<table width="500" height="74" cellspacing="1" cellpadding="1" border="1" align="" summary="">
<tbody>
<tr>
<td>Michelin Pilot Sport</td>
<td>Front</td>
<td>%</td>
<td></td>
<td>Rear</td>
<td>%</td>
</tr>
<tr>
<td>size</td>
<td>235/40/18</td>
<td></td>
<td></td>
<td>265/40/18</td>
<td></td>
</tr>
<tr>
<td>diameter (mm)

</td>
<td>645</td>
<td></td>
<td></td>
<td>668</td>
<td></td>
</tr>
<tr>
<td>rear diamater as % of front</td>
<td>103.6%</td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>Dunlop D02</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>size</td>
<td>235/40/18</td>
<td></td>
<td> </td>
<td>265/35/18</td>
<td></td>
</tr>
<tr>
<td>diameter (mm)</td>
<td>644</td>
<td>99.8%</td>
<td></td>
<td>643</td>
<td>96.3%</td>
</tr>
<tr>
<td>rear diamater as % of front</td>
<td>99.8%</td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>Michelin Sport Cup</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>size</td>
<td>235/40/R18</td>
<td></td>
<td></td>
<td>265/35/R18</td>
<td></td>
</tr>
<tr>
<td>diameter (mm)</td>
<td>645</td>
<td>100%</td>
<td></td>
<td>640</td>
<td>95.8%</td>
</tr>
<tr>
<td>rear diamater as % of front</td>
<td>99.2%</td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>Pirelli P Zero Corsa</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>size</td>
<td>235/40/R18</td>
<td></td>
<td></td>
<td>265/35/R18</td>
<td></td>
</tr>
<tr>
<td>diameter (mm)</td>
<td>635</td>
<td>98.4%</td>
<td></td>
<td>635</td>
<td>95.1%</td>
</tr>
<tr>
<td>rear diamater as % of front</td>
<td>99.9%

</td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>Toyo</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>size</td>
<td>235/40/R18</td>
<td></td>
<td></td>
<td>265/35/R18</td>
<td></td>
</tr>
<tr>
<td>diameter (mm)</td>
<td>648</td>
<td>100%</td>
<td></td>
<td>646</td>
<td>96.7%</td>
</tr>
<tr>
<td>rear diamater as % of front</td>
<td>99.7%</td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>Yokohama Advan</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
<tr>
<td>size</td>
<td>235/40/R18</td>
<td></td>
<td></td>
<td>265/35/R18</td>
<td></td>
</tr>
<tr>
<td>diameter (mm)</td>
<td>645</td>
<td>100%</td>
<td></td>
<td>640</td>
<td>95.8%</td>
</tr>
<tr>
<td>rear diamater as % of front</td>
<td>99.2%</td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
</tbody>
</table>


I have been looking further into track tyres, and speaking to Porsche Motorsport technician. It appears that the Cayman S (and Boxster) both have a standard rear tyre which is a larger diamater than the front. This is unusual. There are no tyre manufacturers that make a track tyre in the right profile.



All available track tyres have a smaller diameter in the rear. The difference is between 3% and 5% of the OEM tyre. This will affect speedo, gearing, space on wheel arches and possibly ABS and PSM.



Apaprently the smaller diamater of available track tyres is a GOOD this on the track. More punch out of corners, less tyre roll.



According to people on this forum, no one has reported issues with ABS and PSM. So on this experience, I am going ahead and fitting the Dunlop tyres. I chose Dunlop because the advice I have is that the Dunlop have good dry performance (although not as good as Michelin) but VERY good wet performance. They are the prefered choice in Oz of some of the leading Porsche drivers in tarmac rallies.



I am also getting a suspension alignment as well.



I am doing a track day next week, so I will report on differences in lap times against the OEM tyres (providing track conditions are similar)



I thought all of this may be of use for others...



Apparently the ideal scenario would be to maintain the OEM ratio between front and rear diameter. This means using the same profile on front and rear. Unfortunately no one makes a 235 track tyre in 35 profile, so using a smaller front is not an option.



If tyre manufacturers out there are listening, please make us some Cayman specific track tyres to fill those wheel arches!

i dont think toyo comes in the size you specified. they should be 245/40/18 and 275/35/18. this is what i run, zero prob whatsoever. toyo is very grippy dry and wet. last quite some time and can be drivein on street no problem. you can even flip them on the rim to even out wear if you have seiours camber.

__________________
if you want the best for your toy, look no further:

http://www.premiermobilegroup.com/ (one of the best clear film specialists)
http://www.sharkwerks.com/main.php (bring your money, alex will help you spend it in a GOOD way)

btw, check nitto nt01. they are prettymuch the same as Toyo RA1. i use them interchangeable depending on which is lower priced at the moment.

__________________
if you want the best for your toy, look no further:

http://www.premiermobilegroup.com/ (one of the best clear film specialists)
http://www.sharkwerks.com/main.php (bring your money, alex will help you spend it in a GOOD way)

The Toyo tyre on the chart is the Toyo Proxes R888, not Proxes RA1

Glad to hear you have had no problems. I'd hate to confuse my ABS and PSM on the track.

I suppose with the rears being a smaller diameter than standard, the rears will be rotating faster than normal. I think this means that the ABS on the front tyres might kick in a microsecond sooner if the fronts lockup, or a microsecond later if the rears lock up?

Edited by - dt on 06/28/2006 11:22:46 PM

I just dropped my car off to have the tyres fitted, and put the new race tyres up against the Pilot Sports. There is a HUGE difference in the diamater of the tyre. Its going to look quite different on the car. I really hope there are not handling issues as a result, as I love the way the Cayman handles in its stock form. From all reports from those already with track tyres there are no issues. So hopefully I don't experience any either.

I just found this link in a previous thread which talks about this same issue. It seems that it has been covered previously.

http://www.pca.org/tech/tech_qa_ques...3-633A51807E38