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Discussion Starter · #1 ·
Hi all,

i searched and did not find the answer to this. i have a 2016 cgts....for the track i have OZ 19 by 10 wheels, i have been using 275-35r -19's for the rear tire, i am wondering if 285-35r-19's will fit without any problem...any help would be appreciated ,thanks in advance
 

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[SoapBox] The negative to going wider at the rear is that the wider tires with no other change will give your car increased understeer unless you make other suspension changes, like wider front tires, softer front sway bar or stiffer rear sway bar or change in alignment. It is all interrelated. [/Off Soapbox]

To answer your question: check your clearance between the tire and the springs and fender liners. If you have 10mm or more space, you are likely good to go. The 10mm extra tread width will be split half on the outside and half on the inside of the rim. You need a minimum of 5mm clearance, so with the current tires, 5mm extra width plus 5mm clearance = 10mm minimum clearance needed vs your existing tires for 285/35-19 to work. If you don't have the clearance, likely a thin spacer will do the trick. The track rod ends should be near the rim lip, so the tire will only run against the fender liner or springs. The only way this might not work is if you have low negative camber in the rear and the spacer pushes the top of the tire too far out of the fender well, where the edge of the fender might come down on the top of the tire.

I am running on my 2014 CS, 295/30-19 on OZ Ultraleggera 11 x 19 inch rims 50mm offset with 7mm spacer (43mm net offset). There is no more room in my rear fender wells without going to 20" rims. I have recently balanced the car with GT3 front swaybar at the softest setting, a Tarett adjustible rear sway bar at the stiffest setting and changing the front tires to 245/35-19.

V6
 

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Discussion Starter · #3 ·
[SoapBox] The negative to going wider at the rear is that the wider tires with no other change will give your car increased understeer unless you make other suspension changes, like wider front tires, softer front sway bar or stiffer rear sway bar or change in alignment. It is all interrelated. [/Off Soapbox]

To answer your question: check your clearance between the tire and the springs and fender liners. If you have 10mm or more space, you are likely good to go. The 10mm extra tread width will be split half on the outside and half on the inside of the rim. You need a minimum of 5mm clearance, so with the current tires, 5mm extra width plus 5mm clearance = 10mm minimum clearance needed vs your existing tires for 285/35-19 to work. If you don't have the clearance, likely a thin spacer will do the trick. The track rod ends should be near the rim lip, so the tire will only run against the fender liner or springs. The only way this might not work is if you have low negative camber in the rear and the spacer pushes the top of the tire too far out of the fender well, where the edge of the fender might come down on the top of the tire.

I am running on my 2014 CS, 295/30-19 on OZ Ultraleggera 11 x 19 inch rims 50mm offset with 7mm spacer (43mm net offset). There is no more room in my rear fender wells without going to 20" rims. I have recently balanced the car with GT3 front swaybar at the softest setting, a Tarett adjustible rear sway bar at the stiffest setting and changing the front tires to 245/35-19.

V6

interesting i am running on OZ 19 by 8.5 in front and using 245 35 19 Bridgestone re 71 in front, in the rear i am using oz 19 by 10 running on 275 35 r 19 bridgestone re 71's

i also just added the tarret bar in rear on halfway setting and the gt3 front sway bar on halfway setting

just got back from putnam was doing alot of vety low 1:21's and the car felt great, will probably stay with above as it all feels balanced and very stable ,thanks for the input, see you at Mid Ohio weekend of 10/16
 

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255/35-19 front and 285/35-19 Cup 2s or RE-71Rs work great on my car. I have OZ Leggera rims of the same size. With GT3 control LCAs in front and eccentric monorail bearings in the rear, the wheels are pushed out 13 mm extra in the front and 6mm more in the rear. I had zero rubbing with the Cup 2s and only an occasional rub with the RE-71Rs on big bumps on the street. With X73 springs and the widening, the car sits another 3-5 mm lower, so the overall ride height is 25 mm lower than stock in the front and 23 mm lower in the rear. It still works with this additional lowering so you should be fine with the 10 mm lowering of PASM. Here is what it looks like. Sorry for repeating this picture, but this topic keeps coming up.
 

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I'm currently on 20" OZ Ultraleggera hlt with 245/35-20, 295/30-20 Kumho PS91 and X73. I have room for an even wider tire in the rear with the 43 offset that these wheels come with. I've done some track sessions and I am looking to get some 19 OZ Leggera as well which come with a bit more aggressive offset. 40 rear and 53 front.

From what I hear and read on the forums the Bridgestone re71 are the wheels to have for AutoX and Track and I know some people are running 255/35-19 and 285/35-19 on cars with X73 without rubbing. I am wondering if the 305/30-19 would fit in the wheel well without rubbing on the 19 Leggera. Has anybody tried this?

I would go 295 but there is no re71r in 295/35 or 30-19 so I'd rather go wider than narrower.

I've seen this 305 tire on 10 rims and while it is pinched slightly it looks ok. I know the Camaro guys are running this setup in the front for AutoX.
 

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No real reason to go with such wide tires. Our cars don't have that much horsepower, and it will upset the inherent balance of the Cayman to have a tire 50 mm wider in the rear. You will get more understeer with tires that big in the rear. A set of 255 and 285 RE-71Rs are as big as will fit on Leggera 19x8.5 and 19x10 rims. Besides the larger tires and wheels to accommodate the 305 tire would weigh a lot more and only slow the car down. My experiences after running 235/265-20 OEMs, 245/275-19s, and 255/285-19s.
 

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No real reason to go with such wide tires. Our cars don't have that much horsepower, and it will upset the inherent balance of the Cayman to have a tire 50 mm wider in the rear. You will get more understeer with tires that big in the rear. A set of 255 and 285 RE-71Rs are as big as will fit on Leggera 19x8.5 and 19x10 rims. Besides the larger tires and wheels to accommodate the 305 tire would weigh a lot more and only slow the car down. My experiences after running 235/265-20 OEMs, 245/275-19s, and 255/285-19s.
Thank you very much for responding. So the general consensus for the stock suspension setup, 255/285 is the best combination for a track setup?

Looking at tire prices there is no much price difference between 19s and 20s, is there a tangible difference downsizing to a 19 wheel? If we're looking at OZ Leggera the difference is a couple lbs per corner at the same tire width.
 

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The 19 inch wheels are lighter as are the tires at probably 3-4 lbs per corner which is a decrease of 12-16 lbs of total unsprung weight. That is huge. Also the 19 inch setup is smaller and will gear the car up by like 3-4%, can't remember exactly off the top of my head. 20s look great for the street, but 19s are better for the track.
 

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The 19 inch wheels are lighter as are the tires at probably 3-4 lbs per corner which is a decrease of 12-16 lbs of total unsprung weight. That is huge. Also the 19 inch setup is smaller and will gear the car up by like 3-4%, can't remember exactly off the top of my head. 20s look great for the street, but 19s are better for the track.
Hi LT - like the HLTs you have. Did you put spacers at all? or no spacers on that set up in your profile pict.
 

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No spacers. The rear has 6mm of additional track via eccentric monoballs on each side plus the extra 10mm built into the offset of the OZ rear wheels, so 16mm + 16mm total in the rear. I would be careful adding a spacer to rear since it would put you at least 15 mm off the original OEM suspension geometry. The front OZ wheels add 4mm of additional track, but the real difference on my car is that with the GT3 LCAs in the front it has 13mm extra track built into the suspension and not just by adding spacers, so front is 17mm + 17mm total additional track width. On a stock car I would add 5mm or 7mm spacers and longer bolts to the front of the car and call it a day. It won't be quite as wide as mine, but will cost much less than with all of the suspension modifications, and it will be balanced with 9mm or 11mm more track on each front wheel with 10mm more track on each back wheel. I have run these OZ Leggera wheels hard at the track, seen the tires slip on the wheels under extreme braking and or cornering, been through numerous of track tires, and not had any problems at all. Highly recommended and affordable wheel upgrade for any Cayman or Boxster.

Here are a few recent photos of the car in action at COTA at this springs Club Race / HPDE. I passed numerous GT4s, GT3s, corvettes, the white and orange race car, and even a GT3 RS. A properly set up and driven mid engined Cayman is a very very capable car.

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