I know I am missing a rotor but I don't know what to attach it to

Question

I got a cheap second hand bike for my son as its not worth repairing his current one as he outgrew it. At the time, I knew it needed a new inner tube which I was going to replace.
Only now I noticed that the front brakes don't work. I can see they are disc brakes but the disc is missing. The only disc I can get locally has mounting holes. The bike has nowhere to mount it to. The calipers? open and close just fine.
I thought about changing the brakes to the type that works against the rim but the problem is the same and there is nowhere to mount those brakes (holes are missing and I don't want to make them)

Click images to embiggen
Assuming I can install a disc rotor do I need to get a specific kind or something else to mount it to? Do I actually need a different rim?

David D · Accepted Answer

You will need a wheel with a hub that is rotor compatible and fits your bike.
There are two main ways to mount a disk brake rotor to the hub.
A Shimano centerlock design has splines on the hub to allow a rotor to be attached.

Or a six bolt rotor mount

Your front hub does not have either of these mounting methods. If the fork is original to the bike then it is likely that the wheel is not.

Carel · Answer

Fortunately the brake is a cable-actuated non-hydraulic brake and you don't need to worry about fluid loss in this case. The hub looks as if it might have a lock-ring for the disk (that serrated ring on the left next to the spokes), but I'm not so sure when looking at the blown-up picture. In which case you'd need a new front wheel, unfortunately.
If there is a lock-ring, all you'd need is a fitting centre-lock brake disc, probably a 160mm version and a lock-ring tool. Both are quite inexpensive. It's not rocket science to install it and there is a number of how to videos on YouTube. Check the brake pads as they could be missing as well or be in a poor shape and adjust them.

Armand · Answer

From what I can see, there is no serrated ring and the hub is not a disc-brake compatible one (for either center lock or 6-bolt rotors). Thus, for disc brakes you'll need a new wheel that mounts one or the other style of rotor. The rotor will cost probably an extra $20 or so if the wheel doesn't come with one.
It's hard to tell from the photos, but your wheel may have the flat surface next to the rim needed for V-brakes (pics, please). As you note, the issue is then mounting rim brakes.
We'd need photos of the whole fork, especially of the front just below the "crown" area where the Y of legs starts. If you have brake mounting bosses there, or threaded holes for them, it should be quite straightforward to mount V brakes. Decent quality Shimano V brakes run about $15-20 online in the US.
PS - I'm assuming this bike is a 26" wheel mountain bike - it would be good to know the wheel size for sure.
PPS - As wheels can be fairly expensive, in the past I have been known to buy a cheap used bike just for the wheels and then resell the frame.
Update: Thanks for the bike photo! It does seem to be a Walmart-level bike ( https://www.canadiantire.ca/en/pdp/supercycle-ascent-full-suspension-mountain-bike-26-in-0711038p.html ) and with no mounting holes for V brake bosses as you mentioned, I think you're stuck with buying a 26" wheel with disc brake hub and rotor. On the good side, a decent front wheel will make for safer riding and stand up to disc braking forces, and you can always keep it or sell it once your son outgrows this bike.

I know I am missing a rotor but I don't know what to attach it to

3 Answers

Add your own answers!

Ask a Question