Hi, this may be an idiotic question – I fitted some shimano deore brakes to my bike (ragley blue pig with rocckshox revelation forks, 26″ wheels) and have just changed the pads for the first time and it seems that about 5-6mm of the pads aren’t making contact with the rotor. Eyeballing the way the rotor is sitting within the caliper, it looks like there’s a similar amount of clearance, maybe 7-8mm, between the rotor and the lowest solid part of the caliper, i.e. much less than the 20mm that would suggest that I had completely the wrong size rotor/spacer setup.

The frame has universal brake mounts, as far as I know, and the spacers are the ones that came with the brakes, and as far as I can tell are fitted correctly. Any idea what I’m doing wrong?

It’s not normal to need mounts and spacers with Deore. The caliper should go straight onto the mount.

What calipers and rotors models have you got?

It took me a while to realise that my old BR-446 calipers were not compatible with RT76 rotors…

Annoyingly I don’t know what rotors I’ve got because the bike is second hand and I don’t have a full spec. I’ll see what happens if I take the spacers out.

Just tried taking the spacer out and that won’t work. The spacer say “185” on it which makes me think their probably spacers for a weird 185mm rotor.

Annoyingly I don’t know what rotors I’ve got because the bike is second hand and I don’t have a full spec. I’ll see what happens if I take the spacers out.

Can you use a tape measure/ruler? Would you be happy working on the brakes on your car if you have one? It amazes me that just because it’s a bicycle people assume they have the skillset to carry out what is essentially a very simple job IF you know what you are doing.

Sorry, to clarify I know it’s a 180mm rotor but I don’t know what make. I will admit that this is not my finest hour.

You can get Hope 183mm rotors?

Si

Yeah, I think I had some Magura discs that were 185 (might have been my Avid Juicy’s) so it sounds like you need new adaptors…..

Yeah, I was under the impression that rotors were only available in multiples of 20mm, but it turns out that you can get 180, 183, 185, 200, 203 and 205mm rotors.

If it’s definitely a 180 rotor and the spacers are marked 185 then you need to replace the spacers with a 180 spacer.

The make of rotor is irrelevant TBF. Think the revs will take a 160mm rotor without spacers but you need one for the 180mm. Are your forks post mount or Is?

IS. I think I’ve got it sorted. New spacer on its way from the internet. My mistake was not knowing that rotors (and by extension spacers) come in more than 160, 180 and 200mm sizes.