The only reason that's tested is that the shims keep your pretty fixed calipers from changing colors.
I had the shims with my first set of pads and they lasted a long time. The second set of pads went pretty fast and I did not have the shims. Both pads were PF01s.
I also want to test the theory that PFC may have some consistency issues with their pads. I've never really gotten an consistent wear rate. I'm trying some pagids and stoptech pads so I can compare.
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