dave morris

When I got started, the "optimum" (meaning lightest, cheapest, fastest) wheel set up for my old '84 911 was the 16" Fuchs 8" (off an '86 951 part # 951 362 117) and 9" (part # 911 362 119). At least that's what I thought.

Now, it seems lots of people may disagree. I believe the range of wheels now being used on D and E cars in PCA club racing (my specific area of interest) run from custom 15" wheels (cars prepared by Jim Buckley) to CCW 18" wheels (cars prepared by Dan Jacobs). The shop that built my current D car used CCW 17s (8s&9s).

So ... my question is ... what is currently considered the "optimum" wheel set up on PCA D/E cars? I know there are lots of variables. I'm assuming cost is a major variable (or else we'd all be driving 996/997 cups). I can't think of any other class of cars that fields such a wide array of wheel diameters. I'm assuming they are all still 8s & 9s but I'm not even sure of that either. I'm guessing the Fuchs wheels are still the lightest but that may be incorrect. Don't know what Jim's wheels weigh. I'm assuming the 15" might be quicker on a short track and the 18" on tracks like WG or Sebring. What are the relative strengths/weaknesses of the various options? Which variable leads you to prefer which wheel?

Any and all thoughts are appreciated. Thanks.

arrivederci

My understanding is that the 15's will effectively shorten your gearing, making you faster pretty much everywhere. The ticket is also still 8's and 9's...that's the max width rim you can run. Custom offset wheels will also let you run more tire (235/245 front and 275 rear). Some say tires that wide aren't necessary.

Sean F

Hey Dave
If I were to do it over again, I would buy CCW 17's 8/9. I think those 15 inch dirt track wheels need to be banned or declared a prepared mod. The 18's on my car are great for the long straights, but the guys with 17's seem to come off the corners much better than my 18's. No scientific evidence.

Sean

paradisenb

I run 17" wheels for R6s and 16" for rains. They fit and don't rub but it's tight.

FredC

Buckley makes the lightest wheels money can buy and I believe that his wheels make our cars noticeably faster. One issue with the 15s is that they will make you shift a lot more and 915s don't like that... (more shifting also means higher chance of money shifting especially when you operate under pressure)... The other issue is that those dirt track wheels are probably not made to endure the lateral loads of R compound on black top... but that it just me saying it.

I agree with Sean that 18s don't appear optimal out of turns (the toe of the boot at the Glen is a prime example).

I think 16s and 17s are a good compromise, with 17 x8/9 giving you the ability to run the preciously fat 245/40 and 275/40 tire combo... 16s won't allow you to run a tire that wide in the rear...(I believe that wider is better.... within a certain range of course).

dave morris

Thanks guys for the responses. My question is an honest inquiry. I'm not trying to draw attention to any particular set-up ... and I'm not advocating banning anything. Just interested in understanding the issues.

I understand Jim Buckley is very fast. I know Fred and Sean are. I'm sort of hoping for an apples to apples comparison of lap times. For example, would Driver X be just as fast on 15s and 17s or 18s on the same track under otherwise identical circumstances? Has anybody actually compared the two?

I'm also wondering if the 15s would simply run out of rpms on the back straight at the Glen?

FredC

There was a guy who ran 15s this year and 17s last year at the Glen. He was much faster this year and i could not pass him in the enduro... (until he missed a downshift). I think one (as in driver X) could run faster times with the 15s, but lots more overall skill would be involved because of the extra shifting (my opinion and only my opinion...).

Running out of rpm/gear at the Glen????? No way, you would not even run out of rpm/gear at Road America between T3 and T5. It comes down to more shifting again. I haven't had to use 5th gear in my car for a long long time.. (except to conserve fuel during the last few laps of the enduro at WG this year). With the 15s, i am sure that i would have had to get to 5th gear before T1 and perhaps even the bus stop.

paradisenb

Fred, what size wheels do you run? I know Sean has/had 18s.

Re: "I haven't had to use 5th gear in my car for a long long time.."

I have 17s and must shift into 5 on the back straight at Road Atlanta. 4th is enough everywhere else.

Sean F

Fred runs 17's and he is clearly stronger than me in places coming off corners. I think I'm faster in the esses on the 18's at the Glen. The 15's make a big difference I have reviewed video of starts from the Glen where guys were running the 15's and it's substantial just going by how they pulled me.

Astroman

I have 17" 8s and 9s with 245/275 R6s. My previous wheels were 16" 7s and 8s with 225/245 tires. Hands down, without a doubt, no question about it, I'm faster on my 17"s.

The larger rear wheel diameter allows me to use 2nd gear in places where I lugged in 3rd (Carousel at Mid Ohio for example). I just barely hit my rev limiter in 4th gear at the end of the back straight at Mid Ohio. I haven't used my 17"s at Road Atlanta but I'm pretty certain I'll need 5th there (but my rev limit is only 6500).

Gary R.

Not sure why 17's and 18's would be any different at all other than possibly weight. I did a comparison of all Hoosier sizes available for our cars in 15, 16, 17, and 18 last year and the rolling diameter (effectively the gearing) was almost identical on all but the 15" tires (which were substantially different).

Found the email - comments are just MHO...

From Tirerack

245/50ZR15 Price:$217.00 - 24.8" Rolling Diameter
275/35ZR15 Price: $244.00 - 23.0" Rolling Diameter - They don’t offer a /35 for the fronts to match, not sure that would be good?
275/50ZR15 Price:$244.00 - 25.5"Rolling Diameter

245/45ZR16 Price:$226.00 - 24.7" Rolling Diameter
275/45ZR16 Price:$244.00 - 25.5" Rolling Diameter

245/40ZR17 - 24.5"Rolling Diameter
275/40ZR17 - 25.5"Rolling Diameter

245/35ZR18 - 24.7"Rolling Diameter
275/35ZR18 - 25.5"Rolling Diameter

Now seeing all this it appears that there is only one wheel/tire combo that would actually make any difference in overall gearing on our cars, and that would be to run the 15” wheels in the rear with the 275/35ZR15 R6. If these figures are correct the 18” fronts are actually .1 inch SMALLER in rolling diameter than the 15’s due to the lower profile tire available. If you could get a /35 in a 245-15 it would be approx. 22.7”… There is apparently no advantage in going to 16 or 17”wheels using Hoosiers, and you have to wonder how long they will continue to produce 15’s in the /35 profile..

paradisenb

If all combinations have similar ODs, the only difference would be weight.

How many ozs could that be? Did you check into the tire weights, Gary?

FredC

Spoiler. I think dave should put 20 inch wheels with spinners on his car.

Seriously, I don't think we can discount the impact of side wall dimensions (fatter sidewall is more progressive until too much) and wheel weight. Also, I did not know they made a 275 in 16... Nobody runs that tire I wonder why.

Chris M.

The rev limiter on the 3.2 cars is a disadvantage and makes tire choice more crucial. You are faster now on the 17s but you're just a better driver. I think you could run the same times on the 16s, especially at Putnam.


The fastest guy in the country that I know of in D or E runs 15" wheels with 225s all around, which have a 22.9 inch height. He does not use 5th gear on the back straight at Road Atlanta, mostly due to a 7100rpm rev limit.

Not all 15s are the same. I run 225/45 and 245/50 (they don't make a 245/45 or 245/40 15) 15s on 7/8 Fuchs but the 245 is 2 inches taller than the 225 so the gearing advantage isn't there. I will try the 225s all around at some point as I think it's the best setup. On 205/50 225/45 RA-1s I was only 1.7 seconds slower than I was on my Hoosier 225/245s so I think a 225/45 rear Hoosier would be fastest.

The other advantage to 15s besides gearing is the weight. Even the lightest 17" wheels you can buy are at least 5 pounds heavier per wheel than 15" Fuchs. I just don't think the giant rubber is much of an advantage, especially on these cars which don't have much power. Astroman (that bastard) can already pull me on the straights with his monster 17s, so with a lightweight set of 15s with better gearing he would be even faster.

Sean F

other than the 15's, rolling diameter is the same so something else is in play - might be weight (wheel and tire?). I might just borrow some 17's from someone at a DE and see what happens running them back to back.