Revisiting disc brakes
As some of you know from my past posts, I have Avid BB7 road discs on my tourer (Dawes Sardar). Last week I did a tour of the Yorkshire Dales in the UK, fully loaded with tent, mat, sleeping bag, etc.
However, because British Airways now only take bikes in a bag or hard case (and I didn't have the money to buy a hard case) I decided to take my backup tourer which is an old Specialized Hard Rock converted to a tourer with racks, Nashbar canti brakes, trekking bars and Schwalbe Marathons. Since my primary tourer is so hard to get over here in the States (Dawes Sardar) I just couldn't stand the thought of it getting dented (I should add that if I did more touring I would buy a hard case and the Sardar would have gone in a heartbeat).
Anyway, this tour has made me rethink my thoughts on disc brakes. Though I love my disc brakes, I've maintained they are only really nice things to have, but hardly that necessary and are low value given the quality of some canti/v-brakes and brake pads and the cost of discs. I'm now not so sure.
Given some of the hills I went down, I think on a very hilly tour with sharp grades and corners, I'd heartily recommend disc brakes. On quite a few descents I had to continually apply my brakes for prolonged times due to the grades and sharp corners -and this resulted quite often in my rims becoming very, very hot -certainly to the point where I couldn't touch them. It got to the stage where I stopped and let the rims cool off for fear of damaging the pads or blowing the tyre.
So I'm changing my stance on disc brakes a little -if you have a very hilly tour, go with discs, they are worth it! (though if you are on a relatively flat tour then traditional brake setups should be fine.)
Have a read of this test...the results are a few years old, but brakes are getting lighter and lighter so I doubt the results would be radically better today. Ultimately both disc and rim brakes will fail if overheated and the range of heat they can take before failing is similar.
Most people [myself included] that have toured in the mtns have done so with rim brakes and not had a major issue. Read CGOAB and check out reports from tours that were done in the mtns or in hilly areas - are people with rim brakes having loads of issues?
If you continually apply the brakes for prolonged times with discs you will damage the disc brake - quite possibly permanently. If you ride assuming discs are immune to overheating you'll have problems.
I have toured with discs and I think they make sense for some bike applications, but if I was building up a new touring bike it would use v-brakes like my LHT. Pretty much all my touring is in the mountains.
Well that makes interesting reading -but I can't say it corresponds to my experience (lx v-brakes and Nashbar cantis with Koolstop pads and Avid BB7 road discs). And I'd take a warped disc over a front blow out too! I think disc warping has to depend on the quality of the discs -much like automotive brakes.
What's really interesting is the brake fade -I didn't expect to see that, and I'd love to see more information on how the test was done. E.g. "The test simulated a long downhill ride, on which the brake was used to maintain a constant speed of about 25 km/h (15.6 mph). The brake power was kept constant until the temperature at the mounting bolt did not increase any further, at which point the power was increased in increments of 200 W". I'm not sure I understand this -why test based on the mounting bolt temperature? Obviously the mounting bolt for a rim vs. disc brake probably isn't equivalent, let alone different disc brake designs -I would have thought that time would have been a better measure -might not be understanding the test though, or the web page didn't explain it thoroughly. I think the description of the test raises other questions as well.
One interesting point of my tour: it wasn't so much the hills and severe gradients, but the fact the gradients were not sweeping or prolonged -sharp corners came very quickly. I couldn't apply the brakes sharpishly and then let off for a time, I had to continually apply the brakes to prevent overshooting a corner -it wasn't what I'd consider the usual mountain roads (at least in the States and Canada). It's not that my rim brakes failed -more the fact I'd guess my discs would have been better performers (but I readily accept that I do not have hard facts or data to back that up, just a feeling as to how my brakes have performed previously).
The heart of the question is can you dump more heat into disc brakes than you can into rim brakes? I agree this test is only part of the answer, but until we get more testing from objective sources it's what we have to go on and the answer seems to be no.
I also agree [as does the test] that a front blow out is more serious than a destroyed disc brake, but let's keep in mind if your disc brake will no longer work [ie. the plastic parts melting in a Avid BB7] you now have to ride your tour with one brake caliper and presumably you are still in the mtns so now you have to manage your braking heat load with one brake until you can get a replacement - that won't work for long. Kind of like winning the battle and losing the war.
I'm not slamming disc brakes....I have several sets and use them as well as v-brakes, but what I do think is really important is that we don't embrace an attitude that rim brakes don't work well and that disc brakes have no faults. In the case of this issue I think we can agree that you have to be careful how you brake and how you heat up your brakes when riding a heavily loaded bike in the mtns or hilly areas regardless of what type of brake you are using.
Most people that tour in remote mountainous areas are doing so with rim brakes and most people riding touring bikes are doing so with rim brakes. Just like everyone who mountain biked before discs did. They work and people are not suffering blow outs left, right and centre.
As you noted I would also love to see more testing done. I'll keep looking for it and I'll keep an open mind.
Last edited by vik; 09-26-08 at 10:06 AM.
I've toured in the Rockies and the Appalachians and found rim brakes quite adequate. I am convinced that technique is as much a factor as anything. I have descended many steep multi mile descents without the rims getting too hot to touch. I tend to apply the brakes fairly hard in bursts rather than continuously. If necessary I alternate between front and back brakes. Also if it gets too bad you can always stop to let them cool, although I have never needed to.
Originally Posted by Nigeyy
I have one good reason to favor disc brakes!
Vik, I think we mostly agree -even though I've got a bike with disc brakes, I certainly don't think I could be classified as a disc brake evangelist (I've posted quite a few times that I wouldn't recommend to buy them based on -at least what I think -is low value compared to traditional rim brakes). I definitely agree that you can't say discs are the best thing, nor can you do that with rim brakes either (too many variables). Both brake types of good quality offer some good braking.
Still, if I were to do my tour again with those sharp twisting descents, I'd want to reach for the touring bike with discs!
Oops sorry staehpj1, I should have been clearer -it's not that I think good rim brakes aren't good enough for mountain touring -just that for the riding I did it was very twisty so I couldn't do bursts of braking at all (which is my norm too) and the road was too steep to do alternate braking. It really was necessary to do continuous braking to prevent overshooting corners.
Originally Posted by staehpj1