kw_1055

I drive a stock 997S with OEM Michelin pilot sport 2
front 235/35-19 hot 36 psi
rear 295/30-19 hot 40 psi
on the track in a DE event last week.
Outside temp. about 50 to 55

The rear tires are wearing even but the front edge on the passenger side shows excessive edge wear.

Is the reason too much understeer?
should I increase the front pressure to lessen edge wear?
should I decrease the rear?
Stock pressure is 34/40 cold.
So I keep about the 4 to 5 psi difference between front/rear on the track. Is that too much?
Is it time to adjust the suspension of the car?
Any suggestions?

smankow

you "chunkd" the tire - basically overheated the outside edge. It's primarily caused by lack of negative camber and also driving hard. I also think that your pressures were too high in the front. How did you manage to keep the rears at factory settings but not the front? What were the cold pressures?

also, the pic makes it look like you're approaching the wear-bars on the tire. How many miles are on them?


Steve

Bob Rouleau

Your tires pressures look pretty good. I liked 36/38 hot on the 997 I drove at the track but you are close. The higher rear pressure would tend to make the car understeer less if anything.
The main reason for edge (often called shoulder) wear is not enough negative camber. Hard cornering causes the tire to roll over and wear the shoulder of the tire prematurely. adding negative camber will reduce or eliminate the wear but yoou will find premature wear of the iside edge of the tires if you drive on the street a lot. A compromise setting for your car would be negative 1.5 degrees in front and negative 2 in the rear. A full track set up would be neg 2.5 in front and in the rear. I am not sure how you go about getting more negative camber on the front of a 997. Porsche has made it more and more difficult to add negative camber in front since it also reduces the tendency to understeer - if you do it, yoou will love the way the car turns in! OTOH for inexperienced drivers, understeer is preferred and oversteer is to be avoided like the plague. Lawyers probably dictate that the cars understeer. Even the GT3 comes set up to understeer from the factory. On the GT cars, you can adjust the suspension to reduce understeer, I am not so sure about the 987 and 997. You may need aftermarket camber plates or equivalent.

Best,

mitch236

Of course you could always replace the control arms with GT-3 control arms and then you would be able to get enough camber. I would avoid camber plates.

kw_1055

I drove to the track in the morning, so I set street driving pressure 34/40 to start.
The first run was cold, so I just lower the pressures by about 4 pounds to start the first run.
Then, I measured it hot after the first run and monitor them through out the day to keep it at 36/40 hot every run.

Tires are at the end of their lives. About 14000 miles, since it was a dry track, I decided to run these for one last run. Need new ones immediately. Track driving was about 10% of that, plus maybe 20% canyon runs. So I am still debating about doing the negative camber setup. What is your opinion of how much premature wear I can expect if I set it up with 1.5 degrees front. 10% life? more?

Crazy Canuck

What Bob says is true. I experienced what is happening to you before I added more camber.

You can install the GT3 bits as some guys have done but my mechanic elongated the adjustment area by drilling it out (proper terminology escapes me at the moment) to allow for more negative camber. It worked.

Crazy Canuck

BTW, I found 37 to 39psi HOT, with all tires at the same pressure, to work well. Above 40 PS2s get really greasy and are a handful.

Toyo RA-1s worked well too. I think I used 245/315.

kw_1055

Chris, do you mount the Toyo on 18" wheels?
What width do you use and what offset?
Do you drive them to the track and how long do they last for you?

VERBOTN

M:

10-4 on the GT3-LCA it is night and day and the best part is that they are plug and play.

Crazy Canuck

I used BBS LMs. I think I paid about $3000 for a set of 4.

18" yes. Much cheaper than 19s and there are more tire choices.


Rear LM143 - 18 x 11 Offset 56
Front LM099 - 18 x 8.5 Offset 56

You can drive the RA-1s to the track. They behave very similarly to the PS2 when new (unshaved) but stick really well after awhile. They last pretty long and are great in the wet at first. I only used one set before I broke down and bought the GT3 for a variety of reasons. Mooty uses them on his 997 GT3 RS. He likes them.

ervtx

I have never gotten 14K out of the PS2's even when used for street only! Consider yourself lucky if you're getting that much mileage. Regardless, the concept of throwing the last miles of a tire's life at a DE is kind of scary.

To think in terms of camber changes to increase tire life is sort of backwards. If instead you think in terms of improving tire performance (vs. life), you won't get to camber issues until you're ready to address overall handling and performance of the whole car.

As far as psi goes, invest in a pyrometer so you can adjust tire pressure to achieve consistent temps across the width of each tire. (hot in the middle: too much pressure; hot on the outside: too little pressure).

kw_1055

Maybe it is my driving style. I try to be easy on the brake and tire when I drive normally but push them on the track and twisty. I just tech my car last week and it still has 80% brake.

The wear indicator was ok before the track day. All the chunking of the shoulder was on the track that day, but I did put over 200 miles on the track that day. I do understand your point.

I know that neg. camber will wear the inside of the tire more on the street. I just like to know if it'll shorten the life of the tire by how much? Is 10% a reasonable guess?

Pyrometer is a great idea. Do you like the surface measure type or do you use the "poke" in the tread type?

4ng crcs

Looks like lots of left hand corners on a CCW track like Thunderhill (?)

I find my passenger side pressures 2 to 4 lbs higher after a session on that track cuz it is the side that takes the most abuse from 1,2,6-7-8,10,11.

Crazy Canuck

Driven hard I got 2000km (about 1200 mi) on a set of PS2s driven exclusively on the track.

Don't ask the lifespan of Cups.

kw_1055

It is Thunderhill. Good call.
I also tested 2 to 4 pounds higher on the passenger side but only after a long session.
So I bleed it back down to even after that run.
Should I keep it higher to lessen the roll of the tire?