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Brucey wrote:thelawnet wrote:...R451 has 'QR wider open'....
aha! That makes more sense than a whole new caliper model number just for a different locknut! Yes, I think you can even see that the pinch bolt assy might swing further on the photos of the back of the calipers. I guess BR-R450 mayn't open wide enough to let a 32mm tyre out when it is mounted on a narrow rim...?
R451 calipers will not allow a 32mm tyre through it with the QR open, we've had to let the tyre down significantly to do so.