I have a Cannondale CAAD 10 disc frame and a pair of BB7s that are 160mm rotors.

They do not fit because (I think) I need post mount spacers.

What size rotor does the frame expect, and hence, what size spacers do I need?

1 Answer 1


The frame comes stock with 160mm rotor in front and a 140mm rotor in rear and uses a spacer for the front post mount only.

From this link, it looks like you need the 20p spacer, which Avid says is OEM only. However the spacing dimensions are 12.5mm top and 7.5mm bottom. You can probably find spacers of those dimensions to mount it without the OEM spacer.

I have the same bike with a 160mm rotor in front and I can confirm the dimensions are 12.5 top and 7.5 bottom and it looks like spacers would work as well.

Here is what the spacer setup generally looks like - 160mm with OEM spacer on front, and 140mm mounted with no spacer on rear.


rear spacer

  • Thanks! So have I got this right.. I have the same rotor as stock for the front and need the spacer. I have 160 instead of 140 for the rear so will also need a spacer for that. Can I use the same spacer for both, and is this the one I need on-one.co.uk/i/q/BSAVPPBM/avid-post-to-post-brake-adaptor ?
    – Adam
    Commented Apr 5, 2016 at 18:46
  • Just go 140mm all around, no spacers needed. 160 is overkill for me.
    – ebrohman
    Commented Apr 5, 2016 at 18:48
  • I will consider that, but I have the brakes to reuse already, so if I wanted to?
    – Adam
    Commented Apr 5, 2016 at 18:49
  • Look at that avid chart, I think the rear spacing dimensions are different so using the same spacer for both may be out of the question. Also it may be more trouble than it's worth trying to source the spacers. Avid sells a two pack of rotors for a pretty reasonable price. Your bike will also look better with 140's, if that's something you care about.
    – ebrohman
    Commented Apr 5, 2016 at 18:52
  • Yeah, I think you're right, if I can find a pair of 140mm rotors, it will be simpler and nicer. I won't need the extra size anyway. Thanks.
    – Adam
    Commented Apr 5, 2016 at 19:00

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