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Old 11-16-2010, 06:06 PM   #1
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17 vs 18" tires for autocross/DE

Hello

I am considering buying a second set of wheels and tires for autocross and DE events. My DD wheels are 18". In order to make this more affordable, i thought about getting 17" wheels and tires.

My question is: is there a considerable loss in handling when going to a smaller diameter ?

Thanks
Leo
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Old 11-16-2010, 06:21 PM   #2
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A lot of folks go to 17,s because the price and selection of tire are much broader,you may very well get much better traction with 17,s which means you should look into engine oiling mods
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Old 11-16-2010, 07:05 PM   #3
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The difference in traction will be negligible, if any.
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Old 11-16-2010, 08:24 PM   #4
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Quote:
Originally Posted by Pat
The difference in traction will be negligible, if any.
Yes, but you will get quicker acceleration with the 17's, and lighter weight should mean shorter braking too...
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Old 11-16-2010, 08:54 PM   #5
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No handling difference. 17s are faster and a lot less $$ for tires. 18s look better for your street tires IMHO.
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Old 11-17-2010, 09:23 AM   #6
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Thanks to all. Indeed, the intent is to have a 2nd set of tires/wheels for track/AX days. It will be definitely a lot cheaper to go with the 17", and apparently there is not a whole lot to lose in terms of performance.

thanks again !
Leo
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Old 11-19-2010, 10:32 AM   #7
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I have to disagree with this group.... 18s are faster - maybe 1/2 second (AX reference). Better response.... and not necessarily heavier (combo of wheels and tires), depending on what you buy.

However, the economics mentioned are a real concern.... several hundreds more for tires.

Just reread your question.... smaller (tire) diameters will likely help your gearing in AX and may require gear changes at inopportune times at the track (depends on the track).

good luck,

kj

Last edited by Boxster44; 11-19-2010 at 10:44 AM. Reason: add'l
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Old 11-19-2010, 03:48 PM   #8
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my 2 cents

tire heights for 17 and 18 (overall diameter including tire)
should be negligible unless you stray from recommended
Porsche sizes for each respective rim diameter
If there is a difference..then the tire that is smaller in diameter
should give an advantage at the start of a race.

lower profile tire equals less squirming when cornering
therefore more precise steering, less sidewall flex, less heat generated

taller profile tire equals more flex in sidewall ...which generates heat
but less precise steering

16's are good for a plush ride...probably the best for winter driving
17's are good at filtering out most road imperfections
18's let you know of every imperfection in the road
19's make you feel every imperfection in the road

my 4 cents
Cheers
Chris
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Old 11-20-2010, 06:13 AM   #9
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If you're getting R-comps the only thing that matters is cost of tire. And cost of tire is cheaper for 17"s. Put the 8.5" rears all around with wider front tires and you should be set.
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Old 11-21-2010, 08:23 AM   #10
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Thanks

Will probably get a second set for next season.

Leo
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