Track Tires Question

**K-Man S** · #1 (**permalink**) 03-17-2006, 04:21 PM

I was thinking about getting a set of Michelin Pilot Sport Cups for my 18' wheels to use as track tires for an upcoming DE. I went to Tire Rack but cannot seem to locate them in the size of the OEM Cayman S 18' tires. I think I found the fronts but not the rears. Does anyone have a suggestion as to what the closest match would be in terms of size for the rears? Please add link/info in your reply.

Thanks in advance!

brian · #2 (**permalink**) 03-17-2006, 04:31 PM

There is a PCA article about it at http://www.pca.org/tech/tech_qa_ques...3-633A51807E38}

They claim you can use 235x40x18's and 265x35x18's which michelin makes according to this pdf http://www.michelinman.com/assets/pd...otsportcup.pdf

FT · #3 (**permalink**) 03-17-2006, 10:52 PM

As you found out there are no OEM size tire for the cup tires. A compromise set is 245/40 and 275/35. I have been going back and forth on this tire issue and I setteled for those sizes. However, I knew going in that is not the right combination for the Cayman. I wanted to get a feel for myself and determine what the right combination would be, so I chose to go with cheap alternatives for now, so I got Azenis 615s. So far the grip is really good considering they are street tires.

However, after the first track day, I believe that the right size combination is 255/35 for the fronts and 275/40 for the rears. 245/40 and 275/35 combination is not bad, but there is not enough tire in the front and due to the sidewall sections, car is raised 1/8' in the front and lowered 1/8' in the rear, effectively raising the front about 1/4'. I have not corner weighed the car after the tires have been mounted, but I am willing to bet at least 2 additional percent of weight has shifted to the front; which kind of robs from the car's character.

By the way, the Bridgestone RE050 are also proving to be great tires for me, and they have all the right sizes. The proper upgrade sizes are 255/35 and 295/35. Not r-comps, but good tires still [img]/fckeditor/editor/images/smiley/MWPX/regular_smile.gif[/img] There will be more tires coming up within the next 3-4 months, hopefully more brands and size choices.

Also, this thread is a good one on tires I think: http://forums.bimmerforums.com/forum...d.php?t=475535

Cheers,

Edited by - FT on 03/17/2006 5:11:49 PM

**sleepless** · #4 (**permalink**) 03-18-2006, 12:51 AM

I'm using Toyo RA1 in the 245/275 combination on 18' wheels. This setup works quite well.

FT · #5 (**permalink**) 03-19-2006, 05:28 PM

I actually used the stock Bridgestones at VIR, which were really good in terms of durability, comfort and feedback. [/quote]The grip was not great, but darn good for a street tire.<o

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The problem I have with the 245/40 and 275/40 compromise is how the weight balance on the car changes drastically. [/quote]I finally made the calculations: front ride height increased 0.16 in., but the rears decrease by 0.385 in. [/quote]That is significant in terms of weight transfer to the front. [/quote]That is what I do not like about it. [/quote]Otherwise I have little doubt that the Azenis 615 have better grip than the Bridgestones or PS2s for that matter. [/quote]I will find out next week during two-days of autoxing.<o

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The issue for me is that I need tires that are great in the dry and can handle the wet. [/quote]The correct upgrade sizes are 255/35 front and 295/35 rear in order to keep ride height and gearing the same as original. [/quote]Finding a combination that meets all of the above is nearly impossible. [/quote]Only Michelin PS2 and Bridgestone RE050 come in the size, but they are both expensive and if I am going to pay that much money, I'd rather get some r-comps, like the Pilot Cups or Toyo RA-1s.<o

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I have not used the cups, so I cannot give you direct experience; however, many Porsche people use it and like it. [/quote]Bringing them up to temp is the only issue before getting aggressive with them. [/quote]One possible combination 265/35 (only 0.05 drop in rider height for the fronts) and 295/30 sizes (0.68 drop in ride height). [/quote]So, as you can see, it does not look too good either. [/quote]By the way, Michelin has technical guide book on how to use the Pilot Cups and it shows how to open specific threads on the tires to make it suitable in the wet; however, you have to specifically request it and be nice to them [img]/fckeditor/editor/images/smiley/MWPX/confused_smile.gif[/img]
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I used Toyo RA-1s quite a bit and they are great tires. [/quote]The real problem with them is that they love negative camber. [/quote]Depending on the car, they perform at their best between 3.5 and 5.5 negative camber. [/quote]Since our cars lack that capability in stock form, we would chew up the outer edges of RA-1s quite quickly. [/quote]The best part of them, even though they are directional, that is only for wet handling. [/quote]You can flip the tires and get more dry performance on them and they maintain their grip until the belts show off the tires[img]/fckeditor/editor/images/smiley/MWPX/angel_smile.gif[/img] [/quote]They are easy to use, give good feedback and are very predictable. [/quote]I just wish they were making the right sizes, then I really would not mind paying for them.

Another alternative is the Kumho MX tires. They perform very well during autoxing, but I heard that they deteriorate rapidly and incosistenly on the track. I don't have direct experience with them beyond autox.
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So, given all of the above, I went with my non-ideal choice and am waiting for the right size tires to come up. [/quote]One way would be do sent multiple e-mails to Michelin and Toyo directly or through Porsche NA and other manufacturers to come up with the right sizes. [/quote]This does work as it does not require much investment on their part, just demand.


Cheers,

Edited by - FT on 03/19/2006 11:36:29 AM

FT · #6 (**permalink**) 03-23-2006, 02:46 AM

I just came across this thread on Cup tires, FYI:

http://forums.rennlist.com/rennforum...d.php?t=260800

craignyc · #7 (**permalink**) 03-28-2006, 02:16 PM

spencer at F-L told me not to go above 245 on the front, and to use 295 on the rear. Hoosier makes these sizes.

**K-Man S** · #8 (**permalink**) 03-28-2006, 03:05 PM

Craig,

Kip at F-L told me NOT to go as large as 295's on the 18' rears, but according to a tire calculator I found on the web 295 is the largest supported size for the 18' rear wheels.

FT · #9 (**permalink**) 03-29-2006, 01:15 AM

Quote:

spencer at F-L told me not to go above 245 on the front, and to use 295 on the rear. Hoosier makes these sizes.

Interesting. Any particular reason for it, really curious.

willr · #10 (**permalink**) 03-29-2006, 08:13 PM

While it might be nice to experiment with different tyres - particularly R-compound - do you really think the Cayman needs wider tyres? Doesn't it have enough grip for its power already?

**Amazin** · #11 (**permalink**) 03-30-2006, 10:08 PM

You can definitely overtire a car with negative results performance wise.