12
Oct

Hi - I am looking to buy these porsche 993 Cup wheels for my 1988 951. The wheel dimensions are as follows (wheels are OEM, not replica) Dimensions for Back wheels : 17 x 9 with Pirelli P6000 255/40/ZR17. Front wheels : 17 x 7 Michelin Pilot SX 225/45/R17

I am pretty sure that these wheels will fit my 951 given the later year offset, but I was wondering if this dimension of tires affects the handling and performance of the automobile? in a negative way?

Thanks!


Answer:
As far as fit, if there is a problem it will be with the offset… a 951 should be able to sit 17×7s and 17×9s without any issue.

As far as performance, when looking at wheels/tires there are three areas that come into play: contact area, gearing, and weight.

Contact area is mostly simple, more is better! With taller and wider wheels, you’re getting more contact, and thus more grip. The only possible negitive here (depending on tires used and specifics of suspension setup) is that adding too much width in the front will begin to limit the slip angle where your tires will be effective. Though the tire widths you'd fit at 7″ are not likely to run into problems.

Gearing: while taller is superior for the contact patch of the tire, it will increase the overall gearing, which can have a negitive impact on performance. Though if your tire sizes are basically the same, this won't matter (though it will also negate the increase in grip you get from having taller wheel/tire combo).

Weight: this can be a killer as we are dealing with unsprung rotating mass. Depending on what you are taking off, the 993 Cups are most likely a couple pounds heavier each (and the corresponding tires are likely a pound or two heavier than their 15 or 16″ counterparts). Ultimately, you might feel a little difference in acceleration (potentially even braking, but probably not for this small change)… but likely not too much (the more power you have the less noticeable this will be).

The other negitive here’s with the tires… mismatched tires are never a good idea from a performance standpoint (though this is easy enough to correct).

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This entry was posted on Sunday, October 12th, 2008 at 6:11 am and is filed under Porsche. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or TrackBack URI from your own site.

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