forklift

Hey Jeff (and other gurus),

After doing some research in the archives tonight (too much to do tomorrow to go out tonight), I came upon this thread: https://rennlist.com/forums/showthre...hreadid=115854 . What I am trying to figure out is which way to go on tires for my 964. I have 993 Carrera Cup wheels for my tracks that are 17 7F/9R and right now I am running Yoko 032Rs 235F/255R. I want to try the new RS04 Hoosiers (as recommended by one of my instructors and my technician), but I called Hoosier and they said they will not put the 255 17s in production until mid/late June. I see that you have run 225F/245R with the S03s with success. Can you elaborate? I have read that Hoosier tires are a bit wider at the same sizes.

I asked the Hoosier rep. about running 245s on my 7" rim and he said it is possible but does pinch and he knows a guy who races a 944S in SCCA who does this. Sound pretty crazy to me, as I know it was tough to mount my 235s on 7"s. Apparently a 275 on a 9" for the rear should be no problem. Even if this scenario is possible, is it advisable? Not only from a wheel diameter prospective, but also, do you think I will have rubbing issues? I think I read on another thread that you are going to 245/275s soon, if not already. And one more question for anyone who wants to jump in....common sense would dictate that the wider the tire, the greater the contact patch and that would yield more grip. Is this always true? I remember a tuner test on Peter Ferrel's RX-7 where he increased the rears to 275 from 225s (I think) and the lateral g's fell .04. If I would get more grip, and 245s on a 7" rim is not advisable (which I would think would be the case), this also gives me the perfect excuse to buy the FM10s I have had my eye on.....but I think there may be a wait on those as well.

What I think I will do is run with the 225/245s if you did like that, and just try the 255s when they come out.

Thanks,

Jim

Bill Gregory

Jim,

I wouldn't go with 245's on 7" rims - in your current brand, Yoko recommends 8's as the smallest width. I know several who run 245's on 8's just fine (9's are even better). 225's and 235's seem to work fine on 964 fronts, although I believe Jeff is running 245's in front. In the back, 255's-275's fit fine, of course wheel offset is important, and you have to watch for rubbing on the right rear oil line, the swing arms, and the inner fender wall towards the back, or around the 11 o'clock position. If ABS is a consideration, I believe the front to rear rotating diameters have to be within 6% of each other (the percentage is in the owners handbook, which I don't have with me).

FWIW, I use Michelin Cups in 225/255.

Robert Henriksen

If you're driving hard, any R tire is only going to last a few weekends. So look at it this way: It's not a permanent decision you're going to have to live with for years to come. And whatever tire you get, will increase the amount of experience you have with different brands/sizes/compounds. So you can turn into a guru like Jeff someday .

I would suggest sticking with 225/255 on your 7&9 wheels.

a) The extra 20mm wouldn't be put to the road surface efficiently as with wider wheels, so why spend the money?
b) it's DE, not racing, and
c) think how satisfying it'll be when you blow by some other guys who have more rubber, aero aids, fancy suspension, blah blah blah because you're focusing on the nut behind the wheel, not your next wallet-draining mod like the Viper drivers
d) If you can't ever catch the guys in c), then you have an excuse!

I was trying to talk myself into $3k+ 18" wheels so I could squeeze 245/285 tires on my car. Somebody sat me down and said, 'It's DE!!!' about 50 times until I finally got it. That was almost four years ago, and I'm so glad they did. Save your money, if you decide you're going to go racing, you'll need it

Adam Richman

Jim, its related but not exact; we run 225/50-14 R3S0x's on 6" wide rims all the time - I have been doing it for a couple years. There are plenty of guys in ITS doing the same w/ 245s on 7" rims. It doesn't hurt the tire. It does pinch in the tire to some degree (which some guys use for clearance issues if they don't have the right offset wheels). I have run 225s on 7" rims and there is perhaps a negligible difference between these and 225s on 6" rims but nothing to call home about.

earlyapex

Jim,

Wider tires do not necessarily give you better performance. Your car has to be able to get the tires up to their working tempurature and your suspension has to be properly tuned. I had a Miata which would run poorly on tires wider than 205's because I couldn't heat them up. The miata was too light. Furthermore, the tires contact patch in a turn may not be what it is in a straight line due to side wall flex. I personnally would avoid a tire size that may cause rubbing and thus cost you money to modify your car to allow you to stuff a wider tire under your fenders.

forklift

Thanks guys, I think I will take your advice and stick with my wheels and go w/ 225/255. I just don't really have the patience to wait until July for the S04s in 17 255. The funny thing is there are S03s in 255s still available, but all of the 225s are sold out (that I can find). ...and for the S04s, 225s are available, but no 255s. I don't want to mis-match.

I will probably go with 225/255 in either the RA-1s or the M Cups....unless Jeff did do well with the 225/245 in the Hoosiers then I may give that a try. By the time those are worn out the 255s will be ready.

Robert, thanks and I do like the idea of C in your post and saving $3k at the same time!

Thanks,

Jim

joey bagadonuts

Jim,

A couple points which may be relevant. Many of our 911 brethren run 225/245's--but on 16's. They're usually working with 6 and 8 inch rims, so that's not a bad fit and seems to perform well for their cars. I've seen 964 autocrossers run these sizes on D90's and while it's a different application, the results have been positive (for autox).

As for Jeff's future plans, I believe he's purchased some 8-1/2 x 10 x 17 Fikse's. These would easily accommodate the 245/275 combo so maybe that's what he was referring to.

I agree with most of the comments regarding DE vs Racing requirements. When you truly need those extra tenths, maybe then it's time to switch to the fat rubber. Also, an overly wide tire on a narrow rim can increase sidewall flex and tire rollover which is probably why the above mentioned RX-7 may have lost some grip.

0.02

Jeff Curtis

Yup, my new Fikses continue to reside in the guest bedroom, I've only opened one of the boxes...just to gaze at the unmistakable beauty that a brand spankin' new FM-10 possesses.

They are 8" and 9" wide, just as the Cupcars had.

They will have 245 and 275 series Hoosiers on them.

Jim, if your rear quarters came rolled, you can fit 275s no problem. The power to weight ratio of your RSA will handle the extra rubber w/no problem.

I have run 225/245 Hoosiers on 16" rims, 225/245 Hoosiers on 7" and 9" Cup II wheels and 245/275 Hoosiers on the same wheels. I would NOT use 245 series Hoosiers on the 7" cup wheels again, the tread section was not flat, kinda "bulbous" and they didn't wear well.

I think I had the most fun on 7" and 9" cups with 225/245 series tires, and it's simple why this is so...the 245 tires have a lower aspect ratio when compared to the 255s, effectively lowering your gear ratio (shortening your gears). The "tossability" of the car is far greater than the smoothness that the 245/275 combo commands.

Even the Hoosier dealer says he doesn't sell many 255s because of the aspect ration (255 x 45 x 17" vice 245 x 40 x 17") - a 16mm difference in diameter...while only a little bit, every bit counts...doesn't it??

If I were YOU, I would strap on a fresh set of Michelin Cups, in 225/255 fashion and run 2004 DE events on them...yes, they are a bit harder and don't provide as much grip as the Hoosiers - but you will get 2-3 times the use out of them when compared to the Hoosiers.

Besides, they are FAR better than the Yokos...so if you were having fun on the Yokos, just think of the fun you'll have on them!

forklift

Excellent, thanks! It looks like I will have the Cups in my future. Obviously you prefer those over the RA-1s. My only concern w/ the Cups were complaints of being squirrelly at low temp., but I guess if I am very careful with TWO warm up laps, I should be fine. I like the "FAR better than the Yokos" part, and what this will do to for my lap times (although I just started timing).

Thanks!