dwightonabike

I am going to buy a touring bike, and I am worried that disc brakes will put too much stress on my spokes. Me and my loaded bike will weigh over 300 lbs, and although disc brakes work better in the rain, I do not want to deal with excessive broken spokes. Does anyone have any experience with this? Also, do disc brakes interfere with mounting racks?

cyccommute 

Disc brakes are sexy - and expensive. That's about all they have going for them. I have a mountain bike with discs but I really don't see it as stopping that much better than a bike equiped with v-brakes or properly setup cantilevers. I also have a touring bike with cantilevers (Avid Shorty 4) and carry a load right at what you carry. I do mountainous tours and have never had the brakes fail to stop me. Even in the rain they perform well enough to stop me.

Canti's work great. No need for anything more, really. Just learn how to set them up properly. Sheldon Brown, who else , tells you how.

gregw

I don't know too much about disc brakes, although they seem to be getting spec'd on a lot more bikes. I was dissatisfied with the cantilever brakes that came on my Cannondale and after lots of research I switched to Shimano XT linear pull V-brakes (also coolstop pads). This set-up works better than any kind of brake I have used in the past, very powerful, even on the low setting and very smooth. Very easy and precise adjustment, along with even pad wear. (my loaded rig with me on it is about 290lbs)
In the end the power comes from the leverage created by the moment arm of the brake. On all brakes that I have seen, v-brakes have a longer moment arm and therefore greater braking power. V-brakes and cantilever brakes work the very same way, just the lever arm is in a different position, by pulling across the top on the v brake they can use a longer lever. If cantilever brakes used the same length lever on each side they would stick out too much and always be bumping things.
Both v-brakes and cantilever brakes are essentially disc brakes with the rim being the braking surface disc. So you have a "disc" brake with a 26" or 700cm disc in Lieu of about 8"-12" used on the typical disc brake. Again much more leverage, obviously disc brakes make-up for this in other ways but the physics won't go away.
Hope this helps.

cyccommute 

The leverage advantage of V-brakes are not that much greater than a properly adjusted cantilever. The key is the adjustment.

The reason I'd suggest a cantilever over a v-brake is that the cantilever can be used with most any road bike lever without modification. Linear brakes require a special lever which, if you have barend shifters isn't a problem. You can just replace the lever. But, if the bike is equiped with STI, an adapter has to be used and the adapter causes its own set of problems. Or you have to replace the whole lever assembly with a barend shifter. This makes a $70 brake job into a $300 brake job pretty quickly.

dwightonabike

Lever vs. cantilever brakes aside, lots of new "touring" bikes are coming with disc brakes. I have heard that with disc brakes, the stopping force must be transmitted from the hub, through the spokes to the rim and wheel, creating lots of tourqe. I've heard that this is hard on spokes for touring, especially for big guys. Anyone else heard this?

gregw

I checked Sheldon Brown's article on disc brakes and he does not mention anything about there being a spoke issue. quotes below;

Hydraulic
While most bicycle brakes are operated by Bowden cables, some high-end brakes, most notably Magura, use hydraulic lines instead. Hydraulic brakes are costly, but work very well indeed. In particular, hydraulics on the rear avoid the problems associated with the loooong rear cable.
To mechanics unfamiliar with them they appear a bit daunting at first, but they're actually quite easy to work on."


Cantilever (direct-pull)
"The newest thing in cantilevers is the "direct-pull" cantilever. The best known version of this is the Shimano "V-Brake" ®. These are an elegantly simple design. The mechanical advantige is fixed, high, and doesn't significantly vary over the course of the stroke.
Because the mechanical advantage of direct-pull cantilevers is so high, they require special brake levers with reduced mechanical advantage (the levers pull twice as much cable, half as hard.) Although the necessity for special brake levers is unfortunate, it has the happy side effect that the cable tension is cut in half, which reduces the effect of cable "stretch" (a significant concern on the rear brake of a tandem, due to the long cable.)

For tandems with upright handlebars, direct-pull cantilevers are definitely the best choice.

Unfortunately, there is only one model of brake lever for drop handlebars that works with direct-pull cantilevers, the Dia Compe 287-V. This is a fine choice if you have barcon shifters, but won't help you if you prefer integrated brake/shifters such as Campagnolo Ergo or Shimano STI.

There are aftermarket devices to change the mechanical advantage at the cantilever by the use of an eccentric pulley, and these are sometimes a good solution for rear brakes, especially on smaller frames where there may not be sufficient clearance above the rear cantilever for optimal adjustment of a conventional cantilever. See my cantilever articles for details on this.

Some conventional cantilevers can be converted into direct-pull operation, again a good choice for rear brakes. See my cantilever articles for details on this.



Other google searches showed nothing either.

cyccommute 

I keep my eye on the touring bike market and I can't think of a single model that has discs. That's real touring bikes, not the cross bikes/urban bikes that are being sold as "touring" bikes. The disc equiped bikes I've seen don't have the proper geometry nor the proper braze-ons to qualify them as bikes for loaded touring. Trek, Cannondale, Fuji, Surly, etc don't use discs on any of their touring bikes. Discs add a lot of expense and complexity without adding durability and ease of repair.

I have not heard of any problems with breaking spokes due to torque. A properly built wheel should be able to handle that kind of stress. That being said, the other problems I can see with a disc is that the front wheel - the strongest one - is now dished to for the disc. This weakens the wheel. The rear wheel is also made weaker by the increased angle of the spokes leaving the wheel, making the wheel less strong laterally.

There have been some people saying that disc and wheels with quick releases on the front wheel are not a good thing. Vector analysis of the forces involved indicate that the quick release can be loosen and come open. It's highly contested by some and just as strongly defended by others.

If you want to read about it go here.

Michel Gagnon

Disc brakes vs canti or v-brakes: they are about the same in dry weather. The only advantages of disc brakes are that they behave the same way when wet and when (if) you ride in muddy terrain, you won't gouge your rims. But as you said, there are significant issues with rack positioning vs disc brakes.

I would suggest you won't have any problems with rim brakes. For better all-weather braking, replace the stock pads with Kool stop Salmon pads (about $10). Just to comfort you, tandem and even triplet owners rely on rim brakes to stop their rigs. Some add a third drum brake, but that's not to stop faster but rather to prevent brake overheating on long descents (i.e. more than 3-4 km).

amaferanga

The other obvious advantage with disc brakes are they don't wear your rims out. Typically a hub can see off 2 or 3 rims. With discs the rims will last longer. Also on long steep descents on rough roads (where you just can't go fast) in a hot climate you don't need to worry about overheating rims.

For touring (especially if you're off to remoter parts) then IMO the best option is cable discs. I've got an avid BB7 on the front of my bike that is fantastic and I suspect gives braking comparable to hydraulics. On the back I have a v-brake for two reasons - firstly, most of the braking is done with the front and secondly because it's more of a hassle fitting a rear rack round a disc on the back (I've got an OMM Sherpa on the front).

Excessive broken spokes will not be a problem with suitable, well-built wheels with even spoke tension.

Redbeard

I wonder where you picked up the idea of a spoke issue with disk brakes. Has somebody done some research, or is it just a claim? (Is there a salesman involved? That's often the source of urban legends!)

The drive torque is transmitted from the hub to the rim via the spokes. I would expect that, as you stand in the pedals on a loaded touring rig you would put much more stress on the spokes than a disk brake would. I would agree that it all depends on a well-built and well-maintained wheel.

SansCar

whether discs on a touring bike are necessary or not...the reality is that this situation does exist. Fortunately there are several options for fitting racks. I would recommend Old Man Mountain ...they're not the only solution out there but they're proven and high quality.

good luck.

dwightonabike

Thanks for all the advice. I think I have settled on the Surly LHT, so no disc brake issue. Now all that's left is to save up the $$$!