I always want my tires, front and rear, to grip at their maximum. If I need to change the balance of the car (i.e. dial out some understeer) I'll adjust the sway bars or shocks.

Funny, not 2 weeks ago at Mid Ohio I was struggling with getting grip on a coldish and damp track. The tires would not heat up, and the pressures would not come up. It seemed wrong, but I raised the pressures so that I would get 38/39 hot and the grip and balance came back, even though the tires didn't get fully up to temp. Makes you wonder.

 

which begs the question... Would you say that the same applies to the main thrust of this thread (.i.e. that tire pressure is an effective means of compensating for understeer)?

It certainly seems to be common wisdom, but I have also heard - less commonly - that tire pressure should be set only to maximize tire performance (grip) at ALL 4 wheels, not for the effects on handling, and that suspension adjustments are the preferred way to address handling. So I address understeer w front camber, reduced rear tow-out, PSS9's hard in front/soft in rear, and then adjust psi only to achieve consistent tire temps across the width of each tire independently - which means I may end up with 4 different settings vs. front/rear pairs. But perhaps I'm incorrectly ignoring this common sense wisdom and should experiment with front/rear psi differentials as well?

 

The more I study the less I know and become more confused.

This is the pursuit of a golf swing all over again.

 

Yep, that's the less common wisdom I was referring to...

 

IMO, it is one of may factors that can be adjusted to change the handling behavior of the car. However, the caveat: if you find yourself adjusting pressures more than a couple of psi to reduce understeer, you are also probably not helping the overall tire grip, and maybe you should adjust something else first.

 

I think that a lot of information gets passed around and quickly becomes "out of context". Can you adjust the balance of a car with tire pressures? Of course. Is it the preferred method? No, but if you have fixed sway bars and non-adjustable shocks it may be your only tuning tool, and a balanced car will usually be faster and more drivable than one with optimized grip and poor balance (i.e. excessive over or understeer).

 

This is an interesting point. What confounds me is that my tires were running temperatures that were consistent, even at the varied pressures. On the rear, at 33-34psi, I had consistent heat from highest to lowest, nice and linear. Same on the front at a more 'optimal' pressure of 38psi.

I have Motons, so I could adjust those to compensate, but instead, I used them to optimize the handling on the track, and the tires to control oversteer/understeer. I will try next time putting the tires at an equal or similar pressure and go full negative rebound back, full positive rebound front (or is it opposite?) on the Motons.

 

Thanks VR and Larry... that helps. I've been lucky in getting a great alignment setup from John Gladwell at Boardwalk, so fiddling w psi had felt like futzing with a good thing. Thanks for helping me confirm that; I probably need to stick to psi levels that simply adress consistent temps.

 

Yep..
I run my car using RA-1s at 38-39 hot. That means usally starting aroung 32 psi, but receintly I have been runing the car in session 1 at 32 psi cold all around. Then I bleed or add air to 38 psi at all 4 corners when hot. Then I let them be and don't change them. When they cool they are 31 to 33 psi depend on the corner of the car. My tire temps are pretty even front to rear and depend more on how many left or right turns.

If I have balance issues I first work on the driver and second look at sway bars.

 

i run more pressure up front, as well. the whole increase / decrease pressure to increase / decrease grip can be confusing. if you are above or below the design range of the tire, decreasing pressure will increase grip through increasing the size of the contact patch. it will also increase temperature. if you are WITHIN the design range of the tire, increases to tire pressures result in increases to the tire's efficiency, which in turn will increase grip. it will also DECREASE temperature. voodoo.

 

Understeer/Oversteer adjustments for dummies:



found it at the Tire Rack.
(passes the dummy test; this one, at least)

 

Yes, but can you totally separate the two? To some extent, how soft or hard your tires are changes the handling characteristics beyond just grip. Right?

I tend to run with just about equal pressures in the Boxster and it's pretty neutral but I have a lot of camber up front compared to the rear.

 

ive seen this too, i agree with most, except the first 4 lines. I can remember a track day where these NSXs were spining all over buttonwillow. they all had one thing in common, too high pressure. when they all dropped the pressures down to 32psi cold, for some strange reason, they stopped getting their cars so dirty! just take a car that is loose. you think upping the rear pressures is going to increase grip? tire pressures are and can be thought of like suspension springs. this is why loosing the bar, going softer spring can increase grip. softening the tire does this as well. I wonder if this is a misprint.

Mk