View Full Version : Disc brakes - benefits / detriments?
SpongeDad
12-06-05, 04:22 PM
Aside from being further from the mud, are disc brakes really that useful? On most bikes, I can lock the brakes anyway.
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."
ccharles
12-06-05, 05:40 PM
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.
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.
cyclintom
12-07-05, 07:31 AM
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.
cyclintom
12-07-05, 07:39 AM
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.
shokhead
12-07-05, 07:52 AM
Whats the reason we havent seen Disc on roadbikes? Weight? Cost?
Matt Gaunt
12-07-05, 07:59 AM
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.
SpongeDad
12-07-05, 09:22 AM
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.
<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.
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.
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 :D. 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.
ccharles
12-07-05, 11:35 PM
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.
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/articles/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.
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).
Read this: http://www.velonews.com/tech/report/articles/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.
cyclintom
12-08-05, 07:29 AM
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.
shokhead
12-08-05, 08:14 AM
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.
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).
Matt Gaunt
12-08-05, 03:59 PM
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!
cyclintom
12-08-05, 06:30 PM
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?
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.
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?
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.
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.
Matt Gaunt
12-09-05, 05:42 AM
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.
cyclintom
12-09-05, 07:44 AM
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.
shokhead
12-09-05, 09:50 AM
Best brakes i've used were XTR's.
jittery
12-09-05, 01:14 PM
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)
Romoni_63
12-09-05, 02:18 PM
You guys remember the Magura hydrolic rim breaks?
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.
I don't know where you get your information on disc brakes but reading some of this is almost comical. Indirect loading? Direct loading? the caliper has to rattle? fancy mounting hardware?
I had to check the dates on this thread too make sure that it wasn't from the year 2000 or something.
the advantage to disc brakes are
Superior Modulation. If you haven't tried properly set up hydros you should. The modulation will blow you away.
Predictable power in all conditions. I agree that Canti's and V brakes have plenty of power. But not in the rain and muck. Disc brakes perform well in all conditions. All. You don't have to wait for the wheel to rotate to clean the braking surfaces. They just work. All the time. The main reason to switch to disc brake is smooth predictable braking in the mud, rain, snow or whatever. I could eat up one whole set of pads going on a long MTB ride in the rain. With discs it is no problem. no rim brake gunk, just nice clean rotors.
If your pads are rubbing, your brakes are not set up right. period. Go to your LBS and have them set you up right.
The Avid BB7 mechanical Disc brake is probably the most simple, dependable, easily adjustable brake I have ever used. Canti, Linear pull or otherwise. It is widely considered one of the best bicycle parts ever made.
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.
1) which would be.......?
2) Magura Marta SL's weigh 324 for the entire brake (lever, caliper and rotor). If they were not light, XC racers would not use them.
3) again , where do you get this from?
4) You can get a great mechanical disc brake for $75.
5) You do need a disc fork, you got me there.
6) wrong.
7) disc brakes are so common now that finding parts should be cake.
But you can't use them on your cross bike anyway right?
trigeak13
12-09-05, 04:43 PM
they are too legal
You guys remember the Magura hydrolic rim breaks?
rim-crushers. a lot of trials riders still use them.
shokhead
12-09-05, 07:17 PM
You guys remember the Magura hydrolic rim breaks?
I have some somewhere,came on a CD hybrid. Hard as hell to get them adjusted. Took them off for some XTR's, what a difference.
cyclintom
12-09-05, 08:51 PM
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)
Of course its been pulled. Do you suppose Trek and company want people to understand that newer ain't necessarily better?
Keith is pretty savy. But remember that now he makes his living pushing parts. And if you have something NEW to sell, EVERYONE has to buy it and not just new bicyclists.
winston
12-10-05, 02:45 AM
People sometimes use "being able to lock the brakes" as a measure of brake strength, but what it means depends on a lot of things.
- What kind of surface are you riding on?
- How much contact do your tires have with the surface?
For example, locking a 20mm wide tire on wet pavement requires a lot less force than locking a 35mm tire on hot sticky asphalt.
- How fast are you going?
- How much do you and the bike weigh?
- What is the slope of the ground you're riding on?
- How is your weight distributed on the bike?
It's usually a lot easier to lock up the rear wheel than the front, since your weight shifts to the front during braking. I don't think I can lock the front wheel on any of my bikes when I'm going a decent speed on pavement -- not that I've tried to. I do know that braking as hard as I can hasn't slowed me down as quickly as I would have liked in some cases. Sure, I can do an endo when I'm going 5mph, hit the front brake, and shift my weight over the front, but that doesn't mean much.
Strong brakes are especially helpful when you're going fast downhill and want to slow down quickly. In these cases I've squeezed the hell out of my cantis and still not slowed down quickly enough. In my experience, when set up right, cantis are about as strong as calipers but not as strong as V-brakes and discs. YMMV.
In my experience, V-brakes are stronger but have touchier modulation. Discs are stronger and have better modulation, but it's easy to grab the front brake lever too hard, lock up the front wheel, and crash, if you're not concentrating on what's going on. It's happened to me before and others that I know.
I'd say that for cyclocross racing, discs aren't that useful, since they do add weight and you don't really need the extra stopping power. But for general off-roading and bad-weather riding, they're nice. Rim brakes are bad in freezing/wet/snowy conditions (you often need a revolution to clear off the rim), but discs are almost entirely unaffected. Another poster implied that the opposite was true, but that's just wrong. As an added bonus, you don't get any black rim gunk from the brakes.
Disadvantages to rim brakes:
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.Such as......
2) They have a lot of really good weight.Sorry wrong again. They may not be weight weenie light, but they're not heavy
3) They always drag on the disk and add some additional drag so that you can build your leg muscles faster.Sorry wrong. If your's are dragging you didn't folow the instructions. I could train the Prez to install them correctly
4) They are expensive.
Sorry that's incorrect as well Avid BB7's (the best mechanical set on the market) can be had for $160 a pair
5) You need special forks and frame to mount them or add some nice heavy brackets.I'll give you the mounts, but many new 'cross bikes have the needed mounts to begin with
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.Wrong again. Of course you said the exact same thing earlier
Disadvantages to rim brakes:
4) They might take one revolution to wipe the rims clean before they start working. That's almost a second at slow speed.
7) They are all non-standard so finding parts is always a fun adventure.Perhaps on your planet. Anyone on Earth with an internet hookup can find dozens of disc brake parts
Seems to me that disk brakes pass all of the OCP requirements with flying colors.Sounds to me that you haven't got a damn clue what you're talking about.
The following has been reposted by me more times than I care to admit
Why are discs better than rim brakes?
The difference is friction. Friction is of course the force acting against the momentum. Friction under all circumstances will be greater in a disc system than a rim system. Not even ceramic rims and their pads can compare to the sustainable friction of a disc system. Not to mention the effects of inclement conditions on rim brakes.
Let's start by taking a look at the physics involved. There's a law of physics that states how an object in motion has a certain amount of energy due to its momentum. This energy is called kinetic energy. In order for this object in motion to stop or slow down, it must lose some or all of its kinetic energy. It does this by converting the kinetic energy to heat.
It's pretty simple. At your wheel you have a metal disc and a set of friction pads. The pads squeeze or push onto the metal. When this happens, you create friction. Friction generates heat, of course. Since the wheel is turning, then the kinetic energy of your momentum is converted to heat at this point and discharged harmlessly into the atmosphere (with a slight loss of pad material), and your bike slows down. The faster it is going, the more heat is needed to stop it. The more pressure you apply to the pads, the faster it can discharge the kinetic energy. The disc aids in the discharge of the heat generated. The surface area of the rotor allows heat to dissipate more quickly.
Rim brakes work well, but they have a hard time shedding heat well enough to prevent fade when used really hard. Brake fade occurs when the brake overheats dramatically; braking power is vastly reduced. The fact that rubber compound rim brake pads can only sustain so much heat and pressure before they break loose is another key point as is the fact that disc pads, being made of a more durable substance, are not prone to the same failures.
Facts
Disc brakes handle heat load and dissipation better than calipers.
They don't transfer the heat generated directly to the rim, like calipers.
Disc rotors are MUCH cheaper to replace than an entire rim (as low as $17). As far as being able to lock a wheel: yes you can lock a wheel much easier with a disc than you can a caliper of any type, however if your brakes are PROPERLY setup, you also have greater modulation with less effort than any caliper system ever invented.
cyclintom
12-11-05, 10:39 PM
Hey, you're perfectly free to pay $350 and put about 2 lbs onto your bike in order to replace $60 worth of Avid cantilevers that weigh a couple of ounces.
And I'm free to think of you as a whack job.
graff71884
12-12-05, 10:51 AM
I don't run discs, but $350 is almost double what you would have to pay to put a decent set of Avid's on your bike from the prices I have seen.
cyclintom
12-12-05, 11:52 AM
http://www.nashbar.com/profile.cfm?category=69&subcategory=1013&brand=&sku=15122&storetype=&estoreid=&pagename=
XT Level Disk brake setup - ON SALE $340 normally $530.
http://www.nashbar.com/profile.cfm?category=69&subcategory=1013&brand=&sku=14122&storetype=&estoreid=&pagename=
Avid Setup front and rear $280 normally $360.
Anyone notice that they don't publish the weight of this stuff?
graff71884
12-12-05, 02:01 PM
So you found prices from one place, that doesn't mean you can't get them cheaper other places. I can find front and rear mechanical Avid's for around $200 shipped.
cyclintom
12-12-05, 07:47 PM
So what if you want to have Shimano brakes?
Look, why are you avoiding the point that disk brakes are a great deal heavier than cantilevers, cost a whole lot more and add no significant advantage?
graff71884
12-12-05, 08:07 PM
To tell you the truth, I was never arguing with you that disc's were better because I personally don't see that much need for them. All I was saying is that you could get them cheaper than what you had posted. I have a Trek XO1 and think the Avid's canits stop with plenty of power for my needs.
So what if you want to have Shimano brakes?
Look, why are you avoiding the point that disk brakes are a great deal heavier than cantilevers, cost a whole lot more and add no significant advantage?
Shimano, ick. plus, there's a big difference in price and weight between Shimano hydros and the cable-actuated brakes you'd find on a 'cross bike. now, if anybody's making hydro brifters or aero levers, i wish somebody would let me know.
sure, they're heavier than cantis. but not by some obscene amount - at most 1 lb. and that's with really light "boutique" cantis. what's a pound in the non-race real world most of us live in?
and as for whether they have a "significant" advantage, that's a matter of opinion. but as for me, i'm not going back to rim brakes on my mtb. there's a f'n huge difference in control with disc over my old rim brakes (old-school Dia-Compe cantis). if you haven't rode disc and don't want to, that's fine. not everyone needs them - and racers can't use them. but if they really were worthless, folks wouldn't buy or spec them. especially if your assumptions on price and weight disadvantage were true.
radical_edward
12-12-05, 10:07 PM
There are two reasons that are keeping discs off drop bar bikes:
- Safety. Mountain Bike/Fork manufacturers have recently been through a period of sleepless nights due to stronger disks overcoming the quick release or just plain tearing the dropouts/disk mounts off the fork. Most now have strict limits on disc sizes. Marzocchi have gone to post mount on their big forks to try and solve issues due to the additional braking (breaking!) power of 8" rotors. Disc mounts on carbon forks are not ready for prime time.
- Traction. I run Shimano Deore M535 Hydros with 185mm avid rotors on my MTB and can lock up a 2.5" tyre with one finger. If I run 2" tyres I have to be very careful as it becomes considerably easier to lock things up and I have washed out the front on many occasions. There is no point in running discs with 37mm or god forbid 23mm tyres as you do not have the traction to make use of the braking power that discs afford. Two wheel drifts on drop bars are not fun.
cyclintom
12-13-05, 08:11 AM
Please try to understand this - putting a disk on a spoked wheel is a precarious business at best from an engineering point of view. ALL of the braking power which used to go from the frame to the traction surface must now go from the frame to the hub through the spokes to the traction surface.
Has anyone else noticed that spokes break rather regularly on wheels stressed only by the weight of the riders and the riding surface? Do you really believe that braking forces are inconsequential?
Normal bicycle brakes are perhaps the most elegant solution to minimum weight vs stopping power ever devised on any vehicle and are possible only because of the precise physical characteristics of the bicycle.
Trying to improve on this by using a more indirect means causes exactly what I've been describing: Additional weight, additional cost and additional unnecessary complexity.
Here's a perfect example from your posting:
"I run Shimano Deore M535 Hydros with 185mm avid rotors on my MTB and can lock up a 2.5" tyre with one finger."
You actually believe that this is somehow an improvement? That you need only one finger instead of using your whole hand on the lever? Perhaps you are skilled enough to never be taken by surprise and grab a whole handful suddenly but the fact is that very few riders are. It is an advantage to have to conciously apply enough power to stop the bike in an emergency.
I wonder how many people know that only 10% of all bicycle fatalities do not involve motor vehicles but the majority of those deaths without such involvement have the rider going over the bars and landing on his head?
You actually believe that this is somehow an improvement? That you need only one finger instead of using your whole hand on the lever?
I do. Certainly the reduced fatigue from only having to apply light pressure over the course of a race, or simply a hard day in the saddle is of huge benefit @ the end of the day.
Excluding cost, the only detriment to running discs is the extra weight. If you don’t race, that detriment is nullified. Yes, disc brake systems are more complex, but IMHO, they are actually more reliable for a few reasons. First, the pads last WAY longer, so you may only have to change a set once/year. Secondly, if you bend a rim, you can still go (and stop!) on a disc-equipped machine. Lastly, you won’t risk heating up your rim, and blowing a tire @ speed with a disc set-up.
However, I wouldn’t run discs for those reasons alone. I would run discs for their superior braking power, and modulation – especially in the wet/mud. The point is that a good disc braking system is superior to any form of rim caliper braking system in terms of performance. If you’re worried about the extra grams, go with a rim-caliper solution, but just don’t expect the same level of performance.
shokhead
12-13-05, 09:25 AM
All carbon Disc?
Aus Rotten
12-13-05, 01:25 PM
WOW! Those are some real technical replys! They are not worth the weight! If you race then its just dead weight to lift.
darkmother
12-13-05, 01:49 PM
Well guys, here's my $0.02. I've got rim brakes on all my bikes, and they work just fine for me. However, I have used high end hydraulic discs on various MTB's and the best of them are an improvement over rim brakes. Why? *MODULATION*. The best discs are just way more linear and controlable than any rim brake I have used. That is a good thing in a traction limited environment, whatever bike you happen to be riding at the time. With discs, the brake response is relatively unaffected by mud or water-also a big plus.
That said, I don't think most people are getting the most out of their rim brakes. The cantis on my cross bike are actually better, IMO than my the XTR v brakes on my MTB-and those are damned good. Cantilevers offer a lot of adjustablility, b/c you can change the mechanical advantage of the system by playing with the stradle cable length, hanger position etc. There are also many more ways to get it wrong-which is one reason why most people like V brakes better. With V's, you just slap them on and go.
radical_edward
12-13-05, 04:16 PM
You actually believe that this is somehow an improvement? That you need only one finger instead of using your whole hand on the lever? Perhaps you are skilled enough to never be taken by surprise and grab a whole handful suddenly but the fact is that very few riders are. It is an advantage to have to conciously apply enough power to stop the bike in an emergency.
Yet I can feather those same brakes well enough to nose wheelie down a slope and come to a halt while still balanced on the front wheel.
Try that on your Cantis :D
And yes, it is an advantage to keep three fingers and my thumbs around the grips whilst braking.
And disc brakes are so complicated that I have run a set for 3 years without doing anything other than taking old pads out, pushing the pistons back with a tyre lever and popping new pads in. Oh yeah, I had to do that once about a week ago.
And get a new wheel builder if your spokes are breaking while you are 'just riding along'.
But I am happy with the cantis on my jake. Having to toe in the Avid shortys every 50km or so, going through a set of pads in 4 days, and 3 sets in as many months, chucking the whole lot for the new Shimanos, swapping the pads immediately for Kool Stops. I had forgotten how much fun it is to wrench a bike!
They have an elegance about them that is lost on modern bicycles. Having to carefully pick my line whether on the road or the forest as I know that I will be unable to stop in time has done wonders for my mountain biking. I feel a part of the machine on my cross bike whereas my mountain bike is an insulator between myself and hostile terrain that would be difficult to even walk across.
Horses for courses.
The only reason to outright dismiss disc brakes on bikes is that you are a grouch. Which is fine. Really.
Fly your freak flag high.
winston
12-13-05, 06:04 PM
Please try to understand this - putting a disk on a spoked wheel is a precarious business at best from an engineering point of view. ALL of the braking power which used to go from the frame to the traction surface must now go from the frame to the hub through the spokes to the traction surface.
It's true that the power transfer is less direct, but that doesn't make it precarious. Most cars and motorcycles have disc brakes that transfer power through the hub, but no one accuses them of being fragile. The system must be designed properly to handle the forces, of course -- putting a bicycle disc brake on a motorcycle would be precarious; putting it on a bicycle would not be.
Has anyone else noticed that spokes break rather regularly on wheels stressed only by the weight of the riders and the riding surface? Do you really believe that braking forces are inconsequential?
Sure, poorly built wheels suffer broken spokes. Well-built wheels don't. For example, the wheel engineering master, Jobst Brandt, has over 200,000 miles on a set of spokes. They've outlasted his rims many times over.
Normal bicycle brakes are perhaps the most elegant solution to minimum weight vs stopping power ever devised on any vehicle and are possible only because of the precise physical characteristics of the bicycle.
Trying to improve on this by using a more indirect means causes exactly what I've been describing: Additional weight, additional cost and additional unnecessary complexity.
I agree that normal brakes are elegant (well, not so much for cantis, but I use them anyway). But discs are stronger, have better performance in bad conditions, and have better modulation. There is additional weight, cost, and complexity, but whether or not it's a valuable trade-off depends on the rider. There are times where I've gone down steep hills and wished for more braking power; even when I squeeze almost as hard as I can and tire my hand out, it's sometimes not enough. Also, knowing that I could stop quickly if, say, a car pulls out, lets me ride down these hills faster. Many times, I've ridden my brakes down descents because I knew my brakes could not handle events like this.
I wonder how many people know that only 10% of all bicycle fatalities do not involve motor vehicles but the majority of those deaths without such involvement have the rider going over the bars and landing on his head?
Where did you get these statistics? How many of these "landing on head" incidents were caused by too much braking power, as opposed to just hitting something and going over?
Your earlier comments reveal your lack of knowledge about how well disc brakes actually perform. I don't mean this in a harsh way, but please, before going on a new tangent and attacking a new straw man, you have to somehow convince us, despite our experiences, that discs have no performance advantage. We all recognize that there are trade-offs, such as weight, but just because you don't like the trade-off doesn't mean that no one can gain anything from using them.
cyclintom
12-13-05, 07:16 PM
I do. Certainly the reduced fatigue from only having to apply light pressure over the course of a race, or simply a hard day in the saddle is of huge benefit @ the end of the day..
Now here is a point that I'll agree with wholeheartedly. But let's remember that V-brakes add the same stopping power at a fraction of the weight and cost as well.
And when you're racing you have a closed circiut upon which you've familiarized yourself so that you're unlikely to have any violent surprises that might lead you to jam the brakes on in a panic.
I still don't see the point in disk brakes.
Excluding cost, the only detriment to running discs is the extra weight. If you don’t race, that detriment is nullified. Yes, disc brake systems are more complex, but IMHO, they are actually more reliable for a few reasons. First, the pads last WAY longer, so you may only have to change a set once/year. Secondly, if you bend a rim, you can still go (and stop!) on a disc-equipped machine. Lastly, you won’t risk heating up your rim, and blowing a tire @ speed with a disc set-up.
However, I wouldn’t run discs for those reasons alone. I would run discs for their superior braking power, and modulation – especially in the wet/mud. The point is that a good disc braking system is superior to any form of rim caliper braking system in terms of performance. If you’re worried about the extra grams, go with a rim-caliper solution, but just don’t expect the same level of performance.
I keep hearing "modulation" from people who say they race and yet when I was racing I very seldom used my brakes and modulation certainly wasn't required. They were either on all the way or off all the way.
chipcom
12-13-05, 07:33 PM
This is a great thread! To me the choice is pretty simple though - on my regular ride I have cantis, while the all-season, bad-weather commuter I am building will have disks. The right tool for the right job IMO.
The right tool for the right job IMO.
You summed it up for me in one sentence. On a road-racer, all-rounder (like a cyclocross or touring bike), three-season or all-season bicycle, rim brakes are all you need (although discs are a good idea on the all-season bike) . Lots of big downhills, off-road or on-road? A nasty weather commuter bike? Discs sound like a good idea in these conditions.
My only beef with disc fanatics is the idea that somehow discs are inherently superior to rim brakes under all or even most riding conditions. They're not. It's all about using the right equipment for the conditions.
I am concerned about safety - front wheel ejection is a real problem, and one that I would love to see dealt with. It wouldn't stop me from putting discs on a bike, but it would probably stop me from putting 8" rotors on a bike.
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