Dave Kirk:

"I think the real key to generating sales will be getting riders to fully understand that the advantage of any wet brake (and discs in particular) is one of feel and modulation. Car and motorcycle enthusiasts have been thinking about this for a long time and have gotten past the "the wheels will lock - how much more do you need?" question"

Seems like most cars have onboard computer controlled brake systems to prevent lock up so until bikes have this feature(which is not out the realm of imagination) probably not comparing "apples to apples" using this analogy. IRC the difference in lap times between Formula 1 cars and Moto GP motocycles on the same course is not that the cars are so much faster but that the contact braking "patch" is much larger on the cars; the quicker lap time of the F1 is due to braking ability allowing a deeper entry at speed into turns. The contact are of a bike tire is pretty damn small as far as braking goes, not sure how this relates to anything though!

I have a v-brake(cool stop pads) road bike and a rigid mtb(converted to road use with 700x32 tires) with discs, 2000-2001 year model XT with 6" rotors, but I don't know that discs give me that much more, if any, braking power/control. I'm 245lbs but only ride in the rain if I'm out and get stuck in it so I can't speak for wet comparisons, although I'm postive the discs would be hugely better in those conditions.

This thread pretty much veered off topic from the OP didn't it? Although in this case thats a good thing:thumb:

cheers, Brian

Care to elaborate?

thanks, Brian

Dave,
Thanks for posting in such detail. I think your reasoning is sound.

I hear you. Before the real advent of ABS it was a bigger challenge to get the brake modulation and force distribution right.......at least compared to now when the computer can handle much of the 'at the limit' behavior.

But even with ABS modulation and feel are still a very big deal in a sports car - the 'before the limit' stuff is nothing ABS can take care of. In other words being able to step right up to the point where the ABS will kick in but not activating it is important for driving at the limit and just for fun. I race a lot of autocross and one of the biggest challenges in setting up the car was getting the modulation and force distribution right. Once I did my lap times really dropped.

But even before I got the braking sorted in this car it had more than enough power to lock the wheels (or more like trigger the ABS) at the flick of a toe.............now I can bring it to the brink and keep it there if I wish...........or with a bit more pressure dive into the ABS. A beautiful thing for faster lap times.

Fun stuff to think about.

dave

Group; Great responses to the pokey post. Several posters offer new views I simply had never thought up myself. Tech wise, I do think the future bodes well for disks in general on singles and on tandems and cost will drive to being appropriate to need. Now, will disks take over the world...probably not, but I have no crystal ball on that.

Arrival of better brakes (no matter the shape or format) is a good thing. Reasonable priced welcomed also.

For tandems (and maybe heavy rider/heavy touring), I am already redoing my designs to put braze-on's in the right places to support front/rear disks plus front/rear canti's. But I am switching the canti braze-ons from the classic/Mafac type fixed studs to the new screw-in studs (for market flexibility and price point targeting). I really like the idea of being able to switch back and forth between hub braking and rim braking during a steep descent and thus finally defeat the functional ills and the failure modes of both types of brakes.

Once fully integrated, I am initially wagging that the weight penalty would be well under a pound, which is not very important on a loaded touring tandem. If we consider that the rear disk would dual-purpose as a classic drag brake. I am looking at how I might "dual cable" the rear disk's caliper to give the stoker a lever on it as well as the Captain dual lever. Shouldn't be rocket science, but modulation has to be tested and designed to be adjustable between the riders levers. I still think the Captain needs to be able to lock up both wheels, but that the stoker shouldn't be able to lock up the rear wheel... a discussion to be left for another day.

Thus by then removing the weight the separate drag brake in the equation (an Arai drum is heavy) puts the numbers down into ounces (or maybe a net reduction) and the total added labor at about 2-3 hours per frame (labor should go down over time). I think it will be a good design in the end and at worse case, won't take anything away from an otherwise good tandem.

Thoughts?
/K

Your not seeing much of a difference between the v-brake with good pads and the disc brake, here's how you can improve on that. Fit larger rotors front & rear, plus switch to SwissStop green disc pads. Unlike off road riding where traction is poor and large rotors can sometimes be touchy, paved surfaces provide greater friction, increasing rotor size will improve modulation with low lever effort in this condition, especially with the load you're imposing. The advantage the SwissStop pads will provide is improved modulation also. Their pad compound of various material constituents is a little more forgiving than metallic pads, and far more fade resistant than straight organics, plus they're quieter than either. You also may be equating the outright power of the v-brakes with braking performance. If that's what you prefer, metallic pads will probably provide the bite you're looking for.

How this relates to the OP's question about what to plan for, is build for large rotor clearance. While it may be the small rotors SRAM says are adequate for their new system is valid, it may be the OP's needs exceed the limits of 160/140 size rotors in his application, and/or with whatever components he uses.

Two sets of braze ons? Seems like sensible forward planning. With a road bike it would then make sense to have a standard bridge ready for a rear calliper, even if not used?

If you did need a bigger rotor than the SRAM suggested 160/140, then wouldn't your priority be the front? That is where you'd need it, right? So it would be a fork issue and the design of the rear triangle less important (ie you are not likely to need or benefit from making room for a 180mm rotor out back)?

I wouldn't want to over tax either end. The rear is there to share the work load.

I use a 180mm rotor on the rear. A 140mm was completely inadequate for prolonged use. The pads glazed frequently, the rotor turned blue, and after straightening the rotor when warped, it would return to its malformed shape in a couple heat cycles. When pads overheat, modulation and grip are lost. A 160mm rotor was an improvement, but noise, and occasional pad glazing remained. Based on my experience with steel rotors, mechanical calipers, conventional backing plates, and my braking demands, I don't have faith in the possibility a smaller rotor on the rear would be adequate for all riding scenarios.

Of course one could take a calculated risk if it's known load and demand will never be extreme, or the brake system has proved itself under extreme demand by multiple users. I've seen a video of a bicyclist ride the Stelvio pass descent no hands, never touching his front or rear brake levers, but I have no faith I could do the same.

What sort of frame considerations does that 180mm rear rotor create, if any?

I suppose that if you were designing a frame for discs that it might not be any harder to include the ability to handle bigger disks later on if you needed it. Very hard to do later on if you change your mind!

If I guess the weight of the heaviest guy (the one who liked discs on the CX bike) then I guess we are talking about a total 115-120kg rider and bike package (about 250-260lb). This is at the limit of SRAM were designing the system for.

Dropouts face the wrong way (one pic looks like there's lawyer lips, but still)
Disc mount too small,it concentrates most of the stress in one small spot AND has a nice indentation put in the fork blade right where the stress is highest! At least they let you know exactly where your fork will fail.
There's a couple other things, but they have already been addressed in this thread.

The company either must not sell a whole lot of forks or the forks last because they are on fixed gears.

Jonny; I never stopped putting a rear brake bridge on frames in general, but have for a long time (as do many builders) included a threaded bit to the bottom side of the brake bridge to provide a nice 5mm fender mount point even for frame buyers never expected to need or want fenders. I basically see a well implemented brake bridge as an integral part of the seat stays from the structural element perspective. Also think a frame looks sort of goofy without a bridge (but that is more of a personal problem of mine).
/K

Seems to me that, since the brakes come with a separate adapter for 140mm vs. 160mm rotors, that it would be fairly simple to machine yet another adapter to accommodate a larger rotor without having to go to non-standard frame mounting points.

I've seen quite a few undrilled bridges on production bikes - not just track frames either.

"Car and motorcycle enthusiasts have been thinking about this for a long time and have gotten past the "the wheels will lock - how much more do you need?" question. The ability to bring the wheel right up to the edge of skidding/locking but not have it go past that............and to do this time after time and in all weather conditions is the real deal IMO."

I get it, living in the north we do it on ice half the year with 50 grand of truck, and kids in the back seat. That is car road condition. But I haven't really heard anyone say why a road racer would want this. If we are just saying bikes on roads, fine, I get that, it is already pretty common. But I thought this thread was about new tech coming out for road racing bikes. I am not questioning anyone's opinion in this, I just don't get the killer app on road bikes, because I don't know enough. I know why for clydes, why for rain, why for MTBs, and cross bikes, I just don't know what would justify taking on the extra weight on a road racing bike, or a particular category of them. I want to see that situation where a guy who races for a different brand so wants these brakes that he has them put on his bike and paints over the graphics.