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I am thinking about getting a second wheel set for my CX bike to be able to easily swap between road and off-road tires (and possibly run a tubeless setup). The bike is equipped with 12mm through-axles (front and back) and flatmount brakes.

I am wondering (assuming same disc diameters): Would the disc rotors be exactly[1] in the same place laterally, or would I have to adjust the brake caliper position after changing the wheels? Would it make a difference if I got the same/different brands or models of wheels/hubs?

[1] exactly: close enough, so that the brake pads don't rub on the rotors ;-)

  • It is. Neutral support mechanics in races are counting on it. But some small rub can occur due to the tolerances which I am not familiar with exactly. – Vladimir F Oct 14 '19 at 14:35
  • CX and road disc-brake wheels are perfectly swappable You'll need the same disc size and axle standard, of course. – Carel Oct 14 '19 at 15:30
  • Reportedly, one of the reason pro team have been slow to adopt disc brakes is because there is some margin of error from bike to bike, so team mechanics need to shim the discs so that any given wheel can be used on any given bike. I don't know what that margin of error is, and it seems that once you've got it dialed in, you're done. – Adam Rice Oct 14 '19 at 16:55
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In my experience the answer is kinda yes. You won't need to re-align the calipers with every wheel change, but you will likely need to adjust the brake pads. Hydraulic brakes make the process easier since they are self-adjusting. On bikes with mechanical disk brakes you will likely need to adjust the pads with every wheel change.

In theory, every 6 bolt rotor and centerlock hub should put the disk in the same place and plane so that this should all just work. In practice the tolerances for disk brakes are so small that even slight differences will cause the disk to rub on the pads. There are two main reasons for this.

Brake disks aren't flat and don't stay flat over time.

The surface you mount the brake disk on isn't flat.

Centerlock was created to help with the second problem, they do seem to be a bit better at staying interchangeable than 6 bolt. The only way to overcome the first is to get good at brake disk truing and work to get the disks on your rims all the "same".

Having said all this, you can get your wheels "good enough" that swapping wheels can be pretty straightforward. But it's unlikely that will happen out of the box and keeping the rotors true enough to keep your wheels swap-able does take some ongoing maintenance.

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    The easiest path is probably getting wheels with the same model hubs and rotors. That way you only have to deal with rotor wear. – Argenti Apparatus Oct 14 '19 at 17:23
  • It depends on all the components. With narrow gap SRAM calipers, QR, and fit and finish of my frame I cannot even get the same rear wheel out and in again without causing rub. – gschenk Oct 15 '19 at 12:50
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I can swap the wheels between my tourer and hardtail with no need to even adjust the mechanical disc brakes (or the gears - both are Shimano 9 speed). In the past I also had a second front wheel for the tourer.

All 4 hubs are 6-bolt, from at least 3 makes: rear Shimano and (I think) Joytech, front SP (dynamo) and (I think) Shimano.

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