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Brake disc rotor sizes

Roy Stewart2026-02-08 12:00:53

Hi

Ive built a tandem frame with the expert guidance of Jeff Roberts at his frame building academy 

Its getting hydrolic disc brakes.

I'm asking advice on what are the best sized rotors for both from and rear brakes.

Thanks in advice for any help

Cheers

Roy Stewart

Stuart Hunter2026-02-08 12:44:00
if you're rear frame triangle will allow it a 203mm disc rotor is the best standard disk you should aim for. You will need an adapter fitted to the frame to take the calipers the correct distance away for the brake pads to clamp onto the rotor property. The larger the rotor the better the breaking.
David Ross2026-02-08 13:02:28

Hi Roy,

A lot depends on what you want to use the tandem for, all-up weight, as well as where you want to ride it. With disc rotors on tandems, generally speaking, the larger the better, coupled with careful consideration of how the brakes are used.

For example, our experience with 203mm Shimano XT rotors was just about okay in the UK, but very poor in the Alps, with warped rotors despite taking all efforts to keep them cool, and that was with a light Cannondale RT2 tandem.

More recently, on our Moustache e-tandem with its twin batteries and much greater weight, I replaced the stock 203mm Magura rotors with their larger 220mm MDR-P rotors designed for e-bikes (and hence ideal for tandems), coupled to Magura 8.S pads. This combination has proven to be extremely tolerant of tandem-grade abuse and in fact to prove to myself that they were up to the job, we descended the 2000-odd metre Croix-de-Fer using only the rear brake to see if I could get it to fade. I couldn't. I'm really happy with that combination and it's proven to be extremely reliable on Alpine descents, British 1:3s and everything in between. And the rotors make a fantastic ticking sound when cooling down!
 

I've since fitted the 203mm version of the Magura MDR-P rotors to the Cannondale, because that's the largest size that will fit, but I doubt we'll ever take that to the Alps again, otherwise I'll incur the wrath of my cardiologist...

I hope our experience helps. 

Roy Stewart2026-02-08 13:25:39

Thanks for your input guys.

You have given me an idea of what I need.

I'll see what fits the frame and go from there,

Ill' be mostly using it in the UK to do Lands End to John O Groats next year.

Cheers

Roy

Photo of frame attached