Tlaloc75

I appreciate that advice. I'm not driving to 10/10 like I would at the track. I am driving fast enough to load the suspension and feel chassis balance changing as I apply throttle inputs.

If I was trying to optimize lap times I'd use the approach you suggest and I'd really enjoy it. Even without trying to optimize lap times, if I had easy access to a track I'd do as you suggest.

In fact, I think I'll keep an eye out for large empty parking lots and if I get a chance I'll push it harder, autoX style with multiple settings changes.

Tlaloc75

Ok, I have some results from my last drive.

I started by bumping front tire pressure 2lbs - that put me at 36/38. I felt a small difference but it wasn't much. A little faster turn-in, maybe a little more grip at corner entry, no change in balance (that I could feel) mid-corner or at exit.

I then bumped the front PSS10 setting up 1 - that put me at 6/7. The turn-in felt a little more precise again, traction at corner entry felt about the same, maybe a touch better but not enough to say one way or the other for sure. The big change was in how the car rotated under throttle. Car rotated nicely with throttle input and I could balance the car so that front and rear were gripping similarly. At 5/7 it felt like my choice was more understeer or less understeer. At 6/7 it felt like my choice was minor understeer, transitioning to balanced grip and then with enough throttle, a touch of oversteer-based rotation.

Its not what I would have expected going into this, but that's the result I'm getting. For me, 6/7 is great fun but right on the edge of too harsh for the street. 5/7 is not as much fun, too easy to get the front to wash out. 5/6 is also fun but feels like it rolls more when pushing hard, especially off camber, the rear feels like its rolling more than I'd like.

Ok, that's what I've got. I think I'll stick with 36/38 tire pressure and 6/7 for my more spirited days, down to 5/6 or 4/5 when I need more comfort.

Hope that helps some others out there. I can tell there are a few of you that are dubious of what I'm finding, I'd just suggest you try the same experiments and see what you think. Write back with what you discover, I'll be interested to hear from you.

Happy driving!

Tlaloc75

And thanks mikemessi for the discussion, it was very useful.

mikemessi

My pleasure!! Always enjoy seeing another Rennlister experimenting and having fun.

Tlaloc75

I have a tire pressure question and since it has to do with chassis balance I figured I'd try asking on this thread first.

Why don't people run the same tire pressure front/rear or with more tire pressure in front than in the rear, in order to reduce understeer? Since the chassis understeers by nature and people run adjustable swaybars or wider rubber in front to combat it, I just wonder why tire pressure is typically run with more in back than in front?

I'm starting to experiment with this, for instance running 36 all around, and am curious about other people's thoughts and experiences.

il pirata

People do, from what I have seen generally people reduce the Porsche recommended tire pressure more in the rear than the front, to decrease understeer.

More weight.

mikemessi

Ideally you want to run tire pressures that result in optimum contact patch (no bulging or cupping ) to maximize grip. In general when chasing setup it's better to add grip where it is missing. Any tire pressure change to reduce understeer is most likely going to do it by reducing grip in the rear. If you reduce rear pressure to achieve this it will be temporary as the reduced pressure will increase heat and eventually increase grip. So you will go from no grip when cold to more grip when hot and have a constantly changing setup. On track pressures are started low knowing they will be too low at beginning of session then too high at end. Aiming for sweet spot in the middle.

mikemessi

You are better off adding grip to the front with a bigger tire or more camber or both.

mikemessi

Also, in my opinion due to it's rear engine layout, no car ever built benefits as much as the 911 from a little trail brake. Learning this technique (using it carefully at first) will completely transform your driving experience.

mikemessi

On the street, the trail brake is more a concept of coming off the brakes slowly to minimize the unloading of the front tires, rather than a true trail brake.

mikemessi

If you are looking to give the 993 the ability to power on oversteer without first tossing the rear around with a little trail brake and flick of the wheel, then the only way to do that is with more front camber and a stiff rear sway bar. Otherwise you will just unload the front and induce understeer.

Tlaloc75

This is great information, thank you!

What do you run for tire pressure? I tried 36/36 today and I can't say it felt any different than 36/38 - I'm guessing 2lbs doesn't really make that much difference. I'll probably run 34/36 or 36/38, maintaining a little more pressure in the rear to manage the weight difference.

mikemessi

I like 34/37 hot. So for the street that means 31/34 cold. I'm careful when first driving knowing I'm a little underflated. If driving in the rain you have to start cold at the hot temperature because they won't heat up and when underinflated there is cupping which promotes aquaplaning. This is the primary reason Porsche recommends such high pressures.

Tlaloc75

Good to know, thanks.

The reason I'm thinking about this now is that with the weather warming up, my hot pressures started going into the mid-40's, precipitating a pressure reduction. At that higher pressure the rear started feeling pretty loose and greasy so I began to question my entire tire pressure philosophy .

I'm going to spend the next few weeks tweaking cold pressure and measuring hot pressure to see what works best.

Thanks for the input!

mikemessi

Yeah if you get into the 40s you'll get bulging and a definite grip reduction. Low to mid 30s for front and mid to high 30s rear is ideal for contact patch.