mbb993

I could use some advice from the guru's out there. I have done a number of searches and got lots of great info but only more confused about what way to go here.

I have 17" factory cups on my 1995 993. Car is lowered with pss9's and is now driven to the track but have plans for a trailer.

I am considering tire availability, price and most importantly performance.
(I am aware of the need for the steering rack brace for use of 18" wheels on this car and plan to do this upgrade in any case.)

Appearance aside, if I wanted to have a dedicated track wheel/tires should I stay with the 17's or go to an 18" wheel?

Also, what is the maximum rim width/tire size I should use without having to worry about modifying the fenders etc. to avoid rubbing problems?

Thanks

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CWay27

My answers are toward a 964 but the thought is the same.

even though I am running 18's for the street, I decided to stick with 17 for the track. I had CUP 1's in 17X7 and 8. I put the 8 in the front and ordered 9's from tirerack for the back. Then I got a good deal on Hankook Z211 (compound 50) from Frisbyracing tires. I got 235 and 275. The rears are a bit taller but no rubbing or anything plus I paid 900$ for 2 sets. Did 1 DE on the first set and so far so good.

frisby still has the sale.

mhm993

In a perfect world it would be terrific to have wide very light 18's in 8.5's and 10's on the track, I think. I had those widths on my old 993 which was lowered to ROW. But if the choice is inexpensive cast 18's or the surprisingly light stock 17's I'd stick with the lighter wheel. I run 225 and 275 x17 on 7's and 9's with mpsc's and a bunch of camber and very low height, no worries. You can buy an extra set of oem 17" used wheels all over the mart for less than one quality forged 18" wheel, and it helps the tire budget, too.
On my old car, I had the cheap 18's, and the newer car turns in better and stops better with the lighter rolling weight. I always attributed the cracked windshield to the 18" wheels too.

my two cents. Marc

Edward

Hi Mark,

I ran with the stock 7 & 9x17 wheels for almost 3 years of time trialing and loved it! The majority of the time was spent on Victoracers in 225 and 275, and ran once with MPSC in 225 and (I think) 255. They work great, are light wheels, and never experienced any issues or felt like I was "shorted" in any way by having "only" 17s on. OTOH, I also never had my car on the track with 18s so who the heck knows what I "may" have been missing. The fact is my primary decision in sticking with 17s was cost: both of dedicated track rims as well as tire replacement. I believe with 18s, though, you just may have more tire widths and brands to play with; in 17 your choices are more limited IIRC (and it's been a while since I bought R-compounds in 17 since I am running 16s on my dedicated trackmeister ). Hope this helps you.
BTW, you may want to post this query on the Race forum and see what those guys say.

Edward

Greg Fishman

18's with the same tire compounds will be faster. All other factors being the same or similar that is.

Bill Verburg

I agree w/ those in favor of 18

8-9x18front 10-11x18rear

ZombiePorsche44

I'm really curious to hear how you came to this conclusion? are you talking hard data from what source?

In my years of Cup & Pro racing 911's, wheel diameter didn't have a whole lot of bearing on "Faster" unless you used it to gear down the car

ZP44

Greg Fishman

Yes I do have as close to hard data about this as anyone else. It is in the archives but here is a shorter version.
Edit: This was on my 993 race car which was very heavily sprung, not a soft street car.

I had a set of 17's and 18's with identical Hoosier tires (age and compound) except the 17's were a 275 width and the 18's were 285's. At Mid Ohio myself and a friend that is a pro driver did subsequent laps on each. We were both faster on the 18's. The 17's had a lot more roll and the car would take a "double set". First one was the set for the suspension the second was the tire rolling over, in some turns this was a significant event, IMO. The 18's didn't do this, at least not noticeably. I was considerably faster on the 18's, I want to say in the 1.5 second range, the pro's times were not as big of a difference more like a .7 second range. We hypothesized that he was better able to deal with the tire roll over where as I was a bit more chicken ****.

ColoradoMark

Greg, was the aspect ratio the same on both tires?

eunsulover

Volk Racing (Rays Wheels) make super light 18'' wheels, available for 993.
These are not well known among Porsche enthusiasts in the U.S., but a lot of drivers in Asia used them at the track on their 993/996/997. They are very strong and high quality. I think that Tirerack started carrying them.

ZombiePorsche44

Then it was your personal experience and not hard data from a tire or wheel manufacturer. Sidewall flex has never been a huge problem on 17's vs 18's unless your running a 17" street tire with a large profile on a race track. Also the slightly wider 18 gave you a hair more braking ability, especially at the end of uber fast straights.

I ran Hoosier's on 17's & 18's the last two seasons I raced and honestly couldn't notice a 1.5 sec improvement on 18's or I would have ran the 18's full time for the advantage.
Let's face it, any race driver would kill for one thing that can make the car faster by 1.5 sec a lap but I didn't have the same experience you did.

IMHO, I do feel the 18's are better suited for big tracks with ultra high speed sweepers (ie; turn 8 @ willow) and the 17's are better for bumpy (ie; sebring) or temporary street courses and short tight tracks.

ZP44

pcar964

No question, 18's are faster. Tires may be more expensive - but then again, Porsches aren't exactly the cheapest track cars to begin with. No reason to skimp on arguably the most important part of the chassis/suspension, the wheels and tires.

Greg Fishman

No, 17's are taller than the 18's. The shorter side walls in the 18's gave the car better handling.

Greg Fishman

There was a definitive difference. Hoosier was doing a lot of development at the time for the Grand Am Cup series on the 18's so maybe that was part of it. Either way we both had the same results of faster lap times. Also the car felt more stable and responded better on the 18's.

MarkD

less sidewall will do that... regardless of wheel size, right?