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Old 2018-06-28, 01:19 AM   #1
unicycleharry
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Disc Brake Alignment/Adaptor

My disc brake pad isn't completely over the rotor.
I recall that someone had a similar scenario, and the adaptor was upside down, but I can't figure out what I might have done wrong.

This is a 160mm rotor, and I think the adaptor came with the brake caliper.
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Last edited by unicycleharry; 2018-06-28 at 01:20 AM.
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Old 2018-06-28, 06:56 AM   #2
kunstrasen
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Are the brake and rotor from the same maker? Depending on brake pad width, different makers use different width of the friction ring on the rotor as well. At the end it is important that the complete brake pad is on the rotor when braking. That is hard to tell from your pictures.
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Old 2018-06-28, 11:01 PM   #3
unicycleharry
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There's a tiny bit of the pad that doesn't touch the rotor.
I did a quick 30 minute ride and here's what the pads look like.
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Old 2018-06-29, 06:13 AM   #4
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Braking itself will be fine like this. However there is one thing to consider. If a part of the pad is remaining, this part will touch the opposite pad at some point instead of the rotor. Then you have to replace pads, even they are not completely worn out. So you waste pads compared to a proper setup. Not such a big deal as on a uni we are not brake pad eaters like a DH bike in bad conditions .

You cold grind down the IS to PM adapter a mm. However that is kind of dangerous, as the PM surface needs to be exactly rectangular to the IS mounting holes, otherwise the brake caliper is not in line with the rotor which leads to bad brake power and might create noise.

Sometimes it helps to use another IS to PM adapter. They are slightly different from maker to maker. E.g. the Shimano ones are quite cheap, so that might be a try?
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Old 2018-07-01, 10:28 PM   #5
mowcius
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This is reasonably common as the disk position depends on the spacers used between the bearings and spirit cranks.

I believe that the KH hubs and cranks use 6mm spacers, which should put the disk in the right place. Using larger or smaller spacers may cause you to not have enough movement on the brake to be able to get it central. Spacers should however be the correct size to suit the crank/hub combo, so the solution here is to shim the adapter with washers.

A washer or two between the frame mount and the IS adapter should get the calipers in the right place.

Running it like it is, brake performance will never be optimal as when you put the brake on, it will be trying to bend the disk into the middle. It's something you see a lot with badly set up disk brakes.
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Old 2018-07-02, 02:03 AM   #6
unicycleharry
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mowcius, thanks for pointing that out. I noticed the left/right alignment issue and added washers to center it better.

My initial question was the caliper's radial position, as it seems to sit about 0.5mm to far away from the axle.

kunstrasen, thanks for the tip. I will use it for now and inspect it every so often to see if the pads ever touch where they aren't wearing down.
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Old 2018-07-02, 12:28 PM   #7
mowcius
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As well as IS to post adapters sometimes being different from manufacturer to manufacturer, disk sizes are also often not the same.
Ideally you'd use a disk designed for your caliper, or at least one from the same manufacturer.

Due to how they're wearing slightly on an angle though, I wonder whether that caliper's not really designed to run with 160mm disks, or whether the M4O mount is slightly off the standard spec.
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Old 2018-07-02, 02:23 PM   #8
bouin-bouin
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No issue on my 29 with M4O frame + 180mm disc (disc on the left side of a Nimbus Oracle hub)
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