Originally Posted by
Bob Dopolina
If you design a disc specific carbon rim it means there is no brake track and that frees up design considerably - especially if you are designing tubualrs.
For instance, you could go wider and taller on the tubular bed which would alter both the contact patch and the interface between the tire and the rim. I'm sure there is a lot of room here for aero improvements. I'd image that guys at companies like ZIPP would LOVE to have this design restriction removed and be allowed to rethink this entire elemnt of rim/wheel design.
The weight of added spoks need for disc application would, most likely, be offset by the material not needed for brake tracks. It would pretty much be a wash.
To those only thining about stopping power your view is too limited.
Big John nailed it when he talked about long mountain descents. Caliper brakes give you Popeye forearms half way down the mountian and it only gets worse with brake fade. Add rain and carbon rims to the mix and it's an issue worth addressing.
Cheers, you raise good points. But I still have reservations about the idea, because to my mind cable disk brakes don't have the modulation or power of hydraulics, and tbh I wouldn't change from rim brakes to cable disks - it's just not worth the bother, I don't think you'll gain that much. You can still burn your arms out braking using cable disks, it seems the expectation gap with disks is running away with people already.
WRT rim design, there will likely be another design restriction that we just don't know about yet...once a rim/tyre combination goes past a certain point, there may be diminishing aero benefits, if you remove the brake track the wheel may need reinforcing elsewhere, and while it may free up rim designers, (who wouldn't like a challenge like that to work on?) your assumed benefits have to overcome the fact that, on the front wheel for instance you'd have to nearly double the spoke count and add a rotor. This may be different for companies like Mavic and Fulcrum, who may be able to add fewer spokes because of their spoke design, but still that's a long bow to draw.
There may be tremendous advances in cable disk brake design, that I just don't know about and that make all my points moot. Also, if you're making long descents in the wet on carbon rims with a carbon brake track you probably need your head read, there's no safety device like common sense. I have a light, old aluminium box section tubular with a ton of spokes I use for rides like that. Brakes great.
I'm going to stick to my guns for now, that until there is a solution that allows hydraulic brakes to be used on a road bike the jump isn't worth making. I'm 99 per cent sure that at some point I'll be proven wrong, but who can't say that.
EDIT I'm only commenting on road race bikes. Cross bikes, tourers, tandems they've been around for ages and are a done deal.