ypshan

I need recommendation on autocross tires that will fit the winter wheels. 225/40 R18 in front and 265/35 R18 in the back. Here are the considerations.

- I already have a set of summer wheels/tires and a set of winter wheels/tires. I can replace the winter tires with autocross tires during the summer and don't have to buy any more wheels.
- With narrower rear wheels, the car will have less understeer and be more "balanced" during autocrosses
- I can use street summer tires for every day driving and tracks.
- This allows me to get the most sticky autocross tires there is and don't have to worry about milage.
- Since I am a novice driver, using street tires on the track gives me more feedback and more learning.

I've looked at Sports Cup for autocross use but it doesn't seems to work very well due to the long warm-up time before it turns grippy. I'd like to use other tires that are sticky right from the start.

Any recommendation for tires that will fit the winter rims? Sizes? thanks.

Joe Weinstein

If you want to win at autocross, you have no option other than
Hoosiers in the AS03 compound. You want:

P245/35ZR-18
P285/30ZR-18

You want high tire pressures, around 43 front, 46 rear.
You want decent camber, at least 1.5 negative, front
and rear.

Joe

offroadr35

i agree, that's pretty much the bottom line. Pretty soon there will be a new compound that should be even better. Also the new Kumho V710s look pretty awesome but they are not available in those sizes yet.

-Steve

Joe Weinstein

Hi, and thanks Steve. Actually, what's coming isn't exactly a new
compound, but a different carcas construction with steel belts. The
tread compound will be the same. They are the AS04s, which should
be available in Spring in our sizes.

ypshan

I can find lots of tires that will fit the front stock wheel without problems.

When it comes to the rear, it's a lot harder. I was hoping that the winter wheels being smaller can give me more choices. I guess that's wishful thinking.

One question, why wouldn't one use 225/45 R18 tires in the front? 245/35 tires are a lot smaller in diameter.

Joe Weinstein

You have to run same-diameter tires front and rear. Those Hoosiers
are the only appropriate Hoosier DOT autocross tires that suit your
wheels and are same diameter. The AWD aspect of the 996tt greatly
limits the tires you can actually run. If you had a GT2, it would be
different.
Joe

Zippy

Joe:

When you say, "You want high tire pressures, around 43 front, 46 rear." I assume you mean hot?

Mike

Joe Weinstein

Hi. In autocross, you start cold at the pressure you want, and
at the start of the next run bleed off pressure if needed to maintain
your desired level. I believe you would just waste a run and possibly
unnecessarily chew up the outside edge of the tires if you tried to
get the pressure correct by running it hard. In road race, it's different.
Because you're out there a long time and you have to go slower to start,
and let the tires warm up to their running pressure. Autocross is more
like a knife fight. You can't dilly around or hold back. You have to go for
the throat *right now*.

ypshan

I checked out the Hoosier website and found that they recommend:

8.5-9.5" Rims for the 245/35 ZR18 and
10.5-11.5" Rims for the 285/30 ZR18

http://www.midatlanticmotorsport.com...dot_radial.htm

Since my winter rims are 8" front and 10" back, would I be able to use those safely?

Joe Weinstein

I forgot you're using different sized wheels.... They will probably
be Ok, but if you want to go well in autocross, you're best bet
is to use the full-width wheels.
There is another tire option! The kumho 710s are coming out in
Spring, but I've recently seen some excellent autocross competitiveness
with 996tts running the

Kumho Ecsta V700 rim size
225/40R18 7.5 - 9
285/30R18 10.0 - 11.0

ypshan

Thanks for the info.

If you have your choice of autocross tires between the 3 below, what order would you place them?

- Hoosier A04
- Kumho V700 or V710
- Michelin Pilot Sports Cup

Joe Weinstein

It partially depends on the surface. On dry sticky warm concrete I would
say Hoosiers would win, but we don't know about the 710 or the AS04
yet. The AS03 is very light, and more fragile, with zero steel.
On looser, worse or wetter asphalt I've seen the kumho 700 beat
Hoosiers. Kumhos are also cheaper. The Michelin is a roadrace tire, so
it isn't ideal for autocross, unless you have a partner (or 2) to heat
them up for you.
The kicker is your requirement for a 10" rear. I would go with the
Kumhos. The AS04 and 710 seem like they are converging towards
each other. The AS04 gets some extra stiffness with the new steel
belts, and the Kumho goes to the nearly-slick minimum tread, like
the Hoosier. These two seem to be more competition oriented than
any other street-legal alternative. The Hoosier will probably continue
to provide a stickier, shorter-life autocross-specific compound, so on
optimal surfaces, it will have an small edge, maybe, at a price.
Joe Weinstein

Greg Fishman

A 996TT is not an ideal Auto-x car. Get full size wheels and tires you can take on the track. You will soon forget about auto-x.

ypshan

Greg,

I realize that. Boxster is a much better Autocross car. My purpose is to combine both autocross and tracks to speed up my learning.

To be close to the limit on the track, I need to be able to feel of what it's like. Autocross gives me a safe way to feel the limit of the car in a short period of time.

Greg Fishman

I understand what you are saying but don't 100% agree, but in any case I wouldn't use a auto-x specific tire, they will cause you major issues if you take them to a track.