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Old 05-05-12, 06:59 AM   #1
TheReal Houdini
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V-brake vs. BB7 for long, loaded, fast descent.

I was disappointed to discover that I chewed nearly all the way through a set of v-brake pads on a single rainy descent off Skyline Drive in Shenandoah National Park. Furthermore, my stopping power subsequently went to crap, presumably due to glazing of the brake pads - after the descent, not during.

My Novara Safari is set up to run either v-brakes or discs.

I've read that disc brakes can overheat on long, fast road descents resulting in potentially catastrophic loss of stopping power. Can anyone confirm or deny this for Avid BB7s?

I've read that disc brake pads can glaze under similar conditions. Can anyone confirm or deny this for Avid BB7s?

Would disk break pads require substantially less frequent replacement than v-brake pads?

Thanks!
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Old 05-05-12, 08:38 AM   #2
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Quite controversial issue here in the forums, So I will try to remain impartial.

For V brakes, try some different pads first before you go through the expense of switching to disc brakes: Kool Stop salmon compound. See how those work for you.

Yes, disc brakes will also overheat on a long descent and you'll wear your pads quickly, too. You can minimize that with putting a larger rotor up front (e.g. 180mm), but the ones that come stock should work really well. You may have to play a liitle with that after a few tours. An advantage that many point out is that with disc brakes (besides amazing stopping power) you don't wear out your rims. It's usually easier and cheaper to change a rotor than an entire rim.
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Old 05-05-12, 08:56 AM   #3
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No one uses anything but friction for brakes. as you watch meteor showers
that is friction in action..
Rims on the bike, are very big disc brakes..
Toured for a few decades in summer on rim brakes,same pads fine at end of any trip
now have BB7 on my wet weather commuter.[160 on 20" wheels]
if there are worries, rim brake inserts, or disc spare pads in the bag take up little space .

technique matters. if you brake hard for a short period of time then let go ,
heat will not build up, like holding the brakes on and constantly dragging them.

Last edited by fietsbob; 05-05-12 at 09:18 AM.
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Old 05-05-12, 09:00 AM   #4
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Compromise. Disc on back, V on front. Less weight and fiddle factor than two disc, stopping power when needed. Switch to Kool pads.
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Old 05-05-12, 09:02 AM   #5
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I have bikes with v-brakes, Avid BB7's, and hydraulic disk brakes. As far as stopping power and modulation, the hydraulics are the best. However, they are on my mtn bike, and I don't think I'd want them on a touring bike because of the difficulty with bleading the brakes and the potential for a damage line. The BB7's are great brakes, never had any issues coming down steep roads, lots of power, and simple to set up and adjust. For general riding v-brakes have served me well, but after having the power of disk brakes I prefer them.

I'd try different pads, I use Kool Stop, and find them far better then the crap that comes with most bikes as standard equipment.
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Old 05-05-12, 09:46 AM   #6
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Quote:
Originally Posted by TheReal Houdini View Post
I've read that disc brakes can overheat on long, fast road descents resulting in potentially catastrophic loss of stopping power. Can anyone confirm or deny this for Avid BB7s?
The longest descents I've done are probably in the 3-4 mile range with an average grade of -7 or -8%. I've never had a problem with overheating on my BB7-equipped touring bike. On long descents, I do concentrate on proper braking technique (alternate front and back brakes, brake hard when needed then release pressure rather than having brakes constantly engaged, etc).

Quote:
I've read that disc brake pads can glaze under similar conditions. Can anyone confirm or deny this for Avid BB7s?
I suspect that it's possible to get any brake pad to glaze if you treat it poorly enough. I also suspect that stock brake pads are optimized for low price rather than best performance; there may be replacement pads that work better. That said, I haven't had a problem with glazing on my BB7s.
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Old 05-05-12, 11:44 AM   #7
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Originally Posted by sstorkel View Post
On long descents, I do concentrate on proper braking technique (alternate front and back brakes, brake hard when needed then release pressure rather than having brakes constantly engaged, etc).
I suspect that it's possible to get any brake pad to glaze if you treat it poorly enough. I also suspect that stock brake pads are optimized for low price rather than best performance; there may be replacement pads that work better. That said, I haven't had a problem with glazing on my BB7s.
all very good points, especially about not having brakes constantly engaged. This is common behaviour with some people and really does cause more problems that alternating and hard applications when needed.

also, as someone who has also toured loaded in very mountainous areas (and has experienced brake fading and/or hand tiredness requiring a stop to let things cool down) I do question that you went through a "set of pads" on one descent. One possibility is that you never clean your rims or pads and lots of abrasive has accumulated over time (or did in that section) . Even if it did accumulate during that descent, it doesnt make sense to have gone through that much pad material in such a short time--again, not an accusation but from my experience going down hills with a load.

do try diff braking techniques and you will see that brake fade will be less of an issue.
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Old 05-05-12, 12:13 PM   #8
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Brake hard, one rim at a time, and keep your speed up. Don't feather the brakes. Let the bike run as much as you can. You'll need both brakes before hairpins. When lever pressure to get the same effect increases, stop and let your pads and rims cool. This procedure works for 350+ lb. tandems. It will work for you. On a mass tandem descent of Mt. Ventoux, the only bikes that had big brake problems were running discs. Rim and drum brake bikes did fine. This probably can be laid to overconfidence on the part of the disc-equipped teams.

However that may be, you won't like it if you warp a rotor or melt all the plastic parts off your calipers in the middle of a tour. You also won't like it if you blow a tire off a rim. Historically, the only tires known to have been blown off tandem rims by heat were wire bead, FWIW. I always carry two sets of spare pads for rim brakes. They're small and light - ditch the packaging, bag them with their pins. I always carry a mini Leatherman, mostly for this purpose. Yes, Koolstop salmon, KS-LPVBSA for V-brakes. Google, they're rare to find on the shelf.

If you have an alcohol stove, wipe the rims with alcohol in the morning before a section with a big descent, or every morning. If you don't, consider carrying a small bottle of alcohol for this purpose. This makes a very big difference both in braking and in the life of your rims.

As all that may be, your rims will last a lot longer if you run discs. OTOH, they're a heavy addition and you already have rims. It can be argued 5 ways from Sunday.
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Old 05-05-12, 02:12 PM   #9
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Yeah, modulation is the key for long down hills. Never had any trouble doing that. Have stopped occasionally to let rims cool. Pad wear was never a problem. Longest decent was 8 miles, 5%.
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Old 05-05-12, 04:58 PM   #10
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This guy here talks about his encounter with brake fade on discs. 180-200mm rotors should not have the same issues, but the author of the article thinks discs on road bikes will be smaller.

It doesn't sound to me like discs would help much on massive descents, at least not enough to justify the upgrade costs. If the descent wrecked a pair of v-brake pads, it'd probably wreck disc pads as well. I'd go with discs if you have some other compelling reason, e.g. cycling in bad conditions.
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Old 05-05-12, 05:00 PM   #11
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Quote:
Originally Posted by TheReal Houdini View Post
...My Novara Safari is set up to run either v-brakes or discs.

I've read that disc brakes can overheat on long, fast road descents resulting in potentially catastrophic loss of stopping power. Can anyone confirm or deny this for Avid BB7s?

I've read that disc brake pads can glaze under similar conditions. Can anyone confirm or deny this for Avid BB7s?

Would disk break pads require substantially less frequent replacement than v-brake pads?
Go ahead and take the plunge to BB7s (road or mtb version depending on your lever type/budget), you probably will be glad you did.

I've never had my BB7 discs overheat or glaze. The only thing bad that's happened to my BB7s was a rotor got bent, when something was moved in garage into bike leaning against wall. I was able to straighten the disc with an adjustable wrench while still mounted to hub. I think the pads do wear slower on BB7s than Avid SD7s (rim brakes I used for many miles), so replacement is less frequent and easier, since it's not necessary to carefully reposition or toe-in disc pads - they just drop into place.
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Old 05-05-12, 05:09 PM   #12
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My take on Disc brakes is simple. If you ride in the rain often, use disc brakes. If your riding is in dry weather 90% of the time, disc brakes may not offer enough of an advantage.

Portland, OR or Seattle: Disc brakes
Tucson: Rim brakes
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Old 05-05-12, 05:39 PM   #13
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That's a pretty good "rule", Barrettscv.

I'd modify slightly and say "or, if you roll down mountains with a heavy (rider+gear) load".

I'm sure there's a lot of fair-weather flatlander bicyclists who are completely puzzled by some folks seeming obsession with disc brakes.
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Old 05-05-12, 06:06 PM   #14
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I have a 2007 REI Safari. I changed over to BB-7s. I sometimes have my BoB trailer on this bike. I can say I have noticed improved braking with discs going downhill. I keep my loads on the light side and my body weight also low.
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Old 05-05-12, 06:39 PM   #15
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Originally Posted by seeker333 View Post

I'm sure there's a lot of fair-weather flatlander bicyclists who are completely puzzled by some folks seeming obsession with disc brakes.
I have two bikes that have both Disc tabs and Canti bosses. I have never felt the need to install a system that is;

Heavier
More Costly
Requires special hubs and a very strong wheel build
Requires an extra stiff fork to avoid twisting forces.

Only in winter do I think I might be missing something. But then, I have never had a situation where the rim brakes failed to do it's job well.

If I lived in a rainy region with hills, I would install discs.
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Old 05-05-12, 06:40 PM   #16
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Thanks, especially to those with BB7s. A few notes:

1. In retrospect, it was probably only half of the brake pads, not the whole thing, but still a lot.
2. My braking technique is good. The Houdini moniker was actually bestowed by fellow cyclists for on-bike behavior. However, it was raining and the reduced visibility and traction for both me and the motorists inspired me to brake harder and more frequently than I otherwise would have.
3. If I recall, the catastrophic failure of disc brakes on long descents was actually due to boiling of the hydraulic fluid - not an issue with bb7s.
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Old 05-05-12, 06:58 PM   #17
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rim brakes, loaded bike. no worries.

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Old 05-05-12, 09:21 PM   #18
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If you search for something like disc brakes on a touring bike you will read pages and pages of back and forth over which is better for a touring bikes. When it really comes down to it though, both systems have proven themselves and each has its minor quirks but when set up properly they both can work quite well in any situation.
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Old 05-05-12, 10:09 PM   #19
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rim brakes, loaded bike. no worries.
Iron Horse trail descent? Beautiful country. Looks like you're descending into western WA, reverse of the usual. That is pretty fast for that surface.
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Old 05-05-12, 10:11 PM   #20
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Originally Posted by TheReal Houdini View Post
Thanks, especially to those with BB7s. A few notes:

1. In retrospect, it was probably only half of the brake pads, not the whole thing, but still a lot.
2. My braking technique is good. The Houdini moniker was actually bestowed by fellow cyclists for on-bike behavior. However, it was raining and the reduced visibility and traction for both me and the motorists inspired me to brake harder and more frequently than I otherwise would have.
3. If I recall, the catastrophic failure of disc brakes on long descents was actually due to boiling of the hydraulic fluid - not an issue with bb7s.
My anecdote was with BB7s. The plastic parts simply melted, which impaired the functioning of the brakes. Not the usual thing, though.
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Old 05-05-12, 11:01 PM   #21
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I prefer disc brakes on any bike I own. Yes, I am biased, I just wanted to state that up front.

As for Avid BB7s, I don't see how cable actuated brakes would overheat. The big issue with disc brakes theoretically overheating is that the brake fluid can get too hot causing brake fade, much like in a very aggressively driven motor vehicle. With the cable actuated BB7, there is no fluid to overheat, so it shouldn't be a problem.

I don't like the Avid hydros (Juicy line specifically). I'd steer clear of them. If you go with hydros, I have found the Hayes 9s to be virtually maintenance free in roughly 5,000 miles of commuting/utility/mountain biking. Given the choice between V brakes and BB7s, I'd choose BB7s. Between BB7s and other disc brakes, I'd choose Hayes 9s.

Last edited by hopperja; 05-05-12 at 11:05 PM.
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Old 05-05-12, 11:08 PM   #22
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Compromise. Disc on back, V on front. Less weight and fiddle factor than two disc, stopping power when needed. Switch to Kool pads.
I don't get your suggestions. Since most stopping power comes from the front brake, if you were only going to buy one new brake, why not put a disc on the front?
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Old 05-06-12, 12:21 AM   #23
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If you use the rear as a drag brake, its some what like a typical tandem use.
in a similar situation..

Or,
Door #3 Magura HS 33 .. the hydraulic rim brake. V brake boss mounted..
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Old 05-06-12, 01:13 AM   #24
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A couple of people have mentioned rim wear.

Most of my rides are flat, but there have been a couple of long descents, like one from 3900m to 1500 m, but my commuter has almost 17,000 km on the front wheel, and I can still see the front wear indicator....

Where I ride has a lot of grit on the road, so my bike is often covered with fine to coarse sand.

z
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Old 05-06-12, 05:14 AM   #25
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Originally Posted by TheReal Houdini View Post
If I recall, the catastrophic failure of disc brakes on long descents was actually due to boiling of the hydraulic fluid - not an issue with bb7s.
The brake pads can also glaze.

In the article I linked, the author talks to several manufacturers; mechanical vs hydraulic for discs makes no difference for brake fade. Conditions hot enough to boil the hydraulic fluid would just melt other components in the brakes.

I don't think discs offer any real advantage for descents like this.
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