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    Tire Combination Question?

    It is time to change tires. I was looking at the Michelin Pliot Sport Cup, 225/40ZR18 with an outside diameter of 25.2 inches and the 295/30ZR18 with an o.d. of 25.1 inches. It then came to my attention that Michelin makes in the Cup Series a 265/35ZR18 with an o.d. of 25.2 inches. This would also be a match with the o.d. of 25.2" for the 295's. I would have to buy 10 inch width wheels for the front. My question is what changes in handling would I expect to occur with 265/35ZR18 Cups in the front and 295/30ZR18 Cups in the rear? How would this affect the balance of the car? The 265 fronts have clearance. My current suspension/brakes are GT3R brakes (380 mm front/359 mm rears), GT3R sway bars with TRG adjustable drop links, JRZ Triple adustable racing coil/shocks w/ upper monoballs, the rest of the suspension has been replaced with GT3R components where applicable (lower arms, monoballs, camber adj. etc)


    Re: Tire Combination Question?

    CJ, I think you are in uncharted territory. Certainly you will get less understeer and probably even oversteer. But how much? It could be quite nice but it could also be a bit excessive. You hardly want to make yourself a rally car.

    Probably you could tune down the front end if you had to.

    Can you go bigger on both the front AND the back? This would make a little more sense I think.

    S.

    Re: Tire Combination Question?

    FixedWing, In the 18" Cup series Michelin does not make anything bigger than the 295/30ZR18. You did give me another idea. Pirelli, in the Corsa series makes a 315/30ZR18 which has an outside diameter of 25.44 inches and a tread width of 12.4 inches. They also make a 265/35ZR18 Corsa. It has an outside diameter of 25.35 inches and a tread width of 11.10 inches. Another match! Now I am really confused.

    Pirelli P Zero Corsa
    265/35ZR18 25.35" OD, 11.10" tread width
    315/30ZR18 25.44" OD, 12.40" tread width

    Michelin Pilot Sport Cup
    265/35ZR18 25.2" OD, 10.9" tread width
    295/30ZR18 25.1" OD, 11.6" tread width



    Oh so many choices. Which is the right one?

    Re: Tire Combination Question?

    Another piece of information. The tread width difference between the front and rear tires on the stock P-Zero's is 2.40 inches. The TW difference on the Corsa's is 1.3 inches. The TW on the Cups is .7 inches.

    Re: Tire Combination Question?

    It is really just a guess CJ but if it were me I think I go with the Corsa combo. I figure it this way:

    1) the Corsa has more overall tread area so probably more traction
    2) the additional rear tread area will aid straight line acceleration (just don't break the car in the process!)
    3) you are keeping a little closer to the standard ratios which means you will probably have to do a little less de-tuning of the front end. You really don't want high-speed oversteer on a street car!

    The only negative I see is the greater frontal area so probably slightly lower top speed.

    I just don't see a lot of difference between the Corsa and the Sport Cup. Yes, the Sport Cup is the flavour of the month on the GT3 at the track but you don't have a GT3 and you aren't at the track. I suspect that the greater tread area will make up for that small difference if not more. Also, these tyres respond to careful pressure tuning and also require certain temperature ranges to be at optimal. Each is different. So did the testers tune each one properly?

    My two cents ... and probably not even worth that this time as I've no first hand experience here (who does?).

    One question you must ask is what the highest sustained operating speed of whichever tyre you choose is given your loads. Remember, your car is heavier than a GT3. These tyres are designed to get nice and hot and sticky as quickly as possible. This isn't always ideal for high speed running (just as they tend to run at lower pressures which also isn't ideal for high speed running due to the additional flexing causing overheating). So make sure you know what the highest sustained speed is and at what pressures. You will probably want to run the tyres at higher than optimal pressures and then lower the pressures for "special occasions". I'm sure this won't be a problem in the USA though.

    Should also get an idea of the future supply of these tyres. Will they be around when you need to replace them? Might be worth getting two sets of rears if there is any doubt.

    All the best,

    S.

    Re: Tire Combination Question?

    FixedWing

    Taking info consideration my gearing and power, I don't believe these wider tires will have much, if any effect, on my top end. Time will tell. I believe either the Cup's or Corsa's will provide better handling, the question is which one will be better.

    I don't know if you have seen the October Porsche Panorama Magazine? They did a test called "18-Inch Track Tire Evaluation". Both the Cup's and Corsa's were tested. The vechile was a Porsche 996. Same temperatures, day, track, drivers, tire pressures etc. They did not use the tire combinations I am considering. The end result was the Cup's prevailed by about 3 seconds a lap. The Cup's also stayed far cooler. By as little as 40 degrees and as much as 70 degrees depending on which wheel. The Cup's were very impressive. There was much more information in this article. Right now, if all else was equal I would opt for the Cup's.

    I don't think there is any question a wider front tire on the 996tt will help handling. The question is how wide do I want the rear tire? Will the wider Corsa (315/30ZR18) become an advantage? Again I have doubts. The September issue of GT Purely Porsche features the new TechArt GT street S. This car is based on a GT2. TechArt is using street tires, but not the factory size 235/315's. Instead the chose the 225/295's. What made TechArt not use the 235/315 combination? Was it the added height of the larger tires? If so the Cup 265/295 I am considering is very close to stock tire height.

    Right now I am leaning towards the Michelin Cup's. I am hoping someone with some experience can help shead some light on this subject. If not, it won't be long and I will have some information to share.

    Re: Tire Combination Question?

    The Michelin Pilot Sport Cup's have a "Y" rating while the Pirelli P Zero Corsa's have a "Z" rating. I always thought the "Z" rating was a higher rating, but after reading some articles, I'm not sure. It sounds like the "Y" rating has a higher speed rating.

    "R" Tyres

    I have not seen the article but I've heard about it. There was a similar comparison recently in (if I remember correctly) Sport Auto. The Sport Auto came up with similar results but the difference was less dramatic.

    My question with both of these articles is whether the testers tuned each of the tyres to the correct operating temps to get maximum results. As I understand it, the Cup tyre is a colder tyre. It needs less heat. That means that it is at optimum more quickly. It is quite possible that the Corsa was never at optimum. Now with a heavier car maybe that situation would be different??

    My concern with high speeds is not performance. No difference there I would assume. My concern is with safety. These tyres are designed to retain heat more so as to get up to temp. This can be dangerous at sustained high speed use as the tyre can overheat. They also recommend lower pressures for the same reason. Again dangerous at sustained higher speeds (Michelin even recommends using standard pressures for street usage).

    So will standard pressures mean that the tyres don't get up to temp? Good question. If so then this favours the cooler tyre (the Cup tyre). But if more heat then this probably favours the Corsa a this is a hotter tyre.

    I don't think absolute traction at the back is such a big issue. Rather it is balance front to rear. Better to have the optimum tyre combination than to have to mess around with detuning one end or the other.

    Oh, the German tuners would never deliver their cars on "R" tyres simply because the manufacturer will not certify them for sustained high speed use. Remember that German rules require that the tyres be able to handle the top speed of the car.

    My guess is that there probably isn't a lot of difference between the Corsa and the Cup tyre in absolute traction and the better question is which will suit your needs better. But from everything I've heard the Cup does have a slight edge on the Corsa at the moment.

    Have you considered which might be the better in the rain? Or are you sure you will never need to think about this.

    S.

    Re: Tire Combination Question?

    hi cjv,

    Y = 300 km/h
    Z = over 300 km/h

    but as far as i know, the max. speed for the corsas is 290 km/h.
    thats why you`re not officially allowed to mount them on yout GT2 / GT3 / tt.

    regards
    rsv

    Re: Tire Combination Question?

    Can someone give me a link to the Pilot Cup tyre sizes.
    TIA

    Re: Tire Combination Question?

    LG1

    The site is www.michelinman.com . On the upper right hand cornor is search. Enter the word cup. It should take you to diffferent information about the Pilot Sport Cup tires.

    Re: Tire Combination Question?

    rsv

    All the information in the US shows the ZR rating as an older rating and the YR rating as the newer one. They say ZR is 149+ mph and YR is 186+. They continue to say ZR is for sports cars and YR is for the new exotic sports cars.

    Chad, I don't know if this helps

    A lot of Tuners over here in Germany contact tire manufacturers directly and sometimes are succesful in obtaining an official approval for a different (higher) speed rating depending on the car, tire pressure, rims, suspension setup, etc..
    Maybe worth a try to contact the tire manufacturers directly?

     
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