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18" vs 19" track wheels - 997 GT3

 
Old 06-21-2007, 09:51 AM
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ngoldrich
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Default 18" vs 19" track wheels - 997 GT3

I see the cost is slightly higher for the 19" - any other reason not to go with 19" instead of 18" for an extra set with 'R' compound tires?

Thanks,
Norm
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Old 06-21-2007, 10:00 AM
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TripleM
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1. Easier to find 18in tires, more choices.
2. 18in has lower rotational mass, so better for track.
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Old 06-21-2007, 10:03 AM
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TripleM thanks for the info...

Do you have to lower the car when running the 18"s to get optimal handling or is the overall dia the same with a taller sidewall?

Norm
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Old 06-21-2007, 11:14 AM
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TripleM
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I m awaiting my GT3 in Dec so currently I m speaking from my own experience in my BMW M3 where I run 19in on street and 18 on track.
The car is already lowered so when I put on 18, the taller sidewall by 5mm front and back pretty much sorts out the dia issue.

It's definitely alot more satisfying going with 18in on track
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Old 06-21-2007, 11:48 AM
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18 also has smaller OD so maybe better gearing for you. Depends on the track though
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Old 06-21-2007, 12:01 PM
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Any issues with clearance with 18" and PCCB?
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Old 06-21-2007, 12:25 PM
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Ray G
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I know that the 997 Cup cars run 18" wheels. Don't know about PCCB clearance tho.
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Old 06-21-2007, 02:11 PM
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I was using OEM 19s on my 997s until my 18s came in recently. I matched my 18" Fikse Profil 13s with Toyo RA1s, which have the exact same OD as the oem 19" set that came on the car. Width is greater on the 18s at 245/305. I posted my first impressions elsewhere at RL, but here's a portion that I thought long and hard about to answer a question on my thoughts on performance.

Five things have happened by changing the tires and wheels: 1) I dropped about 5 lbs per corner in weight from lighter wheels, which will add to performance in acceleration and braking, 2) I increased grip by going from summer to R-compound, 3) I increased my contact patch by going wider to 245/305, and 4) I probably will have a higher quality contact patch on rough track due to the more compliant design (18", side wall flex), and 5) All of this adds up to increased G forces on cornering, braking, and acceleration.
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Old 06-21-2007, 03:54 PM
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Having run 19's on the previous 997 GT3, I've gone wih steel brakes and 18's on the current one. Overall less weight, more resilient over berms (shattering or at least damaging a 19 is always in the cards at the track.) Some 18's will clear front PCCB rotors but not the factory wheels and not the RG5 Champions or the 996 GT3 wheels. I believe there's a BBS 18" design that clears PCCBs. As mentioned here and in other threads on the topic, there are some more appealing tire options and sizes for 18's. The overall difference in revolutions per mile is trivial and the "look" of the car with the correct ride height (minimum spec) is good without looking silly or slammed.
The track makes wheels a "consumable" so keeping the factory 19's for the street means they look nice and the tires last a bit.
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Old 06-21-2007, 07:05 PM
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but doesn't the thicker sidewall of 18" tyres change the handling? Don't you need to adjust the suspension to match?
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Old 06-21-2007, 09:57 PM
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No.
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Old 06-22-2007, 02:52 AM
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Originally Posted by willr
but doesn't the thicker sidewall of 18" tyres change the handling? Don't you need to adjust the suspension to match?
You're quite right, but in this case for example, it's probably insignificant.

The spring, damper and roll bars should be matched to the grip of the tire and its other characteristics, especially sidewall compliance. But in the grand scheme of things, the changes are not simple. In technical terms, from unsprung weight to bushing design to the flex in the control arm itself, it's all one big mish-mash. : )

F'rinstance, you can imagine the tire manufacturer has tried to compensate for the lower profile of the 19 (with about the same revolutions per mile) to make it similar to the 18, especially for a mostly street-oriented tire application. So I would expect -- and my humble but-o-meter readings bear this out -- the 19's are not a significant change from the 18's in terms of suspension tune compensating for the reduction in sidewall. If there's any difference, I notice some extra movement side to side in the rear and maybe a little more wriggle and wander in the front. But the 19's do look great! : )
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Old 06-22-2007, 04:21 AM
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Originally Posted by jhbrennan
Any issues with clearance with 18" and PCCB?
I had some issues, but Fikse is working on it now and will correct the issue in time for my RS in August.
I am going with the Fikse Prfil 5S. I ordered them from CDOC. After finding the clearance to be a problem, Fikse has been very good about getting it figured out. I am dealing directly with Will at Fikse on the issue. And Jim Fikse is working on it as well.
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