Rotor/caliper alignment

I’ve noticed on my front brake, the pistons on one side of the caliper are extended quite far whereas the other side they aren’t far out at all. This seems to be due to the position of the caliper relative to the rotor – it needs some clearance so the rotor itself doesn’t clip the caliper body as it rotates. This means the caliper is mounted to the fork biased to one side, and when I align the pads with the rotor it means the pistons on one side extend much more than the others. Doesn’t seem to affect braking performance and no evidence of sticky pistons.

Any thoughts on whether this is this normal and acceptable or should the pistons on both sides both be extending a similar distance?

Thanks

Dan

Ideally you would have the caliper centered over the rotor. Being off center won’t affect the braking performance but the worry is that the piston may be overextended when the brake pads wear right down. If the rotor is touching the caliper body when the caliper is properly centered, something is wrong.

is it a 2-piece rotor and the inner bit is fouling? maybe get rid and use a one-piece

I don’t much like the sound of the imbalanced pistons but I’m also amazed that the rotor doesn’t “give” enough to allow them to stay centred anyway when/if they move – are you sure it’s not sticky pistons ?

Do you mean the caliper can clip the actual spokes of the wheel, so needs to be mounted outward for clearance, which in turn means the rotor cannot be centred?

It’s generally not normal or acceptable, no – creates problems with noise and brake pad wear. Need to resolve the clearance issue which prob means a different caliper.

Need to resolve the clearance issue which prob means a different caliper

A larger rotor will sort this out if the caliper is rubbing on the spokes.

So it’s when the caliper is mounted so the pads will contact the rotor centrally, the rotor itself clips a bit of the caliper mounting body that is bolted to the fork. It feels like this might be a mounting problem then, just not entirely sure how to resolve it!

This is why the bodgers favourite ‘undo the bolts, pull the lever and tighten them up again’ trick is a terrible idea.

The rotor should be centred in the caliper, not between the pads. If this then means that you have one side touching, its because your pistons are not returning correctly and your brake needs some maintenance.

Hope floating rotors in particular (with the very big rivets) are often problematic for clearance. If you have matching caliper and rotor brand it shouldnt be an issue.  Poor quality or badly spaced hubs can do the same too, if the hub body is not correctly centred as per the standards.

So it’s when the caliper is mounted so the pads will contact the rotor centrally, the rotor itself clips a bit of the caliper mounting body that is bolted to the fork. It feels like this might be a mounting problem then, just not entirely sure how to resolve it!

Got it now – worth checking the disk mounts and adapter for uneven-ness. All official instructions will tell you to clean and face the mounts but the facing tool is expensive, few people would own one. You can still sort out obvious issues with paint or corrosion, or replace a wonky adapter.

Pics would help. What type of caliper is it? Is it the caliper or an adapter that the rotor is hitting? Does the caliper look straight relative to the rotor or is it angled slightly?

Get the R3Pro caliper alignment tool, for whichever brakes you have. Worth getting the piston tool too

thanks all. I’ll take another look at the pistons, I say they’re not sticky but perhaps they are. Will come back on here if there’s something else going on.

I like a good quality set of playing cards

They’re a uniform thickness and same number each side means the caliper is centered exactly

Update for those interested, turns out the pistons were very sticky indeed so I’ve sorted that out tonight, all moving quite nicely now. Also got a new rotor coming as it was due,and the current one is 4.5 years old with a slight kink. Hopefully this will sort it.