Tire pressure

[Topless]

Originally Posted by san rensho

Why does Porsche recommend 7 pounds difference in tire pressure front to rear?

I've only had my car a couple of months and just recently statrted to push it in the corners. On 60-70 mph sweepers I noticed pronounced lift throttle oversteer. I said to myself, this is a Boxster, the mid engine should make the car very balanced and all, but it felt like an air cooled 911 when I got off the gas in corners.

So I put 4 more PSI in the fronts and it felt better. Then I went to 36 front and rear and now it feels great.

Is there a reason for 29 front/36 rear?

My best guess is ride comfort. The car feels smoother with 29F. I typically run 32 cold all around on the street.

Yes every car will exhibit throttle lift oversteer without active stability management... even a 63 Ford Falcon. It's a physics thing.

[jaykay]

Originally Posted by Topless

My best guess is ride comfort. The car feels smoother with 29F. I typically run 32 cold all around on the street.

Yes every car will exhibit throttle lift oversteer without active stability management... even a 63 Ford Falcon. It's a physics thing.

For sure.....even worse if you are in a sweeper and lift in a slide/drift, in damp conditions and baked tires.....it will over steer on the opposite lock right quick....don't ask me how I know this It does seem more er em violent with engine amid ships though

[jaykay]

Oh yes I like 31f and 34r but I am not racing the car

[stephen wilson]

I find this interesting, because I was just complaining on another thread about how my 987 Doesn't display any trailing-throttle oversteer. I actually find it a to be a helpful trait, and about the only thing that will kill mid-corner understeer. Is this another difference between a 986 and 987?

The "snap" oversteer is partially due to the mid-engine design, more rear weight & grip due to wider rear tires, and a lower MOI, but I think the biggest reason is the short wheelbase.

[jaykay]

Originally Posted by stephen wilson

I find this interesting, because I was just complaining on another thread about how my 987 Doesn't display any trailing-throttle oversteer. I actually find it a to be a helpful trait, and about the only thing that will kill mid-corner understeer. Is this another difference between a 986 and 987?

The "snap" oversteer is partially due to the mid-engine design, more rear weight & grip due to wider rear tires, and a lower MOI, but I think the biggest reason is the short wheelbase.

I was considering a constant throttle position and then moving to more open as in corner exit. Perhaps you are speaking to the corner entry phase. I too in the 986 can and do get understeer and have not yet properly reliably learned to correct as you have described. I am a beginner. While accelerating in a sweeper, I have noticed the car twich nose out...to understeer when lifting for traffic. It is really pronounced as if the body is flexing....and I can't feel that the rears were sliding, or can't believe it. Would it have something to do with my differential. If I get a chance I will try going back on the throttle to get the car pointed accurately

[stephen wilson]

Sorry Jay, I was more responding to the OP comments than yours. I agree that I can induce oversteer late in the corner with lots of throttle in 2nd gear. You have to be quick with your counter-steering, and straigthen the wheel quickly, or you'll get into a "tank-slapper". With neutral to mild throttle application there is a definate push, lifting off the throttle ( for traffic ) will tend to lessen this push.

[thstone]

With a mid-engine car where the balance is very close to 50/50, the tire pressures would normally be about equal to create balanced handling (neither understeer or oversteer).

However, very few cars are sold with balanced handling - most cars have understeer to avoid an average driver getting into a situation that they can't control very well (oversteer).

Thus, the 29/36 recommended pressure to add a bit of understeer to the handling.

[jaykay]

Originally Posted by stephen wilson

Sorry Jay, I was more responding to the OP comments than yours. I agree that I can induce oversteer late in the corner with lots of throttle in 2nd gear. You have to be quick with your counter-steering, and straigthen the wheel quickly, or you'll get into a "tank-slapper". With neutral to mild throttle application there is a definate push, lifting off the throttle ( for traffic ) will tend to lessen this push.

No worries we are just talking....I am just trying to learn proper car control. I have experienced a progressively more violent tank slapper just as you describe in the wet. It was a lot of work with no way out...had to let it spin and lockup once I thought I was going in straight line