I just swapped on 4 OEM ZO6 18 x10.5's all around with super wide Dunlop 300/660-18 racing tires. Fronts fit perfect but I am not so sure about the rears, it looks very close between the tire and the trailing arm brackets. Have not test drove it yet. Is this my imagination? Anyone running 315/18's or greater on the rear without spacers?
1) It looks like an 1/8" spacer would do the trick, anything special I should know? Any recommendations on where to get them?
2) Is trimming the bottom of the trailing arm bracket an alternative?

Got a really good deal on these very fresh Dunlops and absolutely want to use them.

Depends. What year is your vette?

If the rears are that close, I'd be surprised if the fronts didn't rub at full lock. Also that first tire size doesn't make any sense. I've never heard of a 300 tire, and what is 660? Sure it's not a 315/35 or something?

It is a 1994. The 300 is section width in mm or 11.81". The 660 is overall diameter in mm or 25.98" and the 18 is of course wheel OD in inches.

I run 315 tires on my car all the time. I think some folks have even run 335's. I have Grand Sport wheels. The wheel offset will help move the tire in or out. I have had problems with my tires rubbing the inner fender, but I don't care as it's not a street car. I have seen signs of the tire rubbing the traling arm itself, also.

I'd like to see a picture of where you plan to trim the traling arm bracket to see if it's in a structural location. It may be ok if it's just a flange of the bracket, but if it's structural of course you should not weaken it.

I have got down at Roger Kraus Racing for an alignment and they would take a look at it as well. It would be just the tip of the flange and possibly an 1/8" spacer. I picked up these Dunlops(and spares) very economically(F-R-E-E) after the NASA 25 hour race from Porsche teams and I am going to make it work.

I wouldn't run a 335 on an 11in rim.

I run 335, but they're on an 17x12in rim.

They barely clear the dongbones.

I believe I have arrived at a compromise solution. A 3mm spacer along with carefully grinding the Trailing arm bracket. This should yield about a 1/4" lateral clearance with the Dunlops. I had the alignment done at -2.7 front, -2.0 rear, 1/16 toe out in front, 1/16 toe in on the rear, 6 deg castor. Can't wait to try it out.