I have some 5th gen 20 X 8 front and 20 X 9 rear Camaro SS rims. Be running a quick 9" 3rd gen sized rear end. Do 305 40 R20s tires fit inside the 3rd gens back wheel wells? Any pics? TIA

 

20s are far too big for a thirdgen..

 

The best tire size for those wheels are 245/30-20 front and 275/30-20 rear. You will need 1” spacers all around on a 3rd gen. I agree with T.L., these look out of place on a third gen.

My car during mock up and shake down

 

 

When putting on C7 Z06 calipers on a 3rd gen, there are going to be tradeoffs. The front rotor is 14.6" in diameter on this setup and won't fit into most 3rd gen rims. The front Z06 6 piston front caliper is bigger then the 3rd gen calipers also and needs at least a 19" rim to work. Adding a hydroboost setup to the C7 calipers will make this 3rd gen stop better when compared to a 35+ year old stock caliper setup. I have a perfect set of 20" 5th gen SS rims that I could use, or a 19" set of C7 rims can be found if needed. Rubber band tires and rims sure won't going on the 85 IROC.

 

305/40 is almost 30” tall. It wont fit without atleast some major hammering inner well and likely rolling lip. May want to cut out bumpstop. Usually you dont want to go over 28” tall

 

What's the biggest rotor/caliper that will fit under 18s?...

 

Baer 14” 6P 6 piston inside an 18” Forgeline.

 

Talking to the folks over at Apex wheels they have a 18" rim that will work with the Z06 rotor caliper setup. C7 Z06s came with carbon fiber rotors and the Gran Sports used the same system except with iron rotors. The carbon fiber rotors wouldn't fit in rims that the same sized iron units would fit, so Apex did a 3D scan to find out why. The fitment specialist over @ Apex is very knowledgeable and since these wheels come in different offsets, spacers shouldn't be needed. A lot of 4th gen Camaro owners use Apex products according to the rep. 18 x 9.5 can be used at all 4 corners or the rear can go out to a 18 x 10 or maybe 10.5.

https://apexwheels.com/wheels