Sorry for the long winded post, but this is driving me insane. My problem is the only sizing advice I can get here in Aust is from the distributors who basically recommend what they can most easily supply. My car is a 550 Maranello, 3300lbs (1500kg's) 560hp 53%/47% weight distribution. I am running 11" rims all round. Michelin recommends 27/65 front(270mm tread width, 650mm diameter) 27/68 rear. The 27/65 is the recommended front fitment for Porsche GT2 race cars and the 27/68 is the recommended rear fitment for 996 and 997 Cup cars. Pirelli recommends 305/645 or 305/660's all round, has a greater variety of compounds, but the local distributor is terrible at holding stock, currently only having the 305/660 in a 3-4year old endurance racing compound, which they have 90 sets of they are trying to offload cheaply. BTW the tyres are pretty much identically sized width wise, Pirelli seems to measure sizes from sidewall to sidewall, where Michelin measures tread width. I am leaning towards the Michelins because of the lack of availability issues, but the 27/68 being recommended is almost 5% taller in gearing than the Pirelli 305/645; 680mm diameter V 645mm diameter. At my fastest track, I don't even use 6th and short of changing diff ratio's, which I am loath to do, really don't want to lose acceleration by effectively lengthening all my gear ratios by 5% using the taller tyre. As an alternative, I am thinking of running the 27/65's all round, the 27/65 was the recommended rear for the Porsche 993 Cup cars, which is interesting as the local Michelin guy says the 27/65 is designed as a front, not a rear. Is there any tangible benefit of running the taller rear that I am not aware of? I know a number of race cars do use the staggered height configuration, even though they run the same widths front and rear, but don't completely understand the reasoning. I do know that lager diameter tyres give a greater contact patch which results in more traction and also have greater load capacity which is a real issue in GT1 etc spec cars that run predominantly rear biased downforce that is 5X what I run. I am trying to find a tyre combination to develop the car so I can compete in State and eventually National championships, so I need to make a decision and stick to it. Thanks in advance for any help you guys can provide. Stephen
A taller tyre gives better braking modulation. A taller tyre obviously turns less times per lap etc, meaning it thoeretically lasts longer. A taller tyre has greater side wall flexibility, which is NOT controlled with a shock absorber, therefore theoretically handling could be compromised. Typically, a taller tyre makes a good drive tyre, and a lower tyre makes a good steer tyre. In Australia... for speed, use Dunlop for supply and support and a really good all round tyre, that's nearly as fast as a Dunlop, use Michelin for no reason, use Pirelli (shame, but supply support is NIL) You need a short crown/pinion at least, and also a closer 4th/5th/6th gear set. You only need 280km/h max at ANY circuit here, and 250km/h would cover it for most tracks except PI and Bathurst.
Are these 18" wheels? If so, then I would get Hoosier VRL 305 30 18's from Bobby Archer (German Motor Works) in Dallas/FW (817)877-1772. They are made for Dodge Comp Coupe which is a little lighter and more HP. You can get a set of scrubs if you want to try them out one time. These are race tires only, if you want DOT slicks then I would go with Hoosier R6 from Tire Rack. A less expensive but less capable tire is the Toyo. Michelin's suck!
Jim Thanks for the tip, yes wheels are 18's, but DOT approval not required, just a pure racing slick. We don't have a lot ofexposure to Hoosiers over here, except for the DOT spec R3S04-05, which I have used in the past, before I went to race only requirements.
I guess that's true but does not make any sence to me. I have run goodyear and pirellis and michelins. Sources I read says the performance of tire goes dunlop/pirelli/mich. I was always taught lower profile was better. Lower sidewalls tend to be stiffer and have all the +/- of that. I also like aceleration any way I can get it even 5%. If you are going to develop on a tire anyway then you could tune out for either tire in chassis rake and rollbar so I'd just go for the lower profile. I have also had better tire temp stability with a lower volume tire. More air more expand contract even with nitrogen. I'm very tail heavy 348 gutted so my front is weightless. All my problems are in the rear 245 645 18f and 305 650 18r and I am always fussing with tire pressure in the rear. A combo of my bad driving, varied abient and track temps, road irregularities, and maybe tire volume and I'm always screwing with air pressure. Porsche does have problems due to rear weight bias of blowing apart some tires since the rear tires are the ones that usually need to be managed on these cars. Racing porshes are much lighter than the 550 too so eventhough you are near 50/50 perhaps you could overload a tire designed for front use. But I doubt the reps statement...never heard it on mich and if a 993cup could use it I don't see a problem. Only time I heard an issue with that was 275 hoosiers on porsche 911 were a no no by the manufacturer. At 3klbs I would think you would be managing front tires. Sounds like part of your development needs to be cutting some weight out of that car. I have run a 68 mich and did not like them. Either I had a mental problem or I really did feel a differnece I'm not sure. It probably would have been better if I readjusted my chassis rake but I just threw the tires on drove them and could not wear them out fast enough to get rid of them. Same goes of some free 680 pirelli rears I got scrubs off a 360C. I hated those too maybe I'm mental.
The came apart in Turn 13 and ruined the race for all time! Duh!!! Also, the guys running them (PSC's) in the Viper Days events get smoked by the Hoosier drivers!
I don't know who your sources are (prob Euro car mags...who don't usu test US products), but you should try some Hoosiers sometime. Get some and tell me what you think. Image Unavailable, Please Login
YIPES! Sorry to hear that. Have asked on a few boards about the Mich Pilot Cup, and talked to guy who were on track with them, and they all seemed to be very positive about them. Seems MANY guys swear by Hoosiers of course, but the Pilot Cup are said to last a bit longer and for broke guys like me.... It is like Hoosier Heaven at various tracks days indeed. Now if only those magic lotto numbers came my way...
Yeah...I was so impressed with Hoosiers I forgot I've used them too. I'm even less impressed with hoosiers dot's which I don't use period. I had a bad experience on them once. Image Unavailable, Please Login
Looks like it ?chunked? Two guys had that same problem with new Hoosier R5's two weeks ago on track. Amazing to see over $1k of rubber only last about 30 minutes and then CHUNK. Insane...
Didn't I just read in another thread that you are a scrub user? Maybe you get what you pay for! I am not knocking it, it's just that I don't see how you can fairly judge a tire unless you run fresh ones. For all you know, the tires you bought used were run a half dozen times and sat on a shelf for a year. It looks like you run them to the cord, which is typical of scrub users (again, I am not judging you), but why keep the trash? No used tire depot in your 'hood??
Winning races and swinging a big dick are not my priority. I'm an old guy out to have fun. If I win great. Fresh scrubs been there done that. Honestly at my level aside from the few golden laps fresh rubber is not worth 4 times the cost. The 348 belongs in no series and is not competative. If I was doing large field 944 spec or something like that then fresh rubber by all means. I got a tire changer and swap at will. I will burn a set of rears in two days on the track to the cords and swap out. I do believe you get what you pay for. and I have not been impressed by new hoosiers any more than new pirrellis.
Billybob, More like 6 times the cost, but you don't put used oil or brake fluid in your car, do you, even at pennies on the dollar? I think the point of this thread is what size slicks to run on 11" wheels, and I offered what I thought was the best option out there for the 550. I guess we have gotten off track. What do you think is better than the Hoosier VRL 305\ 30 for a 550 (scrub or new), and why?
You have got to be kidding me...do you just like to hear me talk? O.K. ... Pirrellis bobwoodman tires New 362/tire, scrub 85 I say pretty close to 4 times. Most would agree that a scrub slick still has higher traction than a dot race tire at 200 for a kumho dot which has more grip than a street tire. That means the most grip/$ is in a scrub. A scrub tire does not hurt your car. all it does is lower your grip relatibve to a fresh slick yet has higher grip than a dot and is cheaper than both. Do you sell fresh rubber? Using old brake fluid is not comparing aples to apples. If you don't see why I don't want to ride in your car. And finally, lets get real on what tire is better. Why not we just discuss why a corvette is better or worse than a ferrari.
Uh, Pirelli has only one "R", and you should be able to get scrubs for $50 ea. For those who don't know, performance drops dramatically after a certain number of heat cycles, which differs in each brand. The Hoosier VRL's are good for about 12-13 cycles on a car similar weight and HP to a 550. Do Pirelli's beat that? I don't know as I don't run Pirelli. I have used Pirelli's and find that I have to add a lot more weight to get them balanced (like 8 oz v 1-2 oz), and had a slight vibration. Not fun at 150 mph. I am not personally able to compare these two tires head to head since I have never had a pair of each to swap and use on same day in same conditions. No, I don't sell tires. I buy them, and only trust my life and my car to the best tires I can afford. I feel fortunate that I can afford to run new tires. If a person can afford it, I think they are crazy not to do the same. You run at the front of the pack not the rear, have more confidence in your car, esp at the limits, and will basically get a better and safer ride. JMHO
Please post your source of $50 scrubs sold as the typical 90% to full tread listed in all the racer rags. Inquiring minds want to know. In fact if you can get them for 50 I'll buy them from you for 60 and I'll take a dozen so that's 120 bucks to you for making a phone call. What do you say? I have never seen any tire need 8oz to balance and I don't beleive it. The italians have crap QC but they are better than the chinese. Many tape weights come in 1/4oz increments because machines today can balance that well. You can still get heavier tape weights that are not as long but 1/4oz is like a standard. When is the last time anyone has ever seen this inside their wheel? This is 2006 give me a break. You need a new tire guy. Image Unavailable, Please Login
