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18 inbch wheels on 964?

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Old 03-03-2011, 11:32 PM
  #16  
ACSGP
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Originally Posted by NinetyOneC2
Bah! I'm not worried at all. I can imagine that if you're going 150 mph into a bend that the forces transferred by an 18-inch wheel and tire combo are great than 16 or 17 but at North American speeds...hardly an issue. Now if you track you car...
Yes, but if you use lighter 18" forged rims, there's less mass, and therefore less force. The 17" Cup 1s weigh a ton.
Old 03-04-2011, 12:59 AM
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LastMezger
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Originally Posted by ACSGP
Yes, but if you use lighter 18" forged rims, there's less mass, and therefore less force. The 17" Cup 1s weigh a ton.
Excellent point. Hadn't considered that.

Part of the issue, however, is that the shorter sidewalls transmit more impact to the suspension components. A car's tire sidewall flex is an integral part of the suspension "tuning".
Old 03-04-2011, 10:14 AM
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Originally Posted by altarchsa
"..........only reason I changed wheels was those dreadful "style" 90 Phone dial wheels............."

Heyyyyyy... (see the avatar) You can see I have no experience with this, but you might want to at least look at:

http://www.pcarworkshop.com/images/d...0593geolab.pdf

This PCNA Technical Bulletin says "Retrofitting 18" wheels on Porsche vehicles which do not have 18" wheels as original equipment is NOT ALLOWED." While this was a technical issue back in 1993, everyone with 18" wheels here yells BS every time it's brought up. You might want to consider following the guidelines for upgrading to 17" wheels by fitting the improved caster mounts.

Now, everyone can restate, "Don't worry, it'll be fine...........
Saw that and would just check on the fittings more offten if running 18s. That said we run 17s on both our 964s. Mostly because I like the look of Cup IIs on a 964. Plenty of choices for 17” tyres from Toyo, Nitto, Hoosier, Michelin and others.
BTW Tech Bulletins are seldom BS! Looks like what it says is that Porsche wants their customers to be aware of a possible situation so they can make an informed decision. IIRC there’s another one about running 18s on early 993s. I think that one recommends reinforcing certain areas of the chassis.



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