disc brakes for rd [what are they like?]

Ok, so the surfaces are different, but my point was more that all the design issues being thought up have been answered. It's not beyond imagining a brake attached to an axle withe cable coming out the end of the axle and up the fork/stay, clamping onto a disc attached to the inside of the hub. The hub body would need to be the size of a rotor and changing pads would be a major pain in the arse.

Not sure about the aero saving or weight, but would be totally weather/mud proof!

Sounds hot.

I mean, too hot.

...and still...

you have to react the brake torque closer to the axle, making the bending moment on the end of the fork blade even more concentrated than it is with normal disc brakes.

Yeah totally fails to answer your original question of could you put discs in hubs to make strengthening the fork less of an issue.

Just made me wonder why they don't make better hub brakes, by making them basically disc brakes...

made me wonder why they don't make better hub brakes, by making them basically disc brakes.

Cooling is the main problem. It's easy to cool a drum, the friction surface is in intimate contact with the shell and you can easily add fins if necessary. Getting good thermal conduction from the thin edge of a disc to the hub shell is more challenging.

At high speeds, you can add ducting and make the disc rotor into a centrifugal blower to force cooling air through it, see F1 car brakes which are essentially entirely shrouded by the wheel (also, they are crabon, so they actually have higher friction as temperature rises up to a point, unlike metal rotors)

Sticking a ductile iron or stainless steel brake rotor inside the hub is a recipe for brake fade at best, and brake fluid vaporisation at worst.

Shimano want brands to use 140mm discs. They're worried 160s are too powerful.

I think every brand so far using their system has gone for 160mm discs. I wonder if this is because this allows the caliper mounted further up the fork, helping keep the fork stiff and light(ish)?

Small discs, torque on the axle but through both fork blades. Big in 2017!

Don't believe mechanics... they will always tell you that everything is crap. Road discs are not more powerful than rim calipers, they are just more reliable in all conditions. I had them for 5 years now and I would never go back to scored rims and dodgy wet-braking. The drawback are insignificant compared to the advantages. Drawbacks are: pads last less, pads need frequent adjustment, pads can crumble when they get towards the end of their life (can be dangerous, so replace early!) the systems is over a pound heavier

I think you are thinking to literally, instead of a thin disc attached to the inside of a hub, how about a disc sized hub and using the internal walls of the hub (maybe with some replaceable cladding) as the disk. Piston pushing two pads away from each other rather than clamping.

Build it like that and you have to make the walls very thick to resist bending. We clamp thin discs between a caliper because squishing a little bit of plate is structurally simple. Re-lining is also pretty easy with drums, but getting a flat plate of friction material to stick to a flat plate of hub end plate is much harder. These are not insoluble problems, or we wouldn't have disc clutches, but they are solutions to problems your design creates without having any countervailing benefits.

Ooh, countervailing... Nice word.

Pointless, but nice.