Hi All,

I'd like to esteemed opinion of the forum.

I've transferred my old Hope IS-mount brakes to my new road (and light off-road) tourer, built arround a Salsa Fargo frame, via a pair of IS-Post mount adapters. I'd forgotten that IS rear mounts are effectively set at -20mm (that is, a 160mm rear IS caliper will take a 180mm rotor if mounted on the front) – so my old 160mm IS Mini (#3 caliper) plus adapter is now looking at taking a 200mm rotor at the rear.

Clearly, fitting a 200mm rotor is now my easiest option, rather than trying to find a number 5 caliper or selling these (fairly battered) brakes and buying a new set.

Given that this is a rear brake (so total torque is limited by wheel traction), will a 200mm rotor generate enough torque to damage the frame?

Cheers – Adam…

If you are loaded then you will get more braking from the rear but possibly more of an issue might be heat, or the lack of. My brakes work best when they have been used heavily, with such a massive rotor they will effectively just be dragging a bit, don't know if that will be a good or bad thing.

EDIT- that didn't answer your question did it? I hate it when that happens… 🙂

Tracker, what on earth are you talking about? 200mm brakes will be less powerfull because they won't heat up? Have you been watching a lot of F1 or something? 200mm brakes are more powerfull because the braking surface is futher away from the hub creating more torque, which is why he's asking.

EDIT: Oh, and I haven't answered the question, but I'd check with the frame manufacturer, as they're more likely to know.

will a 200mm rotor fit in the frame? not convinced one would fit particularly well in my 130mm trail bike…

Hey all,

If you are loaded then you will get more braking from the rear

Aye, that's my big worry – coming down a big hill on tarmac fully loaded up, it's going to take a lot of torque to make the rear wheel break traction… Question is: can the frame stand that level of torque? I'm waiting on a response from Salsa, but interested in opinions from here.

Having said that, it's built for a 160mm rotor, and I reckon I could make the rear wheel break traction under those circumstances. I guess the big difference between front and rear is that the traction increases at the front under braking, whereas the point at which the rear tyre loses traction is going to be largely constant irrespective of the retarding torque and probably much less than the maximum torque any sized rotor can apply…? Does that make sense?

will a 200mm rotor fit in the frame?

Yes, with some room to spare.

Cheers – Adam…

I see where you're going with that, and to some extends you're right, but I'm pretty sure with having the caliper further away from the axel you're increasing the rotational force that is applied on it. It's not the force required to stop the wheel, it's the twisting force applied on the seatstay, or wherever the disk tab is.

I'm sure an engineer will be able to put it in better language, or debunk what I'm saying.

Tree-magnet, I wasn't that clear was I really. Mine are less noisy and feel better when I am having a go but what I failed miserably to say was that if I am not on it and just mincing about that is when I destroy pads in short order. Am sure that there is an optimum but if they aren't working hard enough (and hard enough might be more than the frame likes, still not answered that question) then they might also just eat pads. Rapidly spending all the money saved by using a brake you already have.
Is this when I should say "my bad"? Never really got the hang of that phrase…