Will 20" Wheels X 10" fit on a 99' Formula and if what tires

**FormulaBird** · 06-17-2013, 08:11 AM

Hey, I'm the process of getting new wheels, tires, rotors, calipers, pads, lines for a 99' M6 Formula LS1 and having a hard time matching all the sizes to work together safely.

Currently, the wheels I like are 20" X 10" width 5X120.65 (+40 offset, 65mm Hub); I am 1) curious whether I can fit those 4way all around and what our hub measurement is? I know the 10s can fit on the rear no problem given that a lot of people are running 11s but will they fit the front okay?

2) if I can fit 10s all around then can I fit 305 tires on the back and 285 on the front or will I have rubbing issues? Will I need to down the front to 275 or down the back to 295 or bring them both lower? Also, what will the aspect ratio be on a 275 or 285 20" wheel and on the rear 305 or 295 be, so rear 305/??/20" front 285/??/20".

Finally, given the wheels and tires that will hopefully work okay and given the offset of +40 above, 4) can I install the CTS-V or C5 brake calipers without hitting the rim with some Brembo slotted rotors and if so 5) what is the largest rotor size(besides the big brake kits $$) that will work with these calipers?

Any help is much appreciated guys, I figured this is the one place where I maybe able to get some quality answers. Thanks.

**98TransAmWs-6** · 06-18-2013, 09:04 AM

Originally Posted by FormulaBird

Hey, I'm the process of getting new wheels, tires, rotors, calipers, pads, lines for a 99' M6 Formula LS1 and having a hard time matching all the sizes to work together safely.

Currently, the wheels I like are 20" X 10" width 5X120.65 (+40 offset, 65mm Hub); I am 1) curious whether I can fit those 4way all around and what our hub measurement is? I know the 10s can fit on the rear no problem given that a lot of people are running 11s but will they fit the front okay?

2) if I can fit 10s all around then can I fit 305 tires on the back and 285 on the front or will I have rubbing issues? Will I need to down the front to 275 or down the back to 295 or bring them both lower? Also, what will the aspect ratio be on a 275 or 285 20" wheel and on the rear 305 or 295 be, so rear 305/??/20" front 285/??/20".

Finally, given the wheels and tires that will hopefully work okay and given the offset of +40 above, 4) can I install the CTS-V or C5 brake calipers without hitting the rim with some Brembo slotted rotors and if so 5) what is the largest rotor size(besides the big brake kits $$) that will work with these calipers?

Any help is much appreciated guys, I figured this is the one place where I maybe able to get some quality answers. Thanks.

I have 20x8 and 20x10 boss 338 wheels on my TA with. I put the rears on the front at one point for checking fitment at one point and they fit just fine. I fit 295s no problem in the rear but I have not tried 305s. I have done the cts-v brake swap with 14" z06 rotors but whether your wheels will hit is dependant on if the spoke are concave or convex. I had to run a spacer still but my spokes are concave. Also our hub bore is 70.3 so you will have to bore out the 65mm bore to 70.3. That is what I did as I had a similar issue and it was easy. Here are some photos:
Hub bored out

Spacer

**FormulaBird** · 06-18-2013, 09:42 AM

Thank you so much, that cleared up a lot and those look pretty nice. Now I can go a head and get the 20 X 10 on all 4. They also come with the bore option of 67 or 72.6mm so I'll just go with the 72.6mm with +40 offset since you said we're 70.3 and hopefully can track down some Foose rings to make it fit rather than widening the hole. I'll dress them in 275/25 and 295/25 with 14" and 13.4" slotted stop tech rotors and the zo6 calipers (I know, complete turnaround from what I initially intended

). Can't wait to see the end result given that this is costing a small fortune.

**98TransAmWs-6** · 06-18-2013, 09:49 AM

C6 z06 calipers aren't direct bolt on like the cts vs are btw, you have to drill the spindle. I did 30 series tires for me and they didn't rub. If you plan on racing at all I would look at that.

**FormulaBird** · 06-18-2013, 11:14 AM

I didn't know that, I thought they bolted the same. I guess I'll have to mod the spindle.

Interesting that 30 tires worked w/o rubbing, I was going 25 cause I figured the overall wheel diameter would have been 25.41 on the front 275/25/20 and 25.81 on the rear 295/25/20 since I believe our stock diameter is 25.66 so I didn't want to go way off. At 30 the front will be 26.49 and rear 26.96 so a bit off but I guess if it works then I'd rather do 30 for a better ride, thanks!

Do you happen by to know by any chance if I'll need this C6 conversion brackets to bolt the z06 caliper 4th Gen brake brackets, 14" ZO6 rotors, C5/C6 calipers or this back plate kit C5/C6 rear conversion plate kit, ZO6 rotors ?

**98TransAmWs-6** · 06-19-2013, 05:06 AM

Originally Posted by FormulaBird

I didn't know that, I thought they bolted the same. I guess I'll have to mod the spindle.

Interesting that 30 tires worked w/o rubbing, I was going 25 cause I figured the overall wheel diameter would have been 25.41 on the front 275/25/20 and 25.81 on the rear 295/25/20 since I believe our stock diameter is 25.66 so I didn't want to go way off. At 30 the front will be 26.49 and rear 26.96 so a bit off but I guess if it works then I'd rather do 30 for a better ride, thanks!

Do you happen by to know by any chance if I'll need this C6 conversion brackets to bolt the z06 caliper 4th Gen brake brackets, 14" ZO6 rotors, C5/C6 calipers or this back plate kit C5/C6 rear conversion plate kit, ZO6 rotors ?

Those look like adapters and brackets to use Z06 rotors with base corvette calipers. So uf you will be using c6 z06 calipers those kits won't be needed. A company called kore3 sells the correct brackets.

**FormulaBird** · 06-20-2013, 08:26 AM

Just got off the phone with kore3, they had the right kit and ss lines for this setup and I got the correct brackets and also their eBrake kit with the horseshoes, etc. since I may as well change those while at it. They were super helpful and very knowledgeable. However, they mentioned that for doing the rear brakes, I would lose my TCS and maybe my ABS since it may not be compatible. Did you or anyone else have a similar problem with their rear install?

**98TransAmWs-6** · 06-20-2013, 10:37 AM

Originally Posted by FormulaBird

Just got off the phone with kore3, they had the right kit and ss lines for this setup and I got the correct brackets and also their eBrake kit with the horseshoes, etc. since I may as well change those while at it. They were super helpful and very knowledgeable. However, they mentioned that for doing the rear brakes, I would lose my TCS and maybe my ABS since it may not be compatible. Did you or anyone else have a similar problem with their rear install?

I did not install the rears as of yet so I do not have any information on that. From people who have done the rear z06 calipers I didn't think they lost abs but maybe tcs. I don't have tcs so that wouldn't be an issue.