Bicycle Mechanics - Wouldn't it be smart for all bike mfg to go to disc brakes

If bike mfg went to disc brakes it would seem to me to be a huge improvement. Discs work better in the wet, and the biggest thing of all is your rim doesnt get ruined. Add to that the rim could be of any shape the rim mfg thot best.

I have read many cross country ride reports where rims have failed due to wear out. But if these riders had disc brakes, if they had brake trouble just changing either the pads or both disc and pad would fix the problem at a much lower cost.

Rim brakes are cheaper for the bike manufacturers; your cost to replace worn-out rims is of little concern to them. They are also lighter so they can advertise a lighter bike and probably present fewer warranty costs to them.

The corporate bean counters are concerned with the bottom line, not you.

Hi,

I think it depends a lot on what type of riding you are doing. That being said, I do hope to see disc brakes become options on many more bikes.

Cheers,
Charles

I'm thinking about disc brakes myself lately. I've read opinions that they can be finnicky (always seem to be rubbing, etc) but I don't own any. I've kind considered them as "only needed for extreme down hill situations" which is not typical (especially around here). I'd be concerned about simple maintenance on the road. I want to be able to fix anything while on a long trip. I don't think I see disc brakes on randoneuring bikes or long distance touring builds as much as I see canti brakes. I would be interested in other's opinions about maintainability and reliability over long distance rides.

Disc brakes are:
-Heaver
-More expensive.
-Complicate wheel removal/installation particularly if you have to change a road-side flat tire.
-Require a stronger (read heavier) fork and reenforced rear stays.
-Hydraulic versions are prone to fade from excess heat on long downhills. (more of a problem for road bikes than MTB use).
-Require proprietary pads that are more expensive and more difficult to find.
-More sensitive to minor mis-alignment

They do have improved wet braking although good double pivot rim brakes with good pads aren't far behind. Your point about lack of rim damage is valid but only on bikes used routinely in bad weather or in harsh off-road conditions. On road bikes used in mostly fair weather I have rims with well over 25,000 miles still in good condition. The argument that disc-only rims could be significantly lighter isn't valid. Rims are designed for adequate strength and rigidity and the additional material added for brake track wear is minor.

So, for MTB, Cyclocross and all-weather commuter bikes, perhaps disc's advantages do out weight their several disadvantages. But the desirability of their universal application is far from obvious.

Rim brakes are cheaper for the bike manufacturers; your cost to replace worn-out rims is of little concern to them. They are also lighter so they can advertise a lighter bike and probably present fewer warranty costs to them.

The corporate bean counters are concerned with the bottom line, not you.

I agree, up to a point. I think the price could be justified but probably only on those brands that sell to people that value disc brake benefits. That's a tough sell to casual bikers, and the vast majority of buyers.

"Wouldnt it be smart for all bike mfg to go to disc brakes"

In a word....No.

You do realize how few people buying a bike will ever ride it enough to wear out rims right? It is already hard enough to get the casual cyclist to spring for a bike shop quality bike, upping the cost even more would be counter productive. Many people buying bikes only ride in the dry and rarely on hills, v-brakes are more than sufficient.

Also, I dare you to go to the touring section and tell them we should do away with rim brakes entirely. Rim brakes still have some advantages other than cost and weight, mostly for touring cyclist you can find replacement wheels much easier and you can find replacement pads in any country, which may not always be the case for discs.

+1000 on Hillriders comments.

I'm considering discs for my next commuter bike which is ridden on heavy traffic on city streets rain or shine, but there's no way I feel they're needed or better for my road or touring bikes.

Yes I ride in all weather, and rim braking in the rain isn't great, but it's no issue on the open road. Neither is rim wear an issue, I use tubular rims with a total wall thickness of 0.7mm and in 45+ years of riding I've never had any issues of excess rim wear.

Since my total wall thickness is less that the allowable wear of clincher rims, this can't be an issue for most roar riders either.

Disc brakes do offer better rain performance, but they make for a heavier, more expensive to buy and maintain system. They also increase stress on the fork, so unless they're needed, they're more of a disadvantage than benefit.

HillRider is correct in almost everything he says. The only point I would have minor issues with is the complication of wheel removal. I don't find hub mounted discs wheels any more difficult to remove or install than rim brake wheels.

I live where it is dry most of the year so I don't get that much opportunity to test wet weather braking but I have done it, most recently on a 40 mph downhill off New Found Gap in the Great Smoky Mountains. My cantilever brakes performed the task without issue and at no point...even in a driving rain...did I feel like my brakes were inadequate. Equipment is only part of braking. Knowing how to use them is another...more important...part of braking. Knowing how to apply the brakes and how to move your body to get the most out of your brake is far more important than the kind of brakes you have.

Disc brakes are:
-Heaver
-More expensive.
-Complicate wheel removal/installation particularly if you have to change a road-side flat tire.
-Require a stronger (read heavier) fork and reenforced rear stays.
-Hydraulic versions are prone to fade from excess heat on long downhills. (more of a problem for road bikes than MTB use).
-Require proprietary pads that are more expensive and more difficult to find.
-More sensitive to minor mis-alignment

They do have improved wet braking although good double pivot rim brakes with good pads aren't far behind. Your point about lack of rim damage is valid but only on bikes used routinely in bad weather or in harsh off-road conditions. On road bikes used in mostly fair weather I have rims with well over 25,000 miles still in good condition. The argument that disc-only rims could be significantly lighter isn't valid. Rims are designed for adequate strength and rigidity and the additional material added for brake track wear is minor.

So, for MTB, Cyclocross and all-weather commuter bikes, perhaps disc's advantages do out weight their several disadvantages. But the desirability of their universal application is far from obvious.

Heavier - but gram counting is meaningless in the absence of a superior alternative.
More expensive - compared to what? Campy components? I don't agree.
Complicated wheel installation /removal? I haven't found this to be true. No more complicated than remembering to keep the quick release lever on the left. Less complicated the more "out-of-true" the wheel.
Heavier frame construction - Only racers need apply for this argument.
Fade prone - overheated rims are also a problem on long downhills.
Require proprietary pads - Aftermarket pads are sold for the most popular models. For example, at least three disc pad manufacturers sell pads for the popular Avid BB7 model brakes in addition to Avid, the manufacturer.
Misalignment issues - no more so than rim brakes.

Complicate wheel removal and reinstallation? I certainly haven't found that to be true.

Also hydraulic brake fade from heat buildup? This is the first that I've ever heard of that one. I have heard of hydraulic disc brakes locking up from heat expanding the brake fluid in a closed system.

I'm a non-believer in manufacturers' conspiracies. If manufacturers believe a significant body of buyers is demanding disc brakes, they'll offer bikes with disc brakes - and the corporate bean counters will be leading the push.

Interesting discussion, braking power needs versus dynamic mass. I have no experience with disc brakes, although think about on the rare occasion I ride in off weather. I guess it boils down to the needs of your particular ride/style.

Also hydraulic brake fade from heat buildup? This is the first that I've ever heard of that one. I have heard of hydraulic disc brakes locking up from heat expanding the brake fluid in a closed system.
I've read reliable reports of heat buildup "boiling" the brake fluid and causing a loss of brakes on road bike applications.

As to alignment problems, there have been dozens of threads on this forum from posters having difficulty aligning and keeping discs aligned. Misalignment with rim brakes, particularly dual pivot and V-brakes is very easily rectified. It's not nearly as easy with disc brakes for the mechanically inexpert.

As to cale's comments: Dismissing the weight issues is absurd. Not only racers are concerned (maybe overly concerned) with weight but many regular riders obsess over it too. As expensive compaired to what? Campy isn't the benchmark for cost, mid-line Shimano and SRAM are.

I've read reliable reports of heat buildup "boiling" the brake fluid and causing a loss of brakes on road bike applications.

As to alignment problems, there have been dozens of threads on this forum from posters having difficulty aligning and keeping discs aligned. Misalignment with rim brakes, particularly dual pivot and V-brakes is very easily rectified. It's not nearly as easy with disc brakes for the mechanically inexpert.

As to cale's comments: Dismissing the weight issues is absurd. Not only racers are concerned (maybe overly concerned) with weight but many regular riders obsess over it too. As expensive compaired to what? Campy isn't the benchmark for cost, mid-line Shimano and SRAM are.

I love opinions that are stated as though they are facts. You can't prove that you're right and I'm wrong so you attacked the post as absurd, another opinion. My guess, is that the proportion of riders "obsessing" over weight is tiny compared to the proportion that would argue that better braking performance, in all circumstances, is worth a small weight penalty.

you would have to really heat the fluid up to get it to boil though.

i used to race scca solo2 d modified class with a bmw 325i. brake fade is a huge issue with automotive racing so i have experienced it but on a bicycle? i have a hard time believing people riding would have brake fluid overheating problems unless they are out riding mountains and all of it being down hill riding.

brake fade is caused by the pads overheating though, not hte fluid overheating. when your pads heat up, they produce more of a gas then normal. this gas gets trapped between the pad and the disk creating cushion which keeps the pad from clamping hte disk properly. that is why automotive brakes can be bought drilled or slotted, or both. the drilling is not the best way to go but slotted rotor disks allow the grooves to expel the gas from the disk face letting the pads bite again.

you would have to really heat the fluid up to get it to boil though.

i used to race scca solo2 d modified class with a bmw 325i. brake fade is a huge issue with automotive racing so i have experienced it but on a bicycle? i have a hard time believing people riding would have brake fluid overheating problems unless they are out riding mountains and all of it being down hill riding.

brake fade is caused by the pads overheating though, not hte fluid overheating. when your pads heat up, they produce more of a gas then normal. this gas gets trapped between the pad and the disk creating cushion which keeps the pad from clamping hte disk properly. that is why automotive brakes can be bought drilled or slotted, or both. the drilling is not the best way to go but slotted rotor disks allow the grooves to expel the gas from the disk face letting the pads bite again.


and i am not saying brake fade doesn't happen, just i have a hard time thinking that would be a problem on a bike versus heating up your normal brake pads

my guess, is that the proportion of riders "obsessing" over weight is tiny compared to the proportion that would argue that better braking performance center in all circumstances is worth a small weigh penalty.

I'd guess the opposite. I don't think most riders are clamoring for better braking performance. Brakes work well enough as it is and more riders are more concerned with going faster than they are with stopping faster. I can see discs becoming standard on other bikes, but I don't think they'll take over on road bikes until everyone riding in the TdF is using them.

I have bikes with coaster brakes, caliper brakes, cantilever brakes, V-brakes, and disc brakes. My real-world typical rider take:

Coaster brakes are for low speed fun bikes.

The three different types of rim brakes I have don't seem to differ in stopping power or ease of modulation. Any of these can lock the rear tire in a controllable manner. Set up is easiest with V-brakes. Getting my 1982 vintage Dia-Compe cantis set up properly near drove me to tears & drinking. They work great and haven't had to touch them since. Out of true rims are the biggest headache of rim brakes. Rim brakes are the easiest for wheel removal if there is a quick release in the set up.

I have a mountain bike with cheap Nashbar mechanical discs. After set-up and wearing in they work very well. You can twist the front wheel out of the drop outs under hard braking if the QR isn't clamped down hard. Wheel removal & replacement is a pain, but a manageable pain. Discs look cool. Putting a rear rack on the bike is now a tricky proposition.

Brake fade isn't an issue for me. Wish I was that badass of a rider that could fade the brakes. With alloy rims, wet weather braking is good with rim brakes. I clench my teeth when I hear that grinding sound of grit between pad & rim. Sorry if I'm repeating the obvious, but rarefied discussions of theoretical differences is a useless exercise.

Disc brakes are:
-Heaver
-More expensive.
-Complicate wheel removal/installation particularly if you have to change a road-side flat tire.
-Require a stronger (read heavier) fork and reenforced rear stays.
-Hydraulic versions are prone to fade from excess heat on long downhills. (more of a problem for road bikes than MTB use).
-Require proprietary pads that are more expensive and more difficult to find.
-More sensitive to minor mis-alignment

They do have improved wet braking although good double pivot rim brakes with good pads aren't far behind. Your point about lack of rim damage is valid but only on bikes used routinely in bad weather or in harsh off-road conditions. On road bikes used in mostly fair weather I have rims with well over 25,000 miles still in good condition. The argument that disc-only rims could be significantly lighter isn't valid. Rims are designed for adequate strength and rigidity and the additional material added for brake track wear is minor.

So, for MTB, Cyclocross and all-weather commuter bikes, perhaps disc's advantages do out weight their several disadvantages. But the desirability of their universal application is far from obvious.

I don't know much as I am fairly new to disc brakes on bicycles, but unless you are physically carrying the bike or racing .. I seriously doubt 2 pounds will make much of a difference and as far as brake fade... brake fade ( as it pertains to automobiles) is where a gas builds up (due to heat) between the brake pad and the rotor causing the brake pads to lose physical contact with the rotor.. as far as I know, brake fade has absolutely nothing to do with brake fluid.

your points are all valid except for the brake fade only on hydraulic systems and the complexity of tire removal, however most of your points are rather minuscule and appears to just be argumentative against disc brakes

...you can find replacement pads in any country, which may not always be the case for discs.

OTOH, a matchbox worth of volume will hold something like 4 pairs, which ought to see you across a continent or two before wearing out. Not much of a problem bringing that along.

Also.. (a +1) disc Brakes don't lend them selves to the Fast wheel changes
that are a part of replacing punctured sew up tires in the big road races ..

but as a consumer, without that criteria, you may be happy with disc brakes..

They are making inroads into Cyclocross racing , but at the top levels
the rider just grabs another whole new clean and ready to go bike
when they pass their pits on the next lap.


yea think ahead, bring spare pads... you can find aluminum backed ones ,
to weigh less than the ones on steel backing.

There is a lot more to the bicycle market what works over a larger spectrum. First, bicycle R&D starts with race bikes. You may say that is stupid or non-racers don't need ultra light bikes, but the market says otherwise. Selling a race bike with caliper brakes with a lighter frame while lower level bikes are heavier with discs brakes simply will not sell. There is a article in the recent Bicycling mag on the Colnago race bike, the first with disc brakes. First you have to remember that caliper brakes work as well a disc in most conditions on aluminum rims, even in the rain with the proper pads. Further it is more common for road bikes to have long sustained down hills that mtb with discs and the hydraulic oil does not need to boil; the hoter it gets the more power in braking is lost. Once hydraulic oil gets hot it does not cool very fast. This is opposed to aluminum rims that have much more surface area that discs and cool very quickly. The primary purpose for disc brakes is the use of carbon wheels. Carbon wheels have been around for about 10 years (or more) and most the accidents you see in recent crashes are the result; carbon wheels just don't stop well and in rain they don't stop at all! Disc brakes will solve this problem. But the reality of why you won't see disc brakes on most road bikes is simply there is no market for them.

Also.. (a +1) disc Brakes don't lend them selves to the Fast wheel changes
that are a part of replacing punctured sew up tires in the big road races ..

but as a consumer, without that criteria, you may be happy with disc brakes..


Undo QR, drop wheel, slot in new wheel, go? no brake to unhook/loosen via lever. I fail to see how people have an issue replacing disc wheels, maybe you all run your wheels crooked?

Boiling brake fluid can be a problem. It's simply heat transfer from the pads to the fluid, closest to the pad.

http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid

Well watch the Pro races, .. see If Mavic neutral support
is carrying any disc wheels on top of their yellow Cars..

lots of brands of various manufacturers already have disc brake models,
as well as the rim brake road racing bike models,
at the top of their range.

is the OP wanting a planned economy where only one bike is made?

Like gas pipe Flying Pigeon brand from Chairman Mao's grandson ?

The primary purpose for disc brakes is the use of carbon wheels. Carbon wheels have been around for about 10 years (or more) and most the accidents you see in recent crashes are the result; carbon wheels just don't stop well and in rain they don't stop at all! Disc brakes will solve this problem. But the reality of why you won't see disc brakes on most road bikes is simply there is no market for them.

This is the honest to god truth. Disc brakes are going to be the future on high-end road bikes. Why? Because those top of the line road bikes are going to be equipped with carbon wheelsets, and if not, the people who buy those bikes are going to eventually splurge on carbon wheels, and full carbon wheels are what is gonna necessitate disc brakes. And despite all the disadvantages listed by Hillrider above, the fact that disc brakes won't ruin carbon clinchers due to overheating, and also the superior capability in stopping during wet rides are gonna carry the day.

I say in seven years or less, disc brakes are gonna be as common as can be. At least on mid to high level road and cyclocross bikes.

Undo QR, drop wheel, slot in new wheel, go? no brake to unhook/loosen via lever. I fail to see how people have an issue replacing disc wheels ..


ChefIsaac, you read that ? [He apparently has troubles doing just that]

They are already available for cross and road bikes. They come standard on most mt bikes above, say $500.00. They work great in bad weather, but for your basic, cruiser or hybrid, not needed.

Disc brakes....Complicate wheel removal/installation....

Huh?

Getting the wheel past the pickup for the cyclocomputer is a bigger roadside pain than the disc brake.

Only issue I see with roadside fixes is if I, or some misguided assistant, would squeeze the brake lever while the rotor is out of the caliper.

....As to alignment problems, there have been dozens of threads on this forum from posters having difficulty aligning and keeping discs aligned...

And how many posts has there been on various types of rim brakes not centering?

....I don't think most riders are clamoring for better braking performance....
You know, there's more than one flavor of "better".
In terms of sheer braking power, pretty much everything that's come after the spoon brake has been capable of causing wheel lock, but there's more to it than that.
There's no way I'll ever take a canti-equipped bike touring in the Alps again for instance.
Brakes that were just fine at home simply became fatiguing to use when dropping one mile in altitude in one go.
And I'm going the same route on my commuter.
Sure, the rim brakes and the drum brakes have done OK, but what's the point of continuing to squeeze the levers that hard, when a switch of brake technology will give you the same deceleration at much less of an effort? Plenty of hand clenching is not a major contributor to ride enjoyment.

Got em on truck, got em on my car, got on my motorcycles, even got em on my mountainbikes, and it's all good. Do not want or need them on my road bike, thank you.

I also read that Colnago has a bike fitted with disc brakes, and that he is trying to convince everyone to change to them. He reckons a couple of years. I think we're all missing a point here - manufacturers aren't really interested in the pro's and cons, only profit. Just think, if the pros were told to use discs then they would. And all the world will follow.... in a couple of years this forum will be discussing whether you can fit Campy, Shimano, Sram discs to some stalwarts 1945 Schwinn, or whatever. I hope not, I still regret the slow demise of the ultimate, elegant, steel racing bikes of the 80's. I have one which I love, but also a modern alu/carbon which is a joy to ride. Remember ! you read it here first.... just a thought

Lower quality disk brakes are often noisy and hard to adjust. Try explaining to someone that their inexpensive new bike's brakes are going to shreik no matter what.

I don't know if it's been mentioned yet, but there's a couple of reasons why I'm holding off on disc brakes and I'd be unhappy if that's all there was available. They're a bigger pain to maintain, heavier, and there are some failure scenarios related to overheating. Especially on the more inexpensive variety. So, reluctantly, I'm sticking to rim brakes as the better option.

Undo QR, drop wheel, slot in new wheel, go? no brake to unhook/loosen via lever. I fail to see how people have an issue replacing disc wheels, maybe you all run your wheels crooked?

You forgot one step. Get disc lined up with caliper & pads. I have actually used both disc & caliper. Disc is harder to re-install the wheel. Flicking open a caliper style brake release is effortless.

Disc brakes have reached Road Bikes...

http://volagi.com/bikes

....as far as I know, brake fade has absolutely nothing to do with brake fluid.
That's not correct. See DaveSSS's posting above. Why do you think automotive brake manufacturers have been developing higher and higher boiling point brake fluids over the years. It's not because the brakes run so cool and the thermal demands are so low. Bike brake demands seem trivial compaired to cars but they are not. Bike discs are extremely thin and low mass compared to car discs and can get extremely hot in a short time. Sure, it's possible to over heat rims with caliper brakes on a long Alpine-type decent but discs certainly don't end that problem and may make it worse.

Also my "opinion stated as fact" about the heat of braking causing the brakes to fade due to overheating the brake fluid was not an opinion. It was based on a direct report by the editor of what i believe was the slowtwitch.com web site of what happened to him during a long mountain decent on a new disc equipped road bike. I couldn't find the original article but I didn't make the incident up.


your points are all valid except for the brake fade only on hydraulic systems and the complexity of tire removal, however most of your points are rather minuscule and appears to just be argumentative against disc brakes
Please don't think I'm against disc brakes as a concept. There are certainly bike applications where they make sense and have advanatages. The MTB community has widely embraced them for good reason and cyclocross riders are still deciding but seem to be accepting them. My point was that universal application and across-the-board use of disc brakes by all types of bikes, as the OP suggested, was not a good idea and there were useful reasons not to do it. Maybe at some time in the future they will be as universal as rim brakes are now but that time hasn't come yet.

The defense rests, your Honor. ;)

...but there's a couple of reasons why I'm holding off on disc brakes..

Holding off as in never tried?


... They're a bigger pain to maintain, heavier, and there are some failure scenarios related to overheating. Especially on the more inexpensive variety. So, reluctantly, I'm sticking to rim brakes as the better option.

Which would explain the above opinions nicely.

Heavier, sure.
Overheating? I dunno. Any scenario where a disc brake may overheat I'm confident would stress a rim brake quite severely too. Pick your poison basically.

Likewise with the maintenance issue. I'd say it's a balance between frequency, complexity and experience working with hydraulic systems.
When a hydro disc goes bad, fixing it does take a bit more(and above all a completely different skillset) than working with a rim brake. But odds are that before that happens, it'll have given more trouble free service than your average rim brake.

And how many posts has there been on various types of rim brakes not centering?

or their indexed shifting out of whack?

In a word....No.

Yes.
Disk brakes are an inelegant solution to stopping, compared to rim brakes. We're already using a terrific braking surface that has more leverage, and therefore more control than making heavier hubs with mounting interfaces, needing more fasteners, and more metal, and more stuff to go wrong.
I've got a mountain bike & commuter with disk brakes, and IMO rim brakes with dual-pivot calipers are superior in every situation except wet.
Plus bleeding & adjusting hydraulic lines is a messy PITA compared to working on simple, effective brake cables.

Although contrary to Hillriders point about brake fade, I've never been able to effect that, even on lonnng sustained downhills. I've experienced brake fade on my motorcycle while squidding on the track, but that was pretty extreme. Never had it happen while riding on roads, or when bicycling.

I have a question on this topic. Rather than either/or, wouldn't a mixed solution, with disc on front and rims on rear, be a less complicated solution to implement for those long downhill riders? After all, since the front is the wheel that does all the work, and you use the rear brake far less heavily, you only need heavy braking power on the front, which is easier to deal with in bike design than the rear wheel, which is already crowded and busy doing other stuff...

*puts bucket over head, in anticipation of having one's idiocy being pointed out in detail*

Holding off as in never tried?



Which would explain the above opinions nicely.

Heavier, sure.
Overheating? I dunno. Any scenario where a disc brake may overheat I'm confident would stress a rim brake quite severely too. Pick your poison basically.

Likewise with the maintenance issue. I'd say it's a balance between frequency, complexity and experience working with hydraulic systems.
When a hydro disc goes bad, fixing it does take a bit more(and above all a completely different skillset) than working with a rim brake. But odds are that before that happens, it'll have given more trouble free service than your average rim brake.

Never tried it. Holding off == having researched and rejected, including some discussions with mechanics who have them. I don't make these decisions lightly :)

I don't know if it's been mentioned yet, but there's a couple of reasons why I'm holding off on disc brakes and I'd be unhappy if that's all there was available. They're a bigger pain to maintain, heavier, and there are some failure scenarios related to overheating. Especially on the more inexpensive variety. So, reluctantly, I'm sticking to rim brakes as the better option.

I don't understand why you think disc brakes are harder to maintain. Hydraulic disc brakes are self adjusting and mechanical disc brakes take just a turn of a knob (similar to the adjustment required for rim brakes) and that adjustment infrequently. Heavier, possibly, but rim manufacturers aren't constrained by the same criteria required of rims with machined surfaces which can lead to lighter wheels. Failure scenarios are far more prevalent for rim brakes. Overheated rims are the leading cause of tire blow offs (along with improperly seated tubes).

I've got rim brakes on two bikes and disc brakes on one. I am more confident of the performance of from the disc brakes though I admit my Sram Force calipers are pretty sexy on my Kuota.

I have a question on this topic. Rather than either/or, wouldn't a mixed solution, with disc on front and rims on rear, be a less complicated solution to implement for those long downhill riders? After all, since the front is the wheel that does all the work, and you use the rear brake far less heavily, you only need heavy braking power on the front, which is easier to deal with in bike design than the rear wheel, which is already crowded and busy doing other stuff...

*puts bucket over head, in anticipation of having one's idiocy being pointed out in detail*

In MTB, one of the big advantages is how little power that needs to be applied at the lever. Two fingers on the lever is pretty much the norm, with some getting by with one. Allows for a safer, yet more relaxed grip on the bar. Again, overall stopping power isn't tha main goal or gain.
Half-and-half setups were commong in the early days of disc brakes. Riders could always find a reason to go for a new fork, but if you've just shelled out for a nice frame(w/o disc brake tabs) many would like to get some use out of that first, before swapping to a full disc setup.

And then there's the abrasive power and slippery characteristics of mud.
If you're an all-weather, "technical" rider, you may find yourself working the rear brake every bit as hard (if not harder) than the front, just b/c a lockup at the rear is a much more controllable incident than a front wheel lockup.

And the rear isn't particularly crowded. Due to the assymetric nature enforced by the cassette, there's plenty of place at the hub for the rotor mount.

True, with seatstay mounted calipers, there's often fender/rack conflict. But a modest redesign allows for chainstay mounted brakes, which leaves the field wide open for racks and fender mounts.

I don't know why I'm feeding the fires of this argument, but I just feel like pointing out that the reinforced nature of a disc brake frame doesn't only add weight (which is more of an issue for some people than for others) but it also changes the way the frame rides, making it more rigid and (ostensibly) harsher.

I don't know why I'm feeding the fires of this argument, but I just feel like pointing out that the reinforced nature of a disc brake frame doesn't only add weight (which is more of an issue for some people than for others) but it also changes the way the frame rides, making it more rigid and (ostensibly) harsher.

The harsher ride is interesting. I hadn't considered that. I wonder how much of an effect that is (and in which cases).

Cheers,
Charles

Disc brakes have reached Road Bikes...

http://volagi.com/bikes

Almost all bicycles already came with disc brakes. All hub mounted disc brakes do is move to a smaller rotor.

In MTB, one of the big advantages is how little power that needs to be applied at the lever. Two fingers on the lever is pretty much the norm, with some getting by with one. Allows for a safer, yet more relaxed grip on the bar.

Two fingers on the lever is the norm for most properly adjusted brakes. Proper adjustment is the rub. I've seen suggestions that levers be for cantilever and v-brake be adjusted so that the brakes don't actuate until the lever has reached half way to the lever. That's about half way too far. If your levers hit the halfway point before actuating, you are going to bottom out the brakes before the brakes are fully actuated.

I have dual pivot side pulls, cantilevers (both flat bar and drop), linear brakes, mechanical disc and hydraulic discs. All of them are set so that actuation occurs with little lever movement. I can stop my road bikes (dual pivot and cantilever) from the hoods with the middle, ring and pinky finger. I can stop all of my mountain bikes (cantilever, linear, mechanical and hydraulic disc) with only 2 fingers on the levers. The cantilever, linear and mechanical disc all have nearly the same lever feel and require about the same hand pressure to stop. Not one of them stops better or easier than the others. The hydraulic brakes, on the other hand, are touchy at best. Very little movement of the lever is needed to go from off to locked which makes for interesting off-road riding. If anything, it makes riding that bike much more difficult to ride off-road.

And anyone who rides for even a little while on a mountain bike quickly learns to have a relaxed grip on the bar. The type of brake you have shouldn't influence grip at all. If it does, you are doing something very wrong.


And then there's the abrasive power and slippery characteristics of mud.
If you're an all-weather, "technical" rider, you may find yourself working the rear brake every bit as hard (if not harder) than the front, just b/c a lockup at the rear is a much more controllable incident than a front wheel lockup.

The brakes aren't the limiting factor in wet and muddy conditions. The adhesion of the tires is far more important. That's one of the main problems with the touchy hydraulic brakes that I have. They transition from off to full on so quickly that the front tire can skid out in wet conditions which isn't a good thing. Front wheel slide is almost a guarantee for getting to first base with the ground.


And the rear isn't particularly crowded. Due to the assymetric nature enforced by the cassette, there's plenty of place at the hub for the rotor mount.

The hub isn't the problem. The caliper mounting point is. If you want to mount racks on the bike for utility, mounting them around the caliper can make life difficult. I have front and rear disc tabs on my commuter bike. From the pictures below, you can see that if a caliper were mounted on the front, mounting fenders would be very difficult...it's not easy to mount them without the caliper in place. On the rear, I couldn't mount the rack I have mounted if the caliper were in place as can be seen in the second picture.

http://i144.photobucket.com/albums/r181/cyccommute/LC-right-fork.jpg
http://i144.photobucket.com/albums/r181/cyccommute/IMG_0270.jpg

Mounting the disc tabs inside the seatstay/chainstay junction would be better but many companies haven't made the change, frankly, because they don't think about things like mounting racks on bikes.