Thread: 17" vs. 18"
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Old 05-31-2007, 01:25 PM   #4
hamstur
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Join Date: Feb 2007
Location: California
Posts: 16
Here's how to read your tire...

205/50/17 means 205mm width, 50% sidewall aspect ratio, and 17" rim size, so 50% of 205mm = 102mm / 25.4 mm per inch = 4 inch sidewalls.

Your tire will compress about 30% when mounted, so 70% * 4 inchs = 2.8 inches, which means your 2.75 inch measurement is correct.

The OEM front tire for a 996 is 225/40/18, so their height is: 40% of 225 mm = 90mm / 25.4 mm per inch = 3.5 inches * 70% = 2.45 inches.

Porsche does not recommend 19" on 986s and 996s because of the car design...the harsh ride and vibration caused windshields to crack. So...the answer to your question is yes, the sidewalls on the 18" tires will feel stiffer because there is 0.5 inch less sidewall.

If the tires are a bit wide, you would have to shell out a couple hundred for spacers.

Hope this helps,
Andy
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