Recommended Boxster S Tire Pressures for DE

[George3]

[size=3]Hi,
I have an 2007 987 Boxster S that I am using for Driver Ed track events. I want to maximize my cars performance on the track and I’m unsure of the “correct�? cold and hot tire pressures for my car for this type of activity.   

The tires are Michelin Pilot Sport, 235/35/19 front x 265/35/19 rear.  


I’m told by the dealer that the “cold�? pressures should be 32 front x 37 rear. But, I’m not so sure this is the best setup for DE’s.  I’d like some opinions for this newbie.



Thanks!

George Busch

[/size]

[Tony356993]

George,

When I ran my stock Boxster when I started DE, I used to try and achieve my hot tire pressures to be what the cold tire pressure recommendation was.

i.e. for your situation hot should be  32 & 37.

This is not a perfect solution but it worked well for me in the beginning

 

[George3]

Tony,

Thanks for the tip.  What size wheels did your Boxster have ?

I've heard it said the lower pressures grip the surface better... I've also heard it said that higher hot pressures will reduce sidewall roll in hard turns and make the car turn in easier, with less understeer...  Is it a matter of the type vehicle?

GB

[Tony356993]

Here is an advanced copy of an article I am going to put in Der Gasser

What tire pressures should I run?

Probably the most oft asked question in the pits is: what tire pressures should I run? The most accurate answer to that question is: it depends. And that is what makes it so difficult to determine. It depends on a variety of factors including wheel size, tire profile, tire composition, tire brand, car weight, suspension setup, spring stiffness, track temperature and how hard you drive! No wonder so many are confused. I would like to explain some of the parameters, both objective and subjective, to help you make a more informed decision.

Let’s briefly examine what happens to a tire under cornering loads, as that is usually what you are optimizing your tires for. Under braking, the weight shifts to the front of the car and the front tires compress the sidewalls, spreading out the contact patch length-wise. As you begin to turn, the front wheels turn, twisting the sidewalls, and coercing the tire tread to turn as well. As the cornering load builds, the sidewalls flex more under the lateral forces, and the tread patch becomes distorted. The wheel will actually move over the tread, and the outer edge of the outside tire will roll under, with the inside edge rolling up and possibly lifting off of the road. The more this happens, the less grip that you have. How much the tire patch distorts will depend on a variety of factors, not the least of which is tire pressure.

It is the internal pressure which stiffens the sidewalls and supports the tire. Too much pressure and the tire will be firm, but will have less contact patch. Too little pressure and the tire will distort too much, also reducing the contact patch. The right amount will allow for as much contact patch as possible, with minimal distortion. The way to understand where to start is to consider how the variables listed above affect the optimal pressure:

Less < pressure < More
Wheel width – Wide < pressure < Narrow
Tire sidewall profile – Tall < pressure < Short
Tire type – Race < pressure < Street
Car Weight – Light < pressure < Heavy
Suspension stiffness – Soft < pressure < Stiff
Track Temperature – Hot < pressure < Cool
Driver Aggressiveness – Ragged < pressure < Smooth

All of these factors combine to determine what your optimal hot pressure should be. And I do mean HOT pressure; that is where your tires are operating. Cold pressure is merely the starting point at which to set the tire pressures when you start in the morning. The best way to figure out what you want is after you get your pressure where you want them, check them the next morning after they have cooled back down, and that will be your starting point. And this leads us back to the original question, what tire pressures should I run?

The ideal way is to take tire temperature readings. This will tell you how effectively the tire is working across the width of its tread. The outside and middle of the tread should be approximately the same temperature, with the inside usually being cooler. If the center of the tread is cooler than the outside, you need more pressure, and vice versa. Tire temps can also show the effectiveness of your camber and toe settings.

Many of us will just use feel to get the tires to close, and for DEs that is fine. I find that if my pressures are too low, the tire will brake well, but feel mushy and unresponsive in the corners. If the pressures are too high, then the tires feel crisp, but will feel greasy and slide too easily under both braking and cornering. Your best pressure and maximum grip lie right in the middle.

But many of you still want to know what pressures to run.  I hope that you can see that there is no one right setting.  It is something that you will have to experiment with.  That being said, there are ranges which most tires seem to operate in.  Slicks have the stiffest sidewalls, are run with the least amount of pressure, and can start cold at as low as 24 lbs, and increase to between 30~34 lbs hot pressure.  R compound tires need a little more, starting between 26~30 lbs cold and settling between 34~38 lbs hot and street tires need the most pressure, starting cold between 30~34 lbs and getting up to 38~44 lbs hot.  As I mentioned above, you will need to experiment to fine that exact pressures that suit you and your car.

Hope that helps.  I'll see you at the track!

The above is from Larry Herman. He's da man!

My Boxster had 18's

 

[George3]

Great article!  What profile were your 18's ?

[Tony356993]

I do not recall.

[Brian Minkin]

Michelin suggest that the Pilot Sport in a 19" size should run hot at 44 to 45 lbs when driven aggresively on a 3500 lb vehicle. This tire has different characteristics enginered then most high performance street tires.  I would start with a hot pressure around 40 and try increasing it to see how it effects the handling of the car. 

[George3]

Good advice, Brian.  40 lbs sounds like a reasonable place to start.  Would the 40 lbs be for both front and rear, or would you have less in the fronts?

[Graham]

George,

You ask a very interesting question...

My Boxster has 17 in. TOYO RA1's on it now.  I run them at 37 psi front and 39 psi rear HOT.  To achieve these #'s, I start the fronts at 24 and the rears at 26.  Sounds crazy but if I go too high when cold, then I am way in the 40's and the car handles for shite as Larry explained.

Watch the tire wear after each session and check the pressures every time.  As I have found out, if my tires are overinflated, the outer edge of the front tire rolls under and the car feels like I am snowplowing in the corners. 

It is a constant measurement, depending on the day temperature, how long you are on the track and how hard you are driving (plus other factors). 

Good luck!  The fun has just begun!

-Graham

[Brian Minkin]

George3 wrote:

Good advice, Brian. 40 lbs sounds like a reasonable place to start. Would the 40 lbs be for both front and rear, or would you have less in the fronts?

Even though you start with different pressures front and rear once the tires have warmed up from a session on the track they should all be equal pressure front to rear and left to right. I am suggesting you need to get all the tires to 40lbs when hot.