Disc Brake and Wheelbase Adjustment

Lengthening the wheel base or chain stay length on the Origin8 CX700 frame and re-aligning the brake caliper to the disc.

Factory specs list the frame at 428mm chain stay length, but there is a ~20mm long slot for chain length adjustment for single speed operation. Over the years, I've gradually tried moving the axle back at least as far as the disc brake caliper will allow.

I must have pushed it a bit too far the last time I tried this as I pushed the brake disc beyond the pads in the caliper leading to uneven pad wear. I found a different caliper adapter in my box of parts that results in tipping the caliper up at more of an angle. This lets the body of the caliper clear the material of the adjustment slot which in turn lets the caliper move back farther to line up over the brake disc. I also had to grind a few mm of material off the front edge of the adjustment slot.

The end result is gaining ~10mm of wheelbase or chain stay length, up to around 445mm and restoring full rear brake operation. Also, I now more fully understand the interactions of moving the brake rotor and moving/rotating the caliper on this frame. That's one issue in building a bike from the ground up, there's no "Owner's Manual" to refer to for adjustments like this. You have to go back to first principles and figure how it should be done. This being my first bike with both disc brakes and a horizontal dropout, it took a while for these details to make sense.

As you move the axle and rotor back, the pads in the caliper contact the rotor in a different part of it's arc. So you need to also rotate the caliper with a different IS adapter to re-align the pads with the rotor braking surface, on this bike going from 0mm to 20mm did the trick. If I had been running canti brakes, this would have been done with adjusting the brake pads, very easy to see that. With the disc brakes, those pads are buried inside the caliper and it's very hard to see how they are contacting the rotor.

Yes, I know this slotted dropout is intended for chain tension adjustment when running single speed where you have no RD to take up chain slack. But it's there and it can serve another purpose. There are the small axle stop screws inside that hold the axle from moving forward under pedaling pressure. You can see the mark on the dropout slot where my axle used to run.

More to come...
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