I'm working on a 2024 Dolan Ares road bike. I need to upgrade the rear brake disc from 140mm to 160mm. There only seems to be one style of flat mount rear caliper spaces to go from 140mm to 160mm and it does not even come close to mounting the caliper in the proper position.

With the 160mm rotor on the wheel and the wheel mounted on the bike and the caliper sitting where it would need to be mounted, the caliper is sitting just over 11mm above the face of the original mounting surface on the frame, and the bolt holes in the caliper are sitting roughly 3.5mm forward of the bolt holes in the frame.

Does anyone have any suggestions for a solution?


Mount Spacer

Roughly where caliper needs to sit

HPBikes: With reference to your second photo above, the brake caliper should be positioned lower and further to the left. The caliper bolts onto the spacer through the two bigger holes, and the frame bolts onto the spacer through the two smaller holes.

Except you have it aligned to the original mounting holes - it needs to move forward, not just up, to contact the larger rotor properly.

Thanks for the info. I was able to get it all sorted. The bolts to bolt the adapter onto the caliper were a bit tricky to find as the larger hole in the adapter was .3mm smaller then what seems to be standard head diameter, 9.5mm for the M5 - 0.8 button head socket cap screws. Anyways thanks again everyone, much appreciated.

Have you tried contacting Dolan? I've found them to be both responsive and helpful.

What's forcing you to "upgrade" the rear rotor to a larger one? What size rotor is on the front wheel? What is this "upgrade" going to do for you that the 140mm rotor didn't already do?

It's trivially easy to reduce bolt heads - just spin the bolt in a drill and grind it on a bench grinder. I don't know why you'd be using button heads in this application though, do you mean low-profile cap head?