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My road bike has Shimano dual-pivot caliper brakes like these. enter image description here

Whenever I remove or refit the mudguards, or even sometimes just getting the wheel out, they seem to go slightly off-centre, by which I mean rotated around the mounting.

The effect of this is that, when the brakes are applied one pad contacts the rim before the other. Looking carefully the wheel also moves a little to the left or right as one pad pushes it to the side.

I try to rotate the brakes so that both pads contact the rim at the same time to minimise this movement, but as the act of tightening the mounting screw also rotates the brakes slightly, this is tricky.

So the question is - does it matter much if one pad makes contact slightly before the other? What are the likely effects of it doing so?

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All styles of brakes are fussy in this regard, even seemingly "balanced" ones like center-pull cantilevers. If one pad contacts slightly ahead of the other it makes little difference (other than a miniscule amount of unbalanced wear) since the other pad is then pulled in before any real force is applied. You mainly want to assure that the pads don't drag while riding. – Daniel R Hicks Jan 12 at 12:17
Thanks, that's good to know. – James Bradbury Jan 13 at 6:45

2 Answers 2

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The danger of this is your rim may begin to rub the brake pad – especially when you put in hard out-of-the-saddle efforts.

In theory, if your caliper has become off-centre then one pad will have come closer to the rim and the other will have come further away. You should simply be able to push and rotate the caliper by hand back into a central position without loosening (or tightening) the retaining nut. Pull the brake lever a couple of times and if the caliper does not return to a central position, your brake requires balancing i.e. one pad is moving more than the other towards the rim and causing them not to touch the rim at the same time. The other effect of this is it may cause the caliper to rest off-centre.

There is a small balancing (tensioning) screw on top of the caliper. Turn this left or right until both pads move the same amount to the rim.

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It doesn't matter a lot if it's slightly off. But you should be able to center the calipers by hand, even after the mounting bolt is tightened. Just grasp the two brake arms firmly and rotate the entire caliper a bit (with no pressure applied to the brake lever). In my experience this is usually sufficient to get the caliper centered enough. Riding for a while will sometimes help center them as well.

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