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Cray has a new 2014 line that includes 9.5" wide front wheels and 11" wide rear wheels. These front wheel offsets are 56mm and the rear wheel offsets are 73mm.
They also have wheels with the same widths and offsets as TSW.
This Oz wheel is often in stock at Tire Rack at about $900 each:
The 18 x 9.5 and 19 x 9.5 59mm fronts are listed under the C5 while the 19 x 11 and 20 x 11 75mm rears are listed under the C6. Then a 59mm front wheel with a 3mm spacer is like 56mm.
What's the catch ? It's a little heavy and it's a real three-piece wheel that requires sealing
.
TSW and Cray barrells are different, keep this in mind don't make the mistake I did and buy Cray 18's for the front they won't fit on a Z51.
TSW and Cray barrells are different, keep this in mind don't make the mistake I did and buy Cray 18's for the front they won't fit on a Z51.
We already dealt with that issue once:
Cray 2014 for the Z51:
Front, 19 x 9.5, 56mm, 275/30-19
Rear, 19 x 11, 73mm, 305/30-19
Front, 19 x 9.5, 56mm, 265/35-19 or 275/35-19
Rear, 20 x 11, 73mm, 305/30-20
I don't really like the looks of TSW, Cray, or Forgestar either one. A cast wheel is a risk of a poor alloy mixture. I would probably get the Forgestar F14 in flat black, in the setup that I posted, if that was the budget.
I could do a Superleggera III like this:
Front, 19 x 10.5, 59mm, use 3mm spacer, 295/30-19 Pilot Sport Cup 2
Rear, 20 x 11, 75mm, 305/30-20 Pilot Sport Cup 2
or the 19/19 setup
Front, 19 x 9.5, 59mm, use 3mm spacer, 275/30-19
Rear, 19 x 11, 75mm, 305/30-19
or more front sidewall height
Front, 18 x 9.5, 59mm, use 3mm spacer, 265/35-18 or 275/35-18
Rear, 19 x 11, 75mm, 305/30-19
or the other 19/20 setup with less stagger
Front, 19 x 9.5, 59mm, use 3mm spacer, 265/35-19 or 275/35-19
Rear, 20 x 11, 75mm, 305/30-20
In general, it's a lot of sizes and combinations to keep up with
.
Front, 19 x 9.5, 56mm, 275/30-19
Rear, 19 x 11, 73mm, 305/30-19
Front, 19 x 9.5, 56mm, 265/35-19 or 275/35-19
Rear, 20 x 11, 73mm, 305/30-20
I don't really like the looks of TSW, Cray, or Forgestar either one. A cast wheel is a risk of a poor alloy mixture. I would probably get the Forgestar F14 in flat black, in the setup that I posted, if that was the budget. (Well, I went with flow-formed-cast instead of rotary-cast.)
I could do a Superleggera III like this:
Front, 19 x 10.5, 59mm, use 3mm spacer, 295/30-19 Pilot Sport Cup 2
Rear, 20 x 11, 75mm, 305/30-20 Pilot Sport Cup 2
or the 19/19 setup
Front, 19 x 9.5, 59mm, use 3mm spacer, 275/30-19
Rear, 19 x 11, 75mm, 305/30-19
or more front sidewall height
Front, 18 x 9.5, 59mm, use 3mm spacer, 265/35-18 or 275/35-18
Rear, 19 x 11, 75mm, 305/30-19
or the other 19/20 setup with less stagger
Front, 19 x 9.5, 59mm, use 3mm spacer, 265/35-19 or 275/35-19
Rear, 20 x 11, 75mm, 305/30-20
In general, it's a lot of sizes and combinations to keep up with
.
The original poster is looking for an 18/19 set up that is why I bring it up. I went through the same thing and considered a square 19" set up but good luck finding good track tires for that.
The original poster is looking for an 18/19 set up that is why I bring it up. I went through the same thing and considered a square 19" set up but good luck finding good track tires for that.
Run Z06 spring rates of 531/782 or T1 spring rates of 582/850 and the car will not need a square setup. It will just use its large rear tires and it has a roll-center-height design so that it naturally does that anyway. (I would be looking for 315 rear tires for those spring rates.)
But here are some 19" square or near-square setups:
Oz Superleggera III
Front, 19 x 10.5, 59mm, use 3mm spacer, listed as a C5 rear wheel
Rear, 19 x 11, 75mm, listed under the C6
Front, 19 x 11, 53mm, listed as a C5 Z06 rear wheel
Rear, 19 x 11, 75mm, listed under the C6
Tires are 295/30-19 or 305/30-19. In fact there are R-comps in 315/30-19. The tires are easy to find, you must have meant that the wheels are hard to find.
But 315 tires on the front of a C7 have been the short 315/30-18 at 25.4" diameter. A 315/30-19 is 26.4" diameter. The 295/30-19 is very neat for the C7 front at 26.0" diameter.
Well, if someone says that the Corvette has an off-power push, do they want the front tires the same width as the rear tires or do they want the front tires the same diameter and width as the rear tires ? Because increasing the diameter of the front tires will slow down the turn-in
.
The OEM tires are four sizes difference between front and rear. There's no precisely required tire diameter because the runflats and non-runflats are a little different.
So a four tire size difference with these wider setups would be 265 front with 305 rear. I just avoided a 265/30-19 because of the short sidewall and began at 275/30-19. But it's still a very short front tire sidewall. The 19/20 setups of wide tires have a better front tire sidewall but less selection of tire in the rear tire.
In general, the 19/19 tire setups of wide tires are about 1/2" less tire diameter than OEM non-runflat while the 19/20 tire setups of wide tires are about 1/2" more tire diameter than OEM non-runflat. And then 1/2" in tire diameter is only 1/4" in tire radius.
Tire sidewall height is not included in the tire specs:
Sidewall height = (section-width times aspect-ratio) / 25.4
Also, look at the tire sizes and tire specs very carefully because I didn't pick out 1.5% tire diameter staggers
.
Ok so I found a set of 18 x 8.5 & 18 x 10 for a reasonable price.
Now the question is, when running a 245 F & 285R the difference in tire size is .13" dia. , stock difference is just about an 1", will this make the computer go nuts? Or is it when the tire sizes get to far apart that the computer can't deal with it?
Also you are concerned about sidewall height, what does that affect?
Sidewall height or aspect ratio selection helps achieve the required tire diameter to target the 1" approximate difference between front and rear tires.
As noted, difference in tire diameters for stock tires sizes is about 1". So try to target 1" difference in diameter, but close maybe good enough for the computer.
Tire dia = tire width/25.4 x aspect ratio x 2 + wheel diameter = tire dia
245/40/18 = 245/25.4 x .45 x 2 + 18 = 25.72" dia
285/35/19 = 285/25.4 x .35 x 2 + 19 = 26.85" dia, about 1" diff in diameter
(you can got to the Tire rack website , select "tire specs" and get the tire diameters and rev/mile for comparison.)
So play with available tire widths to fit the rim widths you have and then select aspect ratios to achieve the tire diameters that will give you approximately the 1" diff in diameter between the front and rear tires. Of course, your goal is made difficult because your tire choices are limited to what tires sizes (widths, aspect ratios, diameters) are available in what brands you want.
Ok so I found a set of 18 x 8.5 & 18 x 10 for a reasonable price.
Now the question is, when running a 245 F & 285R the difference in tire size is .13" dia. , stock difference is just about an 1", will this make the computer go nuts? Or is it when the tire sizes get to far apart that the computer can't deal with it?
Also you are concerned about sidewall height, what does that affect?
We all need the full tire sizes to know where you are. It's an 18/18 setup ?
But tire sidewall height is just comfort and protection of wheels. Or if the tire sidewall height goes over 4" then response is being lost.
On the base C7, 245/40-18 front pairs with 285/35-19 rear. On the Z51 C7, 245/35-19 front pairs with 285/30-20 rear. I said four sizes difference between front and rear but that assuming all the other correct parameters. (A 285/35-19 is about the same diameter as a 285/30-20. It's an obvious pattern. But the 285/30-20 has a shorter sidewall height.)
Here is the likely 18/19 wide-tire setup for a C7:
Front, 18 x 9.5, 56mm to 52mm, 265/35-18, 25.3" diameter, 3.65" sidewall height
Rear, 19 x 11, 79mm to 73mm, 305/30-19, 26.2" diameter, 3.6" sidewall height
Now a 265/30-19 will be about the same diameter as a 265/35-18. It's an obvious pattern. But the 265/30-19 will have a shorter sidewall height than the 265/35-18.
So the likely 19/19 wide-tire setup:
Front, 19 x 9.5, 56mm to 52mm, 275/30-19, 25.5" diameter, 3.25" sidewall height
Rear, 19 x 11, 79mm to 73mm, 305/30-19, 26.2" diameter, 3.6" sidewall height
.
We all need the full tire sizes to know where you are. It's an 18/18 setup ?
But tire sidewall height is just comfort and protection of wheels. Or if the tire sidewall height goes over 4" then response is being lost.
On the base C7, 245/40-18 front pairs with 285/35-19 rear. On the Z51 C7, 245/35-19 front pairs with 285/30-20 rear. I said four sizes difference between front and rear but that assuming all the other correct parameters. (A 285/35-19 is about the same diameter as a 285/30-20. It's an obvious pattern. But the 285/30-20 has a shorter sidewall height.)
Here is the likely 18/19 wide-tire setup for a C7:
Front, 18 x 9.5, 56mm to 52mm, 265/35-18, 25.3" diameter, 3.65" sidewall height
Rear, 19 x 11, 79mm to 73mm, 305/30-19, 26.2" diameter, 3.6" sidewall height
Now a 265/30-19 will be about the same diameter as a 265/35-18. It's an obvious pattern. But the 265/30-19 will have a shorter sidewall height than the 265/35-18.
So the likely 19/19 wide-tire setup:
Front, 19 x 9.5, 56mm to 52mm, 275/30-19, 25.5" diameter, 3.25" sidewall height
Rear, 19 x 11, 79mm to 73mm, 305/30-19, 26.2" diameter, 3.6" sidewall height
.
I was looking for an 18/19 setup I could run the stock tire sizes on to get to know the car, then after a while could run hoosiers or kumho's in the larger widths. But I haven't been able to find that without spending 5k.
I found some OZ wheels @ tire rack for the C7 Z51 but they are both 18's for under 2k. In the street tire class I want to run hankook rs3 or dunlop direzza star spec. These seem to be the best street tires available.
But the stock sizes are 285/30/18 R & 245/40/18 F, they are pretty close to the same size. So I don't know if the computer wants the F to R ratio close to 1" or can it be even with out upsetting it?
If this doesn't work I'll probably buy a set of stock style knock offs to mount street tires on and just autocross them. Do you have an opinion on the "generic" stock style wheels?
Wow, well, SCCA Street class autocross with a C7 Z51 requires front/rear wheel diameters of 18/19, 19/19, 18/20, or 19/20. Then the wheel widths must be 8.5" front and 10" rear. Finally, the front wheel offsets must be 56mm to 49mm and the rear wheel offsets must be 79mm to 72mm.
Also, the tire must be 200 treadwear or greater. So I searched 295/30-20, 285/30-20, 295/35-19, and 285/35-19 for 200-treadwear autocross tires. I found the Rival (including old stock) in 285/35-19 and the RE-11A in 285/35-19. Those are rear tires of course.
The RS3 is available in the tall 285/35-20 rear tire. The front tire would be the tall 245/40-19.
I wouldn't worry about the difference in front and rear tire diameters. It is often run at 0". I would run it between 0.5" and 1.25" difference with the front tire shorter than the rear tire. Just check the tire specs carefully
.
Wow, well, SCCA Street class autocross with a C7 Z51 requires front/rear wheel diameters of 18/19, 19/19, 18/20, or 19/20. Then the wheel widths must be 8.5" front and 10" rear. Finally, the front wheel offsets must be 56mm to 49mm and the rear wheel offsets must be 79mm to 72mm.
Also, the tire must be 200 treadwear or greater. So I searched 295/30-20, 285/30-20, 295/35-19, and 285/35-19 for 200-treadwear autocross tires. I found the Rival (including old stock) in 285/35-19 and the RE-11A in 285/35-19. Those are rear tires of course.
The RS3 is available in the tall 285/35-20 rear tire. The front tire would be the tall 245/40-19.
I wouldn't worry about the difference in front and rear tire diameters. It is often run at 0". I would run it between 0.5" and 1.25" difference with the front tire shorter than the rear tire. Just check the tire specs carefully
.
I was under the impression you could go up or down a wheel size and stay in the stock class. So you have to change both wheels if you change? You can't change just the rears for an 18/18 setup?
Another question, when you move into SSR race tire class do the wheels have to be stock width also?
I have spent many hours trying to find wheels to fit in the 18/19 setup.
It appears to stay in the stock wheels sizes you have to go with very expensive forged, or buy a set of stock "aftermarket" wheels. One of the vendors on this forum tells me he has a set i 18/19 stock style that will clear the z51 caliper.
In your opinion are these cast wheels strong enough to autocross a 3300 lb car without having problems?
I hate to go on and on about this but i'm struggling to come up with a wheel set that will work without spending 5k.
In Street class autocross, the wheel diameters can be changed by up to 1". And the wheel offsets can be changed by up to 7mm but including the use of wheel spacers.
Then the C7 Z51 comes stock with 19/20 wheels.
I can find a set of 18/19 or 19/19 Oz Superleggera III at about $900 each that meet the rules and those are listed under the C6. They are not lighter than OEM wheels but very custom looking. Forgestar has a 19 x 8.5 55mm front and a 19 x 10 75mm rear in the F14F. Find the sizes on the Forgestar website and price the wheels on the Howey Industries website. There's an incredible Oz Superforgiata 19/20 set at TR that meets the rules but those are about $1500 each.
Other autocross classes ?
SSR requires both OEM diameter and width wheels but uses R-comp tires
STU limits tires at 285
SSP doesn't limit wheels or tires but posters are saying that coilovers are not allowed. However, the car should have a suspension. Also, flared fenders are allowed.
SSM doesn't limit wheels or tires but coilovers are allowed. Flared fenders are allowed
.
In Street class autocross, the wheel diameters can be changed by up to 1". And the wheel offsets can be changed by up to 7mm but including the use of wheel spacers.
Then the C7 Z51 comes stock with 19/20 wheels.
I can find a set of 18/19 or 19/19 Oz Superleggera III at about $900 each that meet the rules and those are listed under the C6. They are not lighter than OEM wheels but very custom looking. Forgestar has a 19 x 8.5 55mm front and a 19 x 10 75mm rear in the F14F. Find the sizes on the Forgestar website and price the wheels on the Howey Industries website. There's an incredible Oz Superforgiata 19/20 set at TR that meets the rules but those are about $1500 each.
Other autocross classes ? STU requires a 285 tire and so that's very restricted for a Corvette. A car in STU should have a suspension. There are two STU builds on the Autocross forum. I guess the other class is SSM ? Wheels and tires are likely unrestricted and fender flares are probably allowed. A car in SSM should have a suspension. Gosh, there's nothing in between a class of restricted tire sizes and and a class of fender flares allowed
.
My thinking on the 18/18 setup is the z51 is an add on package to the base car, therefore you could use the base 18/19 wheels to change one wheel size to an 18/18 setup.
My thinking on the 18/18 setup is the z51 is an add on package to the base car, therefore you could use the base 18/19 wheels to change one wheel size to an 18/18 setup.
I don't know about the rules but your rear tire has a sidewall height that is too tall
St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13
Originally Posted by leadville1
Word of caution Cray's don't fit the Z51 Caliper in the 18" size the barrel is too small. You need to use TSW, the Interlagos is a great looking wheel by the way.
I tried to fit the 18" Cray's on my Z51. Nice that Les Schwab took them back and replaced them with 19s. Probably smart that I asked the Schwab guy if 18s fit before I ordered them.
Well after much research, I found the only wheels that will fit a C7 Z51
(without spending 5K) are the GT-2 wheels from LG racing or corvette mods. So I ordered a set and they fit perfect. Auto crossed with them last weekend and was happy. They are a 1/2" wider than stock which technically will put you out of the stock class, but I run the stock size tires. It just depends how picky your local club is.
I can't really figure out who writes these rules when a C7 can't run wider tires but has to compete with a C7 Z06.
I also see they dropped the C6 Z06 down to A Stock from Super Stock. Whats up with that? Seems the C7 and C6 Z06 would be pretty close competition.
Well after much research, I found the only wheels that will fit a C7 Z51
(without spending 5K) are the GT-2 wheels from LG racing or corvette mods. So I ordered a set and they fit perfect. Auto crossed with them last weekend and was happy. They are a 1/2" wider than stock which technically will put you out of the stock class, but I run the stock size tires. It just depends how picky your local club is.
I can't really figure out who writes these rules when a C7 can't run wider tires but has to compete with a C7 Z06.
I also see they dropped the C6 Z06 down to A Stock from Super Stock. Whats up with that? Seems the C7 and C6 Z06 would be pretty close competition.
Nobody will care about your rims unless you start winning.
I will be using the OEM rims on my Z51 with hankook RS3s, 245s and 305s hopefully they won't rub on the rear.
I wouldn't be surprised if the C7Z51 is very competitive with the C7Z06 and that it will come down to the course, not unlike the C5Z06 vs the C6Z06 where the C5Z06 was usually the better car on tighter courses because it was lighter, better geared, and skinnier.
Cray, Beyern, etc... are all TSW. some are Hub-centric.. some not.
I love my Interlagos on my Twin Turbo Flex. Want a set for my Z51, but Wiffee... says Noooo.*.., even though I would be willing to sell my Black stock wheels.
Life can SUCK!
* I have like 2 - 3 sets of custom wheels for all my (4) cars. So, some way.... some how I will WIN! Plan.. Black Interlagos... and get rid of stock black wheels. THEN... a year or 2 later, some fancy custom wheels in silver... polished, machine, painted, whatever... Just have to look Kick A....
02-22-2015, 10:03 AM
I tried to fit the 18" Cray's on my Z51. Nice that Les Schwab took them back and replaced them with 19s. Probably smart that I asked the Schwab guy if 18s fit before I ordered them.
