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Avid road/cross disc brakes?(13 posts)

Avid road/cross disc brakes?kenyee
Nov 26, 2002 7:37 AM

I didn't realize they made these. Are they relegated to cross bikes only? I'd assume you need beefed up forks and mount points for the disc brakes...
why do you want them?gnailuh
Nov 26, 2002 9:28 AM
what advantage would you get? they shed mud better... but weight a ton more... not only that, they add rotational weight. i personally don't think the stopping power is that necessary.
Oh no - here we go again...nmEager Beagle
Nov 26, 2002 9:29 AM
I'm just surprised they actually make them for the same reasonskenyee
Nov 26, 2002 12:20 PM
Only reason I can think of is if you do a lot of descents. Standard road brakes overheat the rim and you risk blowouts. The disc brakes won't. Disc brakes are used on tandems too.
re: Avid road/cross disc brakes?Trek Racer X
Nov 26, 2002 11:51 AM
For a road bike, there is no need for that much stopping power. MTB Downhill racers use Avids, with 8" rotors to stop their 50 lbs. bikes. That is why Cyclo-cross bikes use cantilever brakes, becuase too much stopping power will result in loss of traction and thus skidding out. The stopping power of a rim brake is amplified by the size of the wheel. A BMX wheel would require more stopping power, than a 700c wheel becuase it is smaller. Other than somewhat of a cool factor, disc brakes adds rotational and stationary weight.

re: Avid road/cross disc brakes?Lactate Junkie
Dec 2, 2002 4:52 PM
This whole "don't need, can't use that much braking power" thing has come up time and time again and is always wrong. The whole coefficient of adhesion argument is also spurious. More power equals more control--always. When Shimano introduced the dual pivot system (actually Altenberger in the 70s' but who's counting), Campy said "too much power, racers don't want it or need it—guess what—BS. When Shimano introduced V-brakes, everyone said, "who needs that much power, I can already skid my wheels"—again guess what—more power—good!! Guess what happened when disks came out for mountain bikes? You got it, "don't need all that power, I can already skid my wheels" – see the pattern. Ultimately, what is going to determine disk use on road bikes is weight. Right now, the brakes themselves add about 400g and you will need to beef up the fork and probably the rim to support the increased loads. The hubs are also heavier because they have to support the rotor, so the total weight damage is at least 2lbs, at the moment. Guess what, disk brakes will get lighter as will everything needed to run them. At some point, they are going to be very worth while and practical.
Discs on cross wheels?------old news.CharlesTT
Nov 26, 2002 10:32 PM
There have been disc brakes on cross bikes using tubular cross tires for a year and 1/2 now. It set a new standard for some racers. In about 2 years were going to be seeing mechanical discs on road bikes in grand tours. If you have had bicycling mag. for the past 4-5 months, there was an article. If you think about it, just a little. Well, all rim brake wheels must have a braking surface. This limits the design of the rim. In a road race or cross race, the additional stopping power, and all weather control will be advantages only. If you save weight by getting rid of the breaking surface on a wheel, a rotor and caliper would not be able to make up for that. In the article I read, the author says he will be allover the first DeRosa with disc tabs...... you know you will too.
how small can they make the rims?kenyee
Nov 27, 2002 7:11 AM
I thought a good portion of the braking surface was used to increase strength?
Did the article mention how much weight you could get rid of from the rim if it had no braking surface?
how small can they make the rims?JFST
Nov 28, 2002 6:53 AM
It wouldn't be too surprised if road specific disc brakes started to show up on road bikes. Discs are becoming the standard in all types of mountain bikes. Their weight and cost is approaching that of a rim brakes but with completely superior braking performance. Obviously the braking power of a mountain disc would cause skidding to happen very easily but I wouldn't be surprised if toned down versions with different pad compounds and smaller rotors and pads showed showed up.
Vote JFSTEager Beagle
Nov 28, 2002 8:05 AM
quite correct - in fact, if they are not commonplace in 5 years, I'll eat my spokes...
how small can they make the rims?Spoke Wrench
Nov 29, 2002 1:49 PM
Sun Rim produces a DS1-SC mountain bike rim with no brake surface that is advertised to weigh 400 grams.

They also produce a Sub IV mountain bike rim which has a brake surface that is advertised to weigh 390 grams.
Big Whoopgrzy
Dec 4, 2002 8:57 PM
400 g. for a MTB rim disc specific or not is no big deal. Mavic 517 (with braking surface) is advertised at 395 g. while the 317 Disc is at 395 g. Getting rid of the braking surface from the rim doesn't really save much weight at least on a MTB rim. The real problem is that if you make the thing too light it's not durable enough to be of any use. There is a big trend in MTB disc rims to actually get heavier, but that has more to do with riding style and hucking. Now your beloved Sun rims are pretty much crap - I just got through replacing a couple DS1-XC's for a buddy that didn't cut it AND they don't even make that rim anymore. It's been replaced by the DS2-XC - I hope it's new and improved. Could they come up with more aerodynamic and potentailly stronger sections if they were free from the constraints of having parallel sidewall? Absolutely. Maybe this would allow lower spoke counts without having such flimsy wheels.

So can they make a road bike rim that's lighter? Sure they've been able to do that for years and the problem has never really been with the braking surface, but rather the dang things aren't strong enough to survive hitting anything. Even if you were to cut 10% from the weight of the rim, which is significant from and engineering point of view, but still only 40 g., you more than make up for it when you replace the braking system with a disc system. Some will argue that the rotating weight has been reduce which is true, but at what cost? Look at the Mavic Cross Max disc vs. non disc wheelset - one has a braking surface and one does not yet there is no appreciable difference in rim weight even though they had the opportunity with the different extrusion sections.

What really has to happen, and maybe it's just a matter of time, but somone has to take the Avid Mechanical road caliper design and design a light weight version. A weight reduction of 25% though better materials and finite element analysis would make this braking system even more attractive. The street price on the caliper and rotor is only $80 - for twice that you should be able to get pretty exotic and svelt. It's a pretty smart design, works well, and it's simple to setup and maintain. The braking force exceeds many hydraulic systems that I've messed with and there's no fluid to screw with plus you can continue to use your Ergo/STI shifters.
how small can they make the rims?Lactate Junkie
Dec 2, 2002 4:41 PM
Actually, the rims will likely get heavier as you will need extra material to support the increased pull on the spokes under braking. Maybe not, it depends on how good engineers get at moving material from one part of the rim to another within the constraints of what you can do with an extrusion.