Rim Choice with Dr. Diff's 13" Brakes

SeattleQQ1Fish said
I need some help determining what rims and what backspace to run on my 67 barracuda with Doctor Diff’s 13” brake kit in the front and his 11.7” rears. Rear end is a Strange S-60.

The car will be 1 - 1.5” lower than stock and has QA1 UCAs.

I want to run 275/35/18s in the front and 275 or 295/35/18s in the rear.

I know some have had to machine their rims to fit the 2.7” hub bore, but I’m not really able to do that. Is there a rim you all have had success with?

I run the same brakes up front on my Duster with 275/35/18’s and lowered maybe a smidge more than that. My front rims are 18x9 +35 which is about where you need to end up. 18x9.5” would work too, offset should be in the +27 to +35 ish range unless you want to start modifying things. For a Barracuda the additional concern would be the lower front corner of the fender, it’s more restrictive than Dusters or Darts. The height of the 275/35/18’s is ok but the added width will reduce the clearance on turning.

As for the hubs and modifications to the wheel, it really depends. My Enkei RPF1’s had to be machined. The DoctorDiff hubs are actually a little smaller than the stockers, but are still pretty large compared to other cars. The issue is usually the wheel cap. For example, the hub bore on my RPF1’s is listed at 73mm, which clears the hub. The problem is that the wheel cap is only 63mm, and the hub is so tall that it has to pass all the way through the wheel. So I had mine bored to 73mm all the way through and made custom wheel caps. A lot of aftermarket wheels use a 73mm hub bore, but you also have to look at the wheel cap diameter and how thick the rim is at the mounting surface. Mustang wheels usually have to be machined. Some of the torque thrust style wheels have larger bores, the vision legend 5’s I have on my Challenger are advertised at 83mm and they clear easily. But those are 17’s not 18’s.

In the back, what spec did you use for the width of the S-60? I can get backspace info but I need to know the width of the rear axle. The other thing is if your springs are in the stock location or not. 275’s will fit with the springs in the stock location, 295’s will not on a lowered car without other modifications.