hdemas

I'm thinking about switching to slicks from DOT-R tires and just wanted to get any experience or warnings anyone may have with respect to fitment. I'm currently running 235/40 R18 in the front (25.4" outer diameter) and 285/30 R18 in the rear (25.1" outer diameter). I was looking at the Hankook slicks: 240/640 R18 for the front (25.4" outer diameter) and 270/580 R18 for the rear (27.0" outer diameter). My two primary concerns (both centered around the larger outer diameter of the rear slicks):

1) The effective gearing will be taller in all gears. Is the difference too small to really worry about it or is it really going to slow the car down?

2) The car is extremely low and on race springs...think 993 cup car. The ride height will likely need to be adjusted to deal with the taller rear tires in the rear. Is this well within the adjustability that exists or will the car have to end up really high in order to keep the rears from hitting the insides of the rear fenders.

Can anyone with experience with these or other similarly sized slicks share any experiences? Many thanks.

Harry

FLA997

FWIW, I am currently running the Hoosier "leftover" Rolex Series Grand AM GT Racing slicks in 245/645-18 and 280/640-18. The front are more equivalent to a 265 DOT tire, and the rears are just about 285s in repect to DOT sizes. These tires are a bit taller (see Hoosier site) than say, MPSCs or R6's and I cant tell any difference in gearing...although I do have a RS Gearbox. I have no ABS issues either.

No rubbing issues on 11kg and 14kg springs. If your car is at Cup Height, like Bill V's car, I would think your ride height, as you said, would have to be adjusted.

Unfotunately, I have no experience with the Hankook slicks you mention.

Steve Weiner-Rennsport Systems

Harry:

I've not used Hankook slicks put I have plenty of experience with the others and I can tell you that if you make the switch, you will need more suspension than whatever you currently have due to much increased grip levels,...

The difference in those diameters is significant and it definitely alters your gearing and not in a good way.

race911

What times are you running? I *think* my yellow car is good for sub-2:00 @ Thunderhill (full track) on fresh Hoosiers. Extrapolate to ~1:47 @ Sears, ~1:38 @ Laguna. (Understand this is a theoretical in my head, talent-wise I'm a couple seconds shy.) So when I compare dealing with slicks on the Radical v. "R" compound stuff, unless you're racing I kinda get to the "what's the point" end of the discussion.

993_Pilot

Keep in mind that 25.4" diameter in the front vs. 27.0" diameter in the rear, will give you about a 6% difference and will cause the anti-lock/anti-skid function NOT to work, in addition to the taller gearing.

993inNC

Do it and you'll never go back I run "leftover" Yokohama slicks also from Grand Am racing and love them. Usually they are at best, scuffed in from qualifying sessions and are guaranteed to have 70+ % on them or better. They are a bit taller than a DOT, but I have no issues at RS height +/-, and it totally transformed the car even with PSS9's.
Oh.......... and they're a fraction of a new slick's price

avidtest

I did an AX last weekend and Mark Kinninger (from Black Forrest Porsche in S.D.) and his son Erik had a newly purchased 993 (from our own RL'er David Ray). They ran brand new Hoosiers for the first couple of sessions (not sure if they were R6's or A6's) and then switched to some used slicks they'd picked up at Big Willow (not sure of brand or model - sorry). Even though they were worn, Erik was 2 seconds faster right off the bat than he was on the new Hoosiers. And he was already fast.

I know AX is different thanl continous lapping, but still, the difference was significant.

jaholmes

Ok, so what are the negatives to running slicks.

Kika

well, if you get caught in the rain....LOOKOUT!

993inNC

...and you can't leave the track with them on the car......

jaholmes

Is pulling too much G's and causing too much stress on the chassis an old wives tail.

Harvey Yancey

I've been running used slicks for about 5 years and have never looked back. I have ran Yokos, Dunlops, Michelins and Hoosiers. I found the Yokos to be the best with Michelins a close 2nd. YMMV.

BTW - Running slicks in the wet is a great way to practice car control ...

hdemas

Thanks so much for the very helpful replies. I will look at the other brands of slicks as well. I will also have to look at the front/rear diameter differences for the other brands and see how they compare...I don't want anything that will flip-out the ABS system.

Ken...At Thunderhill I can do a 2:05 on MPSCs with the car weighing in a little over 3000lb (without driver). With less weight, fresh Hoosiers, a 3.8 liter motor and a few of the other modifications Yellow Zonker has that my car doesn't, getting down to 2:00 or a bit under that should be possible though not exactly easy.

Harry

993inNC

Dell (LVDell) and I did that at CMP the last time we were together (late last year). OMG we had SOOOOO much fun. Its amazing how well a slick performs in the rain. We were, I think, the only ones out there and it was the coolest. And of course neither ran our cameras since we figured we'd be in after one lap.....nope. We stayed the entire session, to much fun!

38D

I personally would not run slicks at DEs. All you end up doing is catching people in the turns that much faster. It gets old real quick. Since I only have slicks with the cup, I'll run the crustiest ones I have for the occasional DE (like 25+ heat cycles). But to purposely upgrade to slicks just seems like a waste. If you really want to get better, go racing... you'll improve 1000% more than trying out slicks.