i know a guy who fitted 312mm brakes & he had bbs rx2's 16" on he said he grinded the caliper down abit (is that safe to do?) or will adding a spacer be better? (i have the bbs rx2's & need to upgrade my braking to 312mm so was thinking about the spacer?
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I have RXIIs on and 312mm frakes...and you need to do a fair bit of work.
You do indeed need to grind the high spots off the front calipers...probably 4-5mm...at two points on each caliper.
You can't run a spacer - unless you are running 50mm spacers - because it's the thick section of the rim where the 16 M7 bolts thread in, that catches on the caliper.
Even if you get them to fit, it's feeler gauge close...so close in fact that when you brake, the caliper flexes and it'll remove the paint/powdercoat from the inside of the rim.
If your wheel is slightly out of round..you've got no chance.
In all honesty, 288s with DECENT pads, fluid and discs will give you almost as good braking, with none of the clearance issues.