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My son's bike has an issue with the pads not fully contacting the disc, resulting in a lip forming on a corner of the pads. This seems to be down to the angle of the caliper rather than a mismatch in diameter i.e. the pad isn't sitting tangential to the disc edge. If I fitted a slightly bigger disc, I think the disc would foul the caliper at the back before it it made full contact with the pad at the front.
Brakes are SRAM Guide, both ends sitting on 20mm adapters. The bike was second hand, so I'm not sure what is original and what's not.
Are there different flavours of 20mm adapter that will put the caliper at a different angle?
Possibly adapter is upside down?
Brakes are SRAM Guide, both ends sitting on 20mm adapters.
Are they definitely 20mm adapters, rather than adapters for 203mm discs?
Front adapter on the rear?
I had a similar issue with the original Guides on a Trek Slash. In my case it turned out the rear mounts on the frame needed to be filed down slightly to resolve the issue - as confirmed by my LBS Trek centre and their warranty process. So it is possible that the frame could be at fault (but hopefully not!).
Mounts need facing by the sounds of it. Warranty job on a new bike…
Possibly adapter is upside down?
They look pretty similar either way round, but the symptoms sound like having it the wrong way round.
Thanks for all the replies. I should really post some pictures
Are they definitely 20mm adapters, rather than adapters for 203mm discs?
That's certainly possible, although I wouldn't expect that to significantly change the angle of the caliper.
Front adapter on the rear
Quite possible, but is there a difference? The front is being spaced from 180 to 200, and the rear is 160 to 180, but I thought either way you need a +20mm adapter.
Mounts need facing by the sounds of it. Warranty job on a new bike
No, one end of the caliper needs to be 1-2mm closer to the bike. It's not a facing thing.
Possibly adapter is upside down?
They look pretty similar either way round, but the symptoms sound like having it the wrong way round.
It's the kind of adapter where the adapter bolts to the frame, and then the caliper to adapter, so the caliper is offset as well as raised. I can't see a way to fit it wrongly and still having it looking even vaguely right.
I'll get some photos when he's back from school.
I've had brakes where I've needed to add a washer or two between the calliper and the adapter. While brakes are supposed to be set to a standard it doesn't always work exactly. Maybe some manual adjustment like this will get yours better aligned.
It's the kind of adapter where the adapter bolts to the frame, and then the caliper to adapter, so the caliper is offset as well as raised. I can't see a way to fit it wrongly and still having it looking even vaguely right.
Probably not upside down then, some +20 adapters are just spacers that use longer bolts to go straight through to the frame which definitely can go on the wrong way although usually that results in them not working at all.
My gut feeling is you've got a caliper that's set up for 203 or 205mm rotors and a 200mm rotor. My solution in those cases is either swap the adapters around which what's in the spares box until it works. And if it doesn't then fit a bigger rotor and then if the caliper fouls the rotor add some 0.5mm shims under the caliper until it clears.
If it’s a new bike then contact the shop. Without physically seeing the problem it sounds like the mounts need “facing”. The shop should have a tool that will machine the mounts so they are parallel to the axle and correctly spaced. Hope do some precision spacer washers if required. Hope this helps.
My son's bike has an issue with the pads not fully contacting the disc, resulting in a lip forming
My ebike has a similar issue where the rotor doesn't touch the last mm of the actual pad, guessing it's a 200mm rotor and the adapter is meant for a 203mm. The brakes are absolutely fine so I just ride the bike anyway, that would be my advice if op's brakes are working
The brakes are absolutely fine so I just ride the bike anyway, that would be my advice if op's brakes are working
They're fine until they're not 🙂 My son reported that his front brake wasn't great. Turns out the pads had worn to the point that the lips on the pads were touching each other so it wasn't squeezing the disc properly.
The brakes are absolutely fine so I just ride the bike anyway, that would be my advice if op's brakes are working
...you'll get less use out of each set of pads if you do this and some unpleasantness when the unworn parts of the pads start to touch each other.
They're fine until they're not 🙂 My son reported that his front brake wasn't great. Turns out the pads had worn to the point that the lips on the pads were touching each other so it wasn't squeezing the disc properly.
I first noticed this issue when I changed the pads, thinking they had lasted longer than I expected and found both were down to the backing plate on the part that had actually been in contact with the rotor. The brakes did still stop me but obviously weren't the best on the last ride before I noticed, I've no plans for changing adaptor or facing the mounts but to be fair I'm the only one that's going to suffer the consequences of the brake failing if and when it does
Taken me a little while to get back to this. Turns out I'd misremembered the front and assumed it was the same as the back. The front is indeed the kind of mount that simply slots between the caliper and fork with longer bolts and it was on backwards, so that one was easy.
The rear remains a mystery. This is the set of pads I just removed:
As you can see from the wear, it's not that the whole pad is too far out, it's that the angle doesn't match the disc.
Here's the caliper and spacer:
Disc is 180mm and I assume the frame is 160mm.
I'll try swapping to a different spacer, but I'm curious to know what this spacer might be for, as it doesn't seem to be a simple +20 spacer.
That looks like it moves the caliper forward rather than up. First thing I'd try is putting the 20mm one that's currently on the front to the rear temporarily and see if that cures it. Assuming you don't have a normal spare one anyway.
That adapter looks the wrong way round to me. I’d be turning it 180° and see if it lines up better.
Thanks for the replies. I think I've finally figured it out. After a bit more Googling, I've not been able to find anyone selling an adapter of this shape, but it does seem to be standard on this bike which is a Propain Yuma 24"/26" convertible frame, and which I now remember has swappable drop outs for the different wheel sizes. I think this weird adapter is to align the caliper with the 24" axle position. This bike had been converted to 26", but it looks like the brake adapter wasn't swapped for a normal one.