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Not Yet, I have 2 rear wheels & my name on a center wheel lock kit I know of. The fronts are going to be the issue, they may rub on the shock, my pal has put 991 sports classics on his C4s but he added a spacers.
They look really cool.
I will put a post up when done
By my notes, 997 turbo S centerlocks are 19x8.5 +56 and 19x11 +51, and 991 GT3RS wheels are 20x9.5 +50 and 21x12.5 +48.
That puts the fronts about 1/4" more aggressive (wheel/tire towards the outside of the car) with about 3/4" more wheel towards the shock, and the rears a bit more aggressive (about 3/8") with just over an inch extra clearance needed on the inside.
From how 'sunk' 997 RS Spyder wheels look on my Turbo S, I think the GT3RS wheels would "look/fit" great, assuming there's that extra clearance on the inside.
I'm not sure about the overall diameters though (stock tires go from a 26.2" tall rear tire to a 28.7" rear tire) or the difference in diameters front to rear. Remember none of the GT cars are AWD, so relative tire diameters don't matter for them. Stock Turbos/Turbo S's have ~2% larger rear tires, GT3RS has 5% larger rear tires. Rumored to cause accelerated front diff wear, not sure if that's significant.
Is the AWD system so ultrasensitive to circumference differences that a change of 1-2% is out of spec ? The OEM sizes are off by 2.7%
1. As long as any changes to the front and rear equal - it shouldn't be an issue. E.g. both front and rear tires increase by 1% in circumference. and they maintain the same 2.7% difference from OEM?
Another way to look at it. You somehow (flats/sidewall punctures) end up with brand new fronts that have 12/32 in tread depth and your rears are now at 4/32. These tires would have a 6mm difference or about 1% just on tread depth alone.
Is the AWD system so ultrasensitive to circumference differences that a change of 1-2% is out of spec ? The OEM sizes are off by 2.7%
1. As long as any changes to the front and rear equal - it shouldn't be an issue. E.g. both front and rear tires increase by 1% in circumference. and they maintain the same 2.7% difference from OEM?
Another way to look at it. You somehow (flats/sidewall punctures) end up with brand new fronts that have 12/32 in tread depth and your rears are now at 4/32. These tires would have a 6mm difference or about 1% just on tread depth alone.
I personally wouldn't imagine the front diffs are *that* sensitive, just raising the concern (I did the same math and figured it'd be a larger difference).
If 21" tire choices weren't so limited, I'd have already tried this haha - I want something better than PS4's and don't like Cup2's, and that's about it.
One manufacturers 235/35-19 is not going to have the same physical measurements as 235/35-19 from another manufacturer. You should check the actual measurements. Tire Rack has all that info on their site.
A knowledgable person looked at my earlier post and PM'd this in response - I am going to see if Porsche has a spec.
"Your logic looks correct to me. The car doesn't really work in absolutes when it comes to the AWD system, meaning it won't really care if the rolling circumference is changed by 10% as long as both the front and rear are changed by about the same amount - the speedometer won't be accurate, but you won't damage anything. So it would be possible to mix different diameter wheels as long as the tires mounted on those wheels end up with a similar rolling circumference differential to the stock setup on the car. I'm sure there's some magic number or percentage that shouldn't be exceeded or it results in issues with the differential or transfer case and I don't know what that is, but as you stated, with the stock setup, it's 2.7% so that amount of front to rear difference seems totally fine.
Also mentioned in that thread - you cannot use spacers with centerlock wheels as the CL wheels have little pockets on the back that mate with the locking pins or knubs on the hub to prevent the wheel from rotating independently from the the hub - the CL nut just locks the wheel tight against the hub and on these pins. BTW, these pins or whatever they're called are a wear item with a service life and have a PM schedule I believe, but I don't know what it is off the top of my head."
02-19-2019, 09:30 AM
Will 991 GT3 center lock wheels fit on a 997 TURBO ???
