pressure increases traction of the tire, but this is not always the case. However, you never want to lower the pressure enough that the sidewall starts to roll over. So, people often will put a bit of shoepolish on the edge of the sidewall so they can see if the tire rolls over at a particular pressure on a particular course. They then lower pressure as low as they can go without that shoe polish getting rubbed off.
Why do some people recommend to newbies that they add a few pounds? Because newbies are typically on all-season radials that weren't really built to withstand huge G's without rolling over... thus, they recommend higher pressures to avoid that rollover or worse (extreme rollover resulting in blow out). A newbie losing a bit of traction is no big deal... they will be way off driving to the limits of even that lower traction properly.
So, once you've found the lowest pressure allowed (and presumably highest traction), then you start adjusting for over/under-steer by adding pressure at one end or the other. Assuming at that pressure (lowest without rollover) you are at max traction, then you want to increase pressure in back to reduce understeer and increase pressure in front to reduce oversteer. There also may be issues with tire squirm that will call for higher pressures.
The reason you might get various answers on how to deal with over/under-steer is that not everyone starts with tires at max traction. So, reducing pressure might be an option for increasing traction.
With all that said, there are certain cases where max traction occurs somewhat higher than "lowest possible without rollover". In particular, front wheel drive cars often seem to do better with really high pressures in the front tires. I have never really studied the reasons behind that as I have never wanted a front-wheel drive sportscar.
Hope that helps. |
neal (95spiderneal)
Member
Username: 95spiderneal
Post Number: 275
Registered: 3-2002
| | Posted on Friday, October 17, 2003 - 9:00 am: | |
i also get conflicting info ie. add air to increase traction at end of car thats slipping so add few lbs to rear to correct oversteer and few to front to correct understeer. that from tire rack.
also heard from several racers that should lower few lbs to increase contact patch for more traction which is obviously opposite of above. cant both be correct so whats answer? |
Crawford White (Crawford)
Junior Member
Username: Crawford
Post Number: 199
Registered: 3-2003
| | Posted on Friday, October 17, 2003 - 8:40 am: | |
I've had conflicting advise about tire pressure...
Some suggest to add a few pounds over recommended "street" pressure when tracking the car (makes for a stiffer sidewall?). Others have told me to deflate the tires a bit for more surface area and to compensate for the tires eventually heating up and expanding. This would be for a 328 with Dunlop SP 8000's. |