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Road Disc Breaks(13 posts)

Road Disc BreaksFreerangerhino
Oct 4, 2002 6:04 AM
Has anyone out there seen anything on road disc breaks? I imagine that it could change road riding by leaps and bounds. Just think of the rims that could be built if there were no need for a heavy breaking surface. Also you could move the rotational weight closer to the hub. Rims would last forever and breaking would be much improved on big downhill runs.
Relatively limited,TJeanloz
Oct 4, 2002 6:45 AM
The application for road disc brakes are pretty limited. They do exist, however, particularly for Cyclo-cross applications. Rims could be lighter, but the overal system is going to be heavier than calipers, and functionally, they wouldn't really improve braking, except maybe in the rain.

That being said, Avid does make a system that will work. And amusingly, we had a JC Penny road bike in the shop that was probably 15 years old that had an original hydrolic disc brake system installed on it.
agree that it may be a relatively limited market...sprockets2
Oct 4, 2002 9:13 AM
but there will be some. Moreover, I think you need to spend time on a disc mountain bike vs. a rim brake version. Your comment that there will be little improvement in braking doesn't sound like the voice of long experience. "Maybe in the rain" is downright funny.
Read the post below,TJeanloz
Oct 4, 2002 9:34 AM
The weakest link in road bike braking is the contact patch of the rubber on the road. My experience with mountain bikes is that in dry conditions, disc brakes work marginally better than V-brakes, and in wet/muddy conditions, they work phenominally better. Maybe this experience has been unique to me. I also note that my caliper brakes aren't nearly as effective on wet rims as I believe a disc brake would be.

The most that you can slow down a wheel is to a full stop, which causes a skid. This can be accomplished in almost any conditions on a road bike with a caliper brake, and I don't see what the disc brake is going to improve- calipers have more than enough power. If caliper weakness were a problem, we would have switched to cantilevers or V-brakes on road bikes years ago.
OK, I see where you are coming from....sprockets2
Oct 7, 2002 9:01 AM
and you are right, if they were awful we would have changed. I have got to say, however, that there have been a couple of wet road and mountainous road descents that have made me wish I had my discs. These things don't come up often but they do come up.

Probably the biggest arguement against road discs is that the MTB environment is simply one that would be more likely to benefit from discs. It could be useful to a roadie, but much less commonly.

I have found that discs are superior to even XTR and the top Avid Arch model brakes. In some conditions-like the ideal conditions-the differences might not seem important. But add the real world of high-g braking, dust, grit, mud, and water and brother there ain't no comparison. I agree, as you note, that once its locked, that's it, so all the extra brake force in the world ain't gonna stop your skid. But I have been in lots of situations where neither brake was gonna lock up any time soon and I was wishing, with white knuckles, that I had discs.

Nobody should just take my opinion/experience on this. I think that if you search among any MTB media or online forum you will likely get the opinion that discs are generally regarded as superior in performance in all conditions to even best vbrakes. However, for the road, in the meantime,as you noted, if current tech was that bad...
downhill braking?filtersweep
Oct 4, 2002 6:59 AM
are you kidding?

Disc brakes are used on mtn bikes because use of brakes is much more of a technical feature of the "sport" than in road biking-

a road bikes tires are VERY different than a mtn bike's tires- there simply is not enough of a contact patch on a road bike to "improve" braking- ie: it is the weakest link- and no amount of technology can change that.
furthermore...sprockets2
Oct 4, 2002 9:09 AM
Mavic has a road disc set out, but I think more importantly, the new XTR disc brakes point the way toward light and effective discs that will take away the worry about weight for many roadies. I won't take the plunge for a while but I agree that the prospects for many riders is somewhat exciting. However, I am not looking forward to fork makers claiming their carbon forks are disc-ready. I am still not a big believer in carbon although I do ride on them.
furthermore...divve
Oct 4, 2002 3:39 PM
Just thought you'd like to know. The new 03 XTR disc set-up isn't any lighter than some of the current offerings by Magura and Formula + XTR 02 RapidFire shifters. 02 XTR RapidFires + Magura Marta SL or Formula B4 SL are respectively around 50 to 100gr lighter.
re: Road Disc BreaksLactate Junkie
Oct 4, 2002 10:45 AM
Here are a few things to consider:

1. Road bikes using disks will be heavier. The disk, hub, rim and (if you use a front disk) fork all have to be beefed up.
2. The fork is a big issue because having the braking force at the hub causes a lot more wind-up than if it is at the rim. I have seen some CX bikes with disks where the front tire hit the down tube because the fork pulled back so much under braking.
3. The rims will probably not be lighter as you will need to reinforce the spoke area to hold up to the increased tensions caused by the force on the disk.
4. Radially spoked wheels are out, because you need the tangential pattern, again to support the loads from the disk.

Most of this stuff can be engineered around, although there is going to be a weight penalty no matter what you do. Given the performance increase is going to be limited, it is probably going to keep disks out of general road use.

I think you might see them getting limited use from pro teams in the future for the down hill sections of mountainous road races, where the riders can take bike changes. In this case disks, maybe only on the back, may be of advantage because of the increased power (especially in the wet) and the reduction in rim heating and the problems that creates with glue failure and heat related blowouts—we will see.
there was a whole argument about this on the Cyclocross boardlonefrontranger
Oct 4, 2002 6:14 PM
and very recently too, I might add.

You can read the entire thread and all of our harebrained ideas about this topic here:

http://forums.consumerreview.com/crforum?viewall@@.efb7c41
re: Road Disc BreaksDougSloan
Oct 7, 2002 10:20 AM
All carbon rims could benefit from disc brakes, although the braking of carbon rims is getting better these days.

I was thinking, aren't disc brakes and caliper brakes really two versions of the same thing? Conventional brakes are really giant discs with the inner portions removed, a gap inside the discs (rims), and with mechanical instead of hydrolic actuation? Both of them essentially use a caliper to clamp down on a disc. Further, isn't there some benefit to having the disc as large as possible to gain more mechanical advantage? Would hydrolic rim brakes be ideal, if you can obtain enough travel? (been done, right?) Would the ultimate version of a disc brake be a rim caliper brake?

BTW, I found v-brakes with ceramic coated rims to be fantastic in the wet and mud on a mountain bike.

Doug
All Theoretical For Mepeter in NVA
Oct 7, 2002 1:24 PM
I am one of those posting on the Cross board favoring discs for cx bikes...but I have no basis for it! I have never tried, much less seen an actual road/cx with discs. I would love to here from someone who has.

I have been experiementing riding my road and cx bike with axial pros 23 off road to just compare cantis with calipers and am not sure what to conclude:
1. On dry level trails, its easier to control the bike with cantis, but I think that's because I brake from the hoods and can't squeeze hard enough with calipers.
2. Steep downhills much easier with cantis for the same reason.
3. On mud, no difference...go sideways.
4. Dry road-calipers feel much better with better modulation.

I doubt there are markets forces for road disc equipped bikes-but I remember the same argument about suspension for mtb in the late 80's.
Aluminum vs. steelSpoke Wrench
Oct 8, 2002 6:36 AM
I think that this is a variation of the tired old aluminum vs steel argument. To simply state disc brakes do this or that better is to overlook the fact that the various models of disc brakes have quite different performance characteristics.

I have a Formula disc brake on the rear wheel of my tandem. I think that it's only marginally adequate because it does not provide the stopping power of the linear pull brakes that I had previously. It also clearly does not have the ultimate stopping power of my two sons' Hayes hydraulic equipped mountain bikes. But stopping power is only part of the issue.

My tandem brake was designed to keep heat away from the rim on long downhills and to keep the brake from locking up due to thermal expansion of the brake fluid. I still think that it needs more work. Incidentally, Hayes says not to use their brakes on tandems.

The point is that we are living in an area of rapid product development. To say that steel frames ride this way or disc brakes perform that way is to deny the differences between the individual offerings. I think that these differences sometimes exceed the average differences between the product families. For example, the difference in weight between the heaviest and lightest steel bike frame would probably be greater than the weight difference between the average steel and average aluminum bike frame.