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Recreational Cyclocross and Gravelbiking This has to be the most physically intense sport ever invented. It's high speed bicycle racing on a short off road course or riding the off pavement rides on gravel like :The Dirty Kanza". We also have a dedicated Racing forum for the Cyclocross Hard Core Racers.

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Old 12-06-05, 05:22 PM   #1
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Disc brakes - benefits / detriments?

Aside from being further from the mud, are disc brakes really that useful? On most bikes, I can lock the brakes anyway.
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Old 12-06-05, 06:25 PM   #2
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it's not the power, it's the modulation. fine control is much better with disc. plus the near imperviousness to wet weather.

but they ain't "legal."
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Old 12-06-05, 06:40 PM   #3
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I would say they would be super useful for cross, mostly because of the mud thing. There are two types of cantilever brakes, the ones that are lower profile (don't stick out as much) and have less rim clearance in return for more braking power (but still nowhere near what you get with caliper brakes or discs) and the wide ones that give more rim clearance. I have the low profile ones, and they don't have that much power, and the low rim clearance means that if you are riding in mud (which is just about every cross race, at least in the north west where I am) you get a lot of rubbing on the rim. This may not actually sap that much power, but it sure is demoralizing to hear. With disc brakes you would not have this, you would have way better braking power, and you would also not experience any braking chatter that seems pretty common with cantilever brake setups.
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Old 12-06-05, 08:15 PM   #4
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Um, where do you get the idea that canti brakes aren't as powerful as calipers? When cantilever brakes first began to come into common use, they were rather considerably more powerful than many calipers. The gap has basically been closed, with modern dual-pivot caliper brakes and cantilevers being roughly equal in terms of braking power, these days, but cantilevers have an established reputation for better braking than calipers, and for good reason, despite the decreasing relevance of this reputation. The gap in braking power between discs and rim brakes is really not particularly relevant, however, as ALL modern rim brakes, when properly set up, are perfectly capable of locking either wheel. The arguments for disc brakes that make the most sense to me are that the modulation is better (something that I've never had proved to my satisfaction, but it could be so, and I haven't used discs), and that they are less likely to be affected by mud and poor weather than rim brakes. Since discs are not race legal, these are presumably the primary reasons, along with tradition, that cantis remain the most popular kind of brakes on cross bikes.

EDIT: Low-profile cantis do not have superior power compared to wide-profile cantis, which in fact exhibit superior performance in almost every way. The wide arms grant them better mechanical advantage, and the mechanical advantage does not change as much as it does on low-profile cantis as they move closer to the rim. The wides are generally easier to set up, as well. Low-profile cantilever brakes came into being primarily because of heel-strike issues on smaller MTB frames, not through any particular virtue of performance. The design of wide-profile brakes is simply better, and it's a shame that they are so hard to find these days.

Last edited by grolby; 12-06-05 at 08:21 PM.
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Old 12-07-05, 08:31 AM   #5
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Disadvantages to rim brakes:

1) They're too light.
2) They're too inexpensive.
3) They're too reliable.
4) They might take one revolution to wipe the rims clean before they start working. That's almost a second at slow speed.

Advantages of Disk Brakes:

1) They have a lot of added complications.
2) They have a lot of really good weight.
3) They always drag on the disk and add some additional drag so that you can build your leg muscles faster.
4) They are expensive.
5) You need special forks and frame to mount them or add some nice heavy brackets.
6) They can take a full revolution to wipe the disk clean before they start working - this might be a full second at slow speeds.
7) They are all non-standard so finding parts is always a fun adventure.

Seems to me that disk brakes pass all of the OCP requirements with flying colors.
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Old 12-07-05, 08:39 AM   #6
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Originally Posted by grolby
EDIT: Low-profile cantis do not have superior power compared to wide-profile cantis, which in fact exhibit superior performance in almost every way. The wide arms grant them better mechanical advantage, and the mechanical advantage does not change as much as it does on low-profile cantis as they move closer to the rim. The wides are generally easier to set up, as well. Low-profile cantilever brakes came into being primarily because of heel-strike issues on smaller MTB frames, not through any particular virtue of performance. The design of wide-profile brakes is simply better, and it's a shame that they are so hard to find these days.
Bzzzt! You just lost your mechanical engineering license.

The lever pull is the limiting factor. Most people might have noticed that levers are essentially all the same. There is a small difference in the leverage of "standard" drop bar levers and DiaComps V-brake levers but not a lot - in fact I believe the DiaComps still have a little more advantage than flat bar levers and hence a bit less pull.

The RATIOS of the wide cantilevers and the narrow cantilevers necessarily have to be nearly identical in order to move the pads about the same distances. It is true that the narrow cantilevers move in a tighter arc and hence have a greater change in lever pressure than wide ones but the difference is small.

As far as I can make out, the entire reason to have wide cantilevers is so that they can hang up on everything.
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Old 12-07-05, 08:52 AM   #7
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Whats the reason we havent seen Disc on roadbikes? Weight? Cost?
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Old 12-07-05, 08:59 AM   #8
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Whats the reason we havent seen Disc on roadbikes? Weight? Cost?
You don't really need that kind of power on a really light road bike. Calipers are more than adequate. I can easily endo or skid on my roadie if I want to (I never do, mind!) and there is plenty of modulation from the STIs.

The added detractions of weight and cost are further nails in the coffin as far as I can tell.
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Old 12-07-05, 10:22 AM   #9
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Seems to me that disk brakes pass all of the OCP requirements with flying colors.
That's pretty funny. I'm sure if the OCP sees me posting on the CX board, my days are numbered. All that mud covering my jersey.
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Old 12-07-05, 02:37 PM   #10
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Originally Posted by cyclintom
<stuff>
geez, cranky today? i agree with a lot of what you said, though. but:

1. discs are cheaper to replace than rims when the mud and gunk destroys them.
2. plain water is different from mud - i've had pad "float" and a loss of braking power in wet, clean conditions.
3. if your pads are rubbing, they aren't set up correctly.
4. weight? i just don't get this obsession with grams. maybe it's me. a good pair of canti's (Spooky) -sans pads - weigh like 150 grams or so. add another 90 g or so for pads (Koolstop). Avid's road discs weigh around 720 g complete. so that's about a pound difference. if i leave one of my watter bottles empty, i've just gained that back. heck, i could stand to lose 15 - 20 myself.

sure, for the ultimate upper echelon of racers, there is no reason to use them. those guys would actually notice a pound off the bike. that said, if the brakes themselves were legal, it probably wouldn't be too hard to build a 15 lb disc-brake bike.


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Originally Posted by shokhead
Whats the reason we havent seen Disc on roadbikes? Weight? Cost?
You don't really need that kind of power on a really light road bike. Calipers are more than adequate. I can easily endo or skid on my roadie if I want to (I never do, mind!) and there is plenty of modulation from the STIs.

The added detractions of weight and cost are further nails in the coffin as far as I can tell.
true, you don't need the power on your average road bike. i'm going to be building a 'cross bike for a wet-weather and town bike. it will be disc - not for the power, but for the all season stopping.
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Old 12-07-05, 07:46 PM   #11
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Bzzzt! You just lost your mechanical engineering license.

The lever pull is the limiting factor. Most people might have noticed that levers are essentially all the same. There is a small difference in the leverage of "standard" drop bar levers and DiaComps V-brake levers but not a lot - in fact I believe the DiaComps still have a little more advantage than flat bar levers and hence a bit less pull.

The RATIOS of the wide cantilevers and the narrow cantilevers necessarily have to be nearly identical in order to move the pads about the same distances. It is true that the narrow cantilevers move in a tighter arc and hence have a greater change in lever pressure than wide ones but the difference is small.

As far as I can make out, the entire reason to have wide cantilevers is so that they can hang up on everything.
Good thing I'm not a mechanical engineer, then . Anyway, my understanding was that wider arms gave greater force to the squeezing action of the brakes, but I'm willing to be wrong. I most certainly did find the braking of my bike to be best when I had it set up with a set of wide-profile Shimano XTs from back in the day. It's a dreadful tragedy that I had to get rid of them, due to fit and cable friction issues. The brakes I have now are certainly good enough, but I was greatly impressed by the power of those wide-profile cantis - the Tektro cantis I'm running just don't have as nice a response. It may be that the change in mechanical advantage is more significant than you suppose. I don't know.

In any case, the lever is certainly a significant factor. I haven't compared the Dia-Compe 287-V levers to my normal aero levers in terms of cable pull, since my bicycle turned out to be unable to fit v-brakes. Unless you are referring to flatbar v-brake levers, though, it would have to be dead wrong that they would have more mechanical advantage, since v-brake levers have to pull something like twice as much cable to make up for the high mechanical advantage of v-brakes. If you're referring to flatbar v-brake levers, than that makes sense, since aero levers have a pretty high mechanical advantage simply by nature of their design.

I consider the lack of adoption of v-brakes in cyclocross racing to be a more interesting question than disc brakes anyway, though I think it can be pretty easily explained by two things:

1. No one makes a brifter that can pull enough cable
2. Cantis are more than sufficient

Which of course leads to the question: if you could mount discs, would you? I certainly would on an all-weather commuting bike, but a cyclocross bike? If I raced cyclocross, anyway, and they were legal, I doubt that I would bother.
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Old 12-08-05, 12:35 AM   #12
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Um, where do you get the idea that canti brakes aren't as powerful as calipers?
Um, from the fact that after primarily riding my cross bike during the fall, when I take my road bike out for a spin I am amazed at the braking power.

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EDIT: Low-profile cantis do not have superior power compared to wide-profile cantis, which in fact exhibit superior performance in almost every way. The wide arms grant them better mechanical advantage, and the mechanical advantage does not change as much as it does on low-profile cantis as they move closer to the rim. The wides are generally easier to set up, as well. Low-profile cantilever brakes came into being primarily because of heel-strike issues on smaller MTB frames, not through any particular virtue of performance. The design of wide-profile brakes is simply better, and it's a shame that they are so hard to find these days.
Read this: http://www.velonews.com/tech/report/...es/9054.0.html
Either you don't know what you are talking about, or the person who wrote that article for velonews likes making stuff up. I'm going to bet it's the former.
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Old 12-08-05, 01:57 AM   #13
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Um, from the fact that after primarily riding my cross bike during the fall, when I take my road bike out for a spin I am amazed at the braking power.
Well, either your cross bike is poorly set up, or you ride it in conditions (rain, mud, etc etc) that degrade braking, or something else is wrong. You might also have forgotten that your road bike has a lighter frame and wheels, and may be conflating better modulation (which calipers generally have) with better power. The limiting factor on ALL brakes is the lever, as cyclintom says - you should be able to lock the brakes on BOTH bicycles. Given absolute braking capability, though, all factors being equal, my money is on the cantilevers (although dual-pivot calipers are probably pretty much on the same level).


Quote:
Read this: http://www.velonews.com/tech/report/...es/9054.0.html
Either you don't know what you are talking about, or the person who wrote that article for velonews likes making stuff up. I'm going to bet it's the former.
Techy, hey? I said that I made a mistake. I still don't see any reason to believe, based on my experience, that low-profile brakes are MORE powerful, and I certainly preferred the wides that I was running. Additionally, the increased change in MA over the lever travel is a real issue, in my book.

I don't have a lot invested in this. No need to get so mean about it. Would you prefer that I withdraw all comments about brakes, ever? I can certainly do so, since I seem to have gotten a few things wrong, here. I may be an ignorant, prejudiced doofus when it comes to my brakes, but I am certainly not stupid.
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Old 12-08-05, 08:29 AM   #14
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2. Cantis are more than sufficient
DING! DING! DING! We have a winner!

V-brakes trade distance for leverage. The ONLY advantage of this to the RIDER is that you can brake too hard with only two fingers without thinking about it.

The disadvantage to the rider is that you can brake too much in the monentary panic when you grab the brake levers with all your fingers. In the dirt this usually doesn't have a high price because the front tire usually skids before the bike rolls over the front wheel. On high traction surfaces though it can have some pretty dire consequences.

Why V-brakes then? Well the brakes become entirely self contained. That is the ONLY additional brackets necessary to use V-brakes are the Cantilever bosses. No cable brackets are necessary.

You have essentially the same problem with disk brakes. Since cantilevers brakes, both long arm and short, already have sufficient power to lock the front wheel you have to wonder exactly what goes through people's heads when they buy them.

One person raved about "modulation". Now I hate to point this out, but the reason that disk brakes were avoided for so long on road racing motorcycles was because they didn't "modulate" well. We had 4-leading shoe drum brakes so huge that the spokes were only a couple of inches long!

Another person claimed that if your disk pads were dragging that your brakes were incorrectly adjusted. Well, DUHHHH - exactly HOW do you suppose that loose brake pads "retract"? The caliper has to rattle back and forth a bit to KNOCK the pads back into the caliper far enough so that they don't drag. Looking at all of the fancy mounting hardware used to mount disk brakes you'll note that everything is pretty solid these days. Meaning that neither the caliper nor the disk can rattle back and forth and so the pads drag all the time.

As I've noted in several group discussions - what APPEARS to be tiny inconsequencial sources of drag add up over a long ride to be a trememdous work load.

Now let's discuss disk brakes even further since it is a completely brain dead idea to begin with.

Rim brakes are situated nearest the actual loads. One side of the brake is attached to the frame and the other drags on the rim very near the road surface.

Disks are attached to the hub and are much smaller diameter and must operate to slow the wheel through the spokes. Anyone else notice that you are going from direct loading to indirect loading here?

The long and the short of it is that disk brakes on bicycles (which already have the most superior disk already) is something that is little more than a marketing man's dream. It's a device that NEVER needed to be included on a bicycle.

Last edited by cyclintom; 12-08-05 at 08:36 AM.
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Old 12-08-05, 09:14 AM   #15
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You don't really need that kind of power on a really light road bike. Calipers are more than adequate. I can easily endo or skid on my roadie if I want to (I never do, mind!) and there is plenty of modulation from the STIs.

The added detractions of weight and cost are further nails in the coffin as far as I can tell.
I didnt think you could have to good of brakes.
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Old 12-08-05, 02:08 PM   #16
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Another person claimed that if your disk pads were dragging that your brakes were incorrectly adjusted. Well, DUHHHH - exactly HOW do you suppose that loose brake pads "retract"? The caliper has to rattle back and forth a bit to KNOCK the pads back into the caliper far enough so that they don't drag. Looking at all of the fancy mounting hardware used to mount disk brakes you'll note that everything is pretty solid these days. Meaning that neither the caliper nor the disk can rattle back and forth and so the pads drag all the time.

As I've noted in several group discussions - what APPEARS to be tiny inconsequencial sources of drag add up over a long ride to be a trememdous work load.
Well my friend, it appears that you have never owned or ridden a bike with disc brakes. The most common disc brake used on cyclocross bikes is the Avid mechanical disc brake. If adjusted properly it does not drag. The inboard pad is stationary - you adjust it until it is as close as possible to the disc WITHOUT DRAGGING. The outer pad is further away from the disc and moves in as you pull the brake lever. Once it contacts the disc, the disc is warped slightly so that the inboard pad makes contact. I was also skeptical, but now that I have the Avids on my mountain bike, I am sold. They require less lever pressure and don't fade on long downhills.

Maybe there is some super secret adjustment technique, but in my experience the stopping power of V-brakes is superior to cantilevers. If Shimano would just go ahead and make an STI lever that will work with V-brakes, then cantilevers would go away.

My Cross Check runs V-brakes with 287-V levers and bar end shifters. I would rather move my hands to shift than lose the better braking ability of V-brakes. On a cyclocross bike I think disc brakes aren't quite the advantage as they are on mountain bikes, but there are some good reasons to use them (the biggest would be wanting to use STI levers or riding long steep downhills).
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Old 12-08-05, 04:59 PM   #17
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I didnt think you could have to good of brakes.
Yeah, I see what you're saying, but I think that, whilst your brakes can never be too good, there can be major overkill. There would be no point adding weight and ugly looks to my bike to help it stop better in muddy conditions when a) it stops VERY well at the moment, b) it never goes through a puddle, let alone mud, and c) it looks so pretty as it is!
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Old 12-08-05, 07:30 PM   #18
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Well my friend, it appears that you have never owned or ridden a bike with disc brakes.
Because the rim is three times or so the radius of the rim (4" disk, 13" rim) it requires about 27 times the force to give the same stopping power at the tire face. That means that you are losing 27 times the clearance you have with your cantilevers. How do you suppose you're getting that close a clearance without it touching the rim?


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Maybe there is some super secret adjustment technique, but in my experience the stopping power of V-brakes is superior to cantilevers. If Shimano would just go ahead and make an STI lever that will work with V-brakes, then cantilevers would go away.
Properly adjusted short arm cantilevers can lock the front wheel. Explain how a V-brake could offer superior braking.
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Old 12-08-05, 09:24 PM   #19
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One person raved about "modulation". Now I hate to point this out, but the reason that disk brakes were avoided for so long on road racing motorcycles was because they didn't "modulate" well. We had 4-leading shoe drum brakes so huge that the spokes were only a couple of inches long!
so, your argument is that because drum brakes had superior modulation on a motorcycle (which, last time i checked is heavier and faster than a bicycle), rim brakes are better than disc on a bicycle?
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Old 12-09-05, 01:18 AM   #20
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Because the rim is three times or so the radius of the rim (4" disk, 13" rim) it requires about 27 times the force to give the same stopping power at the tire face. That means that you are losing 27 times the clearance you have with your cantilevers. How do you suppose you're getting that close a clearance without it touching the rim?
That is a bizarre statement. It really doesn't matter how much clearance you have, it is what happens when the brake pad contacts the rim or rotor. Like I said, you obviously haven't used disc brakes before. The brakes on my mountain bike don't drag on the rotor and they are much stronger than the V-brakes I used to have on my other mountain bike (and my cyclocross bike).

Your math skills are horrible. Where does that figure of 27 come from? A typical rotor is 6" in diameter while the rim on a 700c wheel is about 25" in diameter at the rim. Since the effective center of the disc brake pads is closer to the hub, lets go ahead and call it 5". That means that the disc brake needs to apply 5 times the amount of force. Which they do quite easily by having more surface area in contact and using higher friction pads.

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Properly adjusted short arm cantilevers can lock the front wheel. Explain how a V-brake could offer superior braking.
My fixed gear friends that ride without brakes can lock the rear wheel, but they can't stop as fast as someone using a brake WITHOUT SKIDDING.

There are some really big hills here in San Francisco. On one of them I found that at a speed of about 35mph I could squeeze until my cables were in danger of breaking and the bike wouldn't slow down quickly enough. I swapped the cantilevers for V-brakes and the braking power was dramatically improved. Now you could say this was due to new brake pads on the V-brakes, bad adjustment on the cantis, etc, but since then I have worked on several touring and cyclocross bikes with new cantilevers and they were not as strong as my V-brakes. That's just my experience, your mileage may differ.
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Old 12-09-05, 06:42 AM   #21
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Originally Posted by Thor29
There are some really big hills here in San Francisco. On one of them I found that at a speed of about 35mph I could squeeze until my cables were in danger of breaking and the bike wouldn't slow down quickly enough. I swapped the cantilevers for V-brakes and the braking power was dramatically improved. Now you could say this was due to new brake pads on the V-brakes, bad adjustment on the cantis, etc, but since then I have worked on several touring and cyclocross bikes with new cantilevers and they were not as strong as my V-brakes. That's just my experience, your mileage may differ.
No way are cantis as powerful as V-brakes. They just aren't! I totally agree with Thor29, there are hills where I live that easily out-do cantis but that the V's work fine on. I use the parallel V-brakes which are pretty good, in my opinion. They do the job in any weather and are light. I have a retro-style Steel MTB as you can see from my sig, and discs would look wrong on it. V's are the perfect solution for me.
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Old 12-09-05, 08:44 AM   #22
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Quote:
Originally Posted by Thor29
There are some really big hills here in San Francisco. On one of them I found that at a speed of about 35mph I could squeeze until my cables were in danger of breaking and the bike wouldn't slow down quickly enough. I swapped the cantilevers for V-brakes and the braking power was dramatically improved. Now you could say this was due to new brake pads on the V-brakes, bad adjustment on the cantis, etc, but since then I have worked on several touring and cyclocross bikes with new cantilevers and they were not as strong as my V-brakes. That's just my experience, your mileage may differ.
Well, Thor, since I was born and raised in Oakland and live in San Leandro and have ridden all over the bay area I do have a little knowledge of "hills" in San Francisco. I've ridden up and down most of them.

Properly adjusted cantilevers will lock the wheels. It takes more lever pressure to do so because the leverage is less than a V-brake.

If you prefer a light lever pressure that's fine but that is a preference and not a technical analysis.
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Old 12-09-05, 10:50 AM   #23
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Best brakes i've used were XTR's.
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Old 12-09-05, 02:14 PM   #24
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Quote:
Originally Posted by Matt Gaunt
No way are cantis as powerful as V-brakes. They just aren't! .
it really depends on how they're set up and what pads you're using. theres more variables in canti set up and more opportunity to screw something up than with linear pull brakes. it's been pulled off the bontrager site now, but there used to be an excellent set up guide written by KB himself detailing how to achieve canti performance equal to or greater than v-brake performance. its still in the google cache if you want to read it. (try keith's rants cantilever bontrager and hit the cached version)
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Old 12-09-05, 03:18 PM   #25
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