I was just reading the 1967 chassis service manual yesterday. I was concentrating on the implal information but it and the chevelles both had the optional two piston caliber disk brake option. The manual said that 15 inch ralley wheels were mandatory for that option. I know I had to use 15 inch wheels on my 67 chevelle after putting disks on front and rear. Hope this helps.
The 15" wheels were included with disk brakes on the full-sized cars only. The Chevelles, Chevy II/Nova,and Camaro still used 14" wheels as standard with disk brakes. BTW, Rally wheels were standard with and exclusive to disk brake cars in '67. For '68 Rally wheels were still standard with disks, but were now optional on drum brake cars as well. For '69 (and possibly some late '68 models) the Rally wheels were no longer standard on disk brake cars.
15" Rally wheels debuted on Chevelles in '69 with some Yenko SC (COPO). They didn't return in that size on Chevelles again until the '74 Laguna type S3 and/or radial tire option.
The standard '67 14" rim would not clear the caliper. When you ordered disc brakes on a Chevelle you got the 14" rally wheels which would clear. You could also order the rally wheels without the disc brakes but the centre cap didn't say disc brake on it.
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