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Hi All

I know Christmas is upon us, but I must admit that my mind is drifting toward spring when I plan to take my newly acquired 981 CS to some DE & AutoX events. I have participated in AutoX in the past but always kept things stock.

My initial plan form the Cayman is to keep things stock. My Cayman came equipped with the 20 inch Carrera wheels. I am thinking about obtaining a dedicated set of wheel/tires for track use. I have scanned the forum for previous discussions on this subject. I saw a lot about 18 v 19...and 19 v 20, although the latter focused primarily on ride comfort/looks.

What about performance differences among the three sizes? I saw a thread on the Rennlist on this very topic, but it was over 5 years old and 987 based. Will 18 inch wheels even fit? I assume the 981 was engineered around a 19 inch wheel. So, what are the pros/cons to moving up to a 20 inch or down to an 18 inch for track use?

Oh...a very Happy Holiday season to all.
 

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Hi VaCat33,
I am also considering the same and have been leaning toward 19 inch tires and wheels, mainly because cost and a available options for both wheels and tires are better on 19 inch than 20 inch. I have PCCB so 18 inch is not an option for me.

Curious on how this discussion goes!
 

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I'm aware of several 981 S using 18" wheels at the track. Availability as well as tire selection play a role here. Not only that, but WHEN you go off (NOT IF) you have a little extra sidewall to prevent wheel scratches; but that is not saying much since it depends on where on the track it happens..
 

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Are you certain that 18's won't fit?

Hi VaCat33,
I am also considering the same and have been leaning toward 19 inch tires and wheels, mainly because cost and a available options for both wheels and tires are better on 19 inch than 20 inch. I have PCCB so 18 inch is not an option for me.

Curious on how this discussion goes!
 

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I had assumed the 18 inch wheels would not fit under PCCB since the Porsche Configurator in the past would not allow you to configure a Boxster or Cayman with PCCB and 18 inch wheels. However, I just checked the new configurator and it does allow it. Looks like I need to do some more checking as my memory may be off.

Thanks for bringing this up!
 

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Tire selection was a big determining factor for me. I was looking to run Dunlop ZII (in SCCA Street category autocross) and they only went up to 19". I'd have a bigger selection of sizes if I went down to 18", but I wasn't sure if they'd fit over the PCCB either. (I'd be interested to hear of any one with an S and PCCB if they fit.) The SCCA rules also allowed for wider wheels in 19" than 18", wider is reckoned to be an advantage.

A lot depends on who's rules you want to run under.

In general smaller wheels are lighter, which is better. Larger wheels may allow you to run lower profile tires, which is an advantage. The larger wheels also tend to be wider, another advantage. There was one magazine which tried to test this and came to the conclusion that (at least in the case they tested) the wheels 1" down from the largest provided the best performance. The Cayman's gearing is very tall, so you might get some advantage if you can run a smaller diameter wheel with a lower profile tire (for smaller overall diameter). With PDK gear changes are almost "free", so lower gearing should be an advantage.
 

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Here are 18" 987.1 BS wheels on a 981BS


These work with 245-275/40-18 tires--NT01 right now, which I highly recommend.

Too echo what Amdeutsch said, Someone told me years ago when I started doing DEs that more side wall is better when you go off and from what I've seen they were spot on.
 

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From all I read and all things equal, larger wheels/RIMs and lower profile tires increase track times. More wheel spin will happen and the car will be less controlled, nonetheless, handles sharper and faster. Any tire sidewall will flex enough to maintain grip, but some do it too much. More tire usually means the car starts veering off from where you want it and there is a feeling of more 'play' in the steering that will be obvious at higher speeds. Kind of depends on the tire too...high performance larger tires have a stiff sidewall almost to imitate larger wheels. More metal/ harder tires means the wheels are ruthless and tolerate less. I hear some actually prefer the more natural 'easier' control feel of more tire and less metal.

Tests have shown that lighter wheels are always faster in a straight line. Larger wheel means its heavier, but not always.

IMO, tire choice and pressure is going to make more of a difference than 1 inch (+/- 19). If you think you can get better tires for 18 inch wheels, they'll work better. Race cars will actually have larger tires and smaller wheels, but that is because they use crazy expensive/ unique tires that are for track only and wear out like paper.

Most people have 20 inch wheels and there's a reason they are standard on GTS and 911 models. Good looks and practical handing for the streets and track.
 
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