fallsjohn

I know absolutely nothing about disc brakes (except the ones on my Civic), but the concept seems to make sense. Are they better? Will all bikes have disc brakes someday? Can I assume a bike with regular brakes but with disc brake mounts would allow for the installation of disc brakes somewhere down the road? If so, is it a tough job, expensive, neither? Thanks in advance for putting up with this myriad of questions.

Nermal

Not all bikes are going to have disc brakes in the forseeable future. They do have a weight penalty. Good disc brakes cost more than good rim brakes. Also, they don't wear on the rims, which can be expensive. I'm told they do perform better when wet, muddy, or icy.

wahoonc

Disc brakes have their place. Wave of the future? Dunno depends on production costs versus a lot of things. If the bike has disc brake mounts, yes you could convert in the future but I am sure it won't be cheap, quick check on prices you would spend a minimum of ~$180 to get the components not including proper hubs.

I currently run rim brakes and roller (drum) brakes. They do fine for my current riding. Rim brakes are prone to issues with weather and will eventually wear out a rim requiring that it be replaced. Roller brakes don't have that problem. They do require specific hubs, but typically don't have issues with weather, and as far as I can tell don't wear out particularly fast.

Aaron

Retro Grouch 

I wouldn't make that assumption. In addition to the caliper mounting points you also need to have disc compatable hubs. Of course, you could always buy a disc wheelset but that would take the adding disc brake package to another price level.

bluefoxicy

All bikes will eventually have disc brakes as the manufacturing companies making the brakes become more marginalized. Disc brakes are relatively easy to make; less expensive bikes are getting them in the $400-$600 range. Mountain bikes occasionally in the $200-$300 range show up with disc brakes and full suspension by some magic.

Some road bikes are getting disc brakes. Disc rotors are near the center of rotational mass and thus do not impose as much of a moment penalty as a heavy rim; cantilever brakes such as the now-popular linear pull cantilever brake ("V-Brake") impose none. Disc brakes have much better stopping force under all conditions. Disc brakes do not wear rims.

As time progresses, simpler cable-driven disc systems will replace cantilever rim brake systems. As the production equipment starts to run down and the manufacture of disc brakes becomes cheaper, companies will start retooling to make more disc brakes, rather than maintaining or replacing old rim brake equipment. This critical point may come decades into the future, but likely within 15 years from what I can tell about market pressure (somebody is milking a patent on linear pull brakes).

Jimi77

I don't see much of reason for disc brakes myself. When I used to mountain bike I rode some steep hairy stuff and managed to get by with old school cantilevers. I know bike trailers (usually?) aren't compatible with disc brakes.

StephenH

My Raleigh Sojourn came with disc brakes, and after using them, I honestly don't see a lot of reason to use them or to avoid them.

Reasons to use them: A while back, I did a 1200k ride, we were riding through a pouring rain on hills at night, and one friend goes whizzing past down a hill calling out "I don't have any brakesssss". At the Texas Time Trials last year, it rained on me for about 75 miles of my 12-hour ride, and I heard one other rider saying he didn't like going down hills at 30 mph without any brakes. On our brevet yesterday, at a SAG stop, the SAG driver was cleaning a rim for one of the drivers. I inquired, and turned out, he was cleaning melted brake pad off of that rim- that was a climb with long steep hills (and descents).

Problems: I can go for a month or two with no issues, then start having problems getting the things adjusted right (Avid BB5 Road, by the way.) And periodically, you do have to adjust mine. The main issue there is I normally brake using both front and rear wheels, and if one or the other isn't doing much, I may not notice for a while. So you can be riding around thinking you have "better" brakes, start down that mountain, and then discover that actually, your rear brake isn't doing much braking at the moment. You can also get different quality levels and different size rotors, so not all disk brakes are created equal. When you do start working on disc brakes, they're small and crammed down there close to the wheel where it's hard to see what you're doing or how they're aligned, etc.

I think in summary, you can look at what most experienced cyclists use, and not too many use disc brakes on a road bike, so for most riding, either will work okay, and people go with the lightest/easiest option, which is rim brakes.

coldfeet

No, it will never happen that that all bikes will have discs. Yes, there will be more of them with disc, but cost and weight, and just fashion will keep them off some bikes. The advantages are better function in crap conditions ( I use them because around here the Winter roads have the most disgusting mess on them from salt, grit and snow melt ) No rim wear, no rim heating on long descents, no brake problems with the rim being a little out of true.

jsdavis

Disc brakes do have their share of problems. The rotors can warp, just like cars, and cause scrubbing as it rotates. Alignment of friction material can also cause rubbing. The brake system can also heat up to where the brakes fade just like rim brakes, but I don't know whether or not the heat capacity of 160mm rotor is greater or by how much. At least I think 160mm is the most common.

The only reason I have disc brakes is because the bike came with them; and I did not buy the bike for disc brakes. One thing I'm not enthused about is that the rear caliper is often mounted outside the rear triangle and gets in the way of racks and fenders.

Ediblestarfish

Discs have a pretty good weight penalty, and they still can't stop faster than the tire can grip, so it's not the end-all be all.

Discs attach to the weaker areas of a frame, near the hubs, and must have reinforcement to work. Also instead of gripping the rim, which has a minor leverage penalty for rim brakes, it reroutes the stopping torque down through the spokes, though the hub, and then finally into the disc brake, which has a major leverage penalty. That means a disc brake equipped bike should also have reinforced wheels, spokes, and hub, which adds further weight, in addition to the frame's reinforcements.

Since they are near the hubs, they require extra clearance and can cause fitting issues with accessories like racks and IGHs, and need specially designated equipment for them.

It's all more complex, heavier, bulkier, and usually more expensive. That said, they certainly brake harder, better, under wet conditions. Great when weight on a bike is not an issue.

Digital_Cowboy

I ride a Specialized Hardrock MTB with disc brakes. I also tow a Yakima Big Tow trailer and it is fully compatible with my Hardrock as well as it's disc brakes.

MichaelW

Disc brakes need stiffer forks which give a harsher ride. Not a problem with suspension forks but non-sus ones have to be quite substantial.
The braking forces act to force the front axle out of the dropouts. High-end MTBs use thru-axles which eliminate this problem. Lightweight quick-release skewers cant cope with the braking forces. The solution is a slotted front "dropout" angled forward OR to reverse the wheel and put the disc on the driveside. Driveside disk cannot be used with dynamo hubs.
The problem of mixing a rear disc brake with rack and fenders are real. "Disc-compatible" racks have 1" spacers to clear the brake caliper but this weakens the rack and adds air resistance and reduces the ability to "go for the gap". Much better is to position the brake on the chainstay BUT current cable-routing into the caliper is at the wrong angle for this position.

I like my discs for all-weather commuting.

Burton

Most of these posts make it sound like all disk brakes are created equal - they aren`t. Although they all carry a weight penalty, cost and performance vary tremendously. Working in a variety of shops I can tell you that even the simplist disk brake is more complicated to inspect, set upand adjust than any rim brake. And the wet weather performance of cheap mechanical brakes with resen pads is no better than the average rim brake - in fact cantis with KoolStop pads will outperform them.

A decent set of hydraulic brakes will cost almost as much as a good hybrid bicycle equipped with rim brakes. So if you expect disk brakes to appear on all bikes in the future - better be prepared to pay a hefty premium to get anything worth driving.

Brifters are pretty much the same thing in that their popularity has largely added hundreds of dollars to even the cheapest road bike - and most tourers opt for barend shifters anyway for greater reliability. Sometimes more is less.

Bob Nichols

I thought all bikes had disc brakes, except the coaster brake. Isn't the wheel a disc?

Seriously, I thought about getting the disc brakes on my Trek 7.5FX, but didn't think is was worth the extra $180. I try to use my brakes as little as possible - loose's too much energy. Ha!

bradtx

fallsjohn, Disk brakes are pretty common already and I expect moreso in the future because if nothing else the brake system is perhaps percieved as better than rim brakes by many, mostly newer to the sport consumers. No doubt disk brakes can be superior in certain situations such as offroad racing, downhill racing and as a drag brake on a tandem and can be advantageous when riding in the wet. I don't think they'll make rim brakes obsolete in the same manner of the threadless headset's dominance on manufacturing frames.

Brad

Looigi

Discs have a much more linear and reproducible feel, no grabbing or locking up, same performance wet dry or dusty, won't overheat on the most epic descents (I've gotten my mtb discs glowing red hot) ... Basically the same reasons they use them in motor vehicles, aircraft, etc.. Are these benefits enough to justify their cost and weight? For me, yes on mtbs but not on road bikes...though if I had a tandem I'd want discs on it.

Retro Grouch 

Time to muddy the waters. It might not be a simple either-or option.

I can envision dynamo hubs to recharge a battery on brakeing and double as a booster motor. In my future world a hybrid bicycle might have a whole new meaning.

bluefoxicy

It's only a problem when the front brake is fubar. Rear brake adds nothing to braking force when maxing out. There may be an exception on high traction extremely steep grades, but I've honestly yet to flip a bike forward that way; I've nearly done an endo with just my back brake, though....

Waiting for high-performance street-style ceramic-copper pads. I put Friction Master Ceramic pads on my car. These are NOT racing pads, do NOT use them in your race car; racing pads will provide NO braking force on the street (I bought a car that the last idiot had 'em in, swapped 'em out), while street performance pads will provide NO braking force in race conditions where the pads get EXTREMELY HOT.

The Friction Master pads I use are a street-performance copper-impregnated-ceramic pad. They are made by Morse Brakes and rebranded by Friction Master. They provide little braking force at race temperatures; but at street temperatures (cold, or warmed up from every day driving) they provide EXTREME braking performance. Just like normal composite brakes (such as the OEM brakes on your car), you want to downshift on long, steep mountain descents; riding your brakes will cause them to fade, losing friction as the temperature raises too high, and then you have no brakes.

Disc brakes on bicycles and motorcycles function the same way. The rotor is a metal substrate intended to accept friction material. The pad is a friction material source. Braking deposits friction material on the metallic substrate; further braking creates friction between this layer of friction material (on the disc) and the friction pad (the brake pad).

As such, replacing the friction material with superior friction material for the purpose will greatly improve braking performance.

Mountain bikes and tandems will want something with decent cold performance, but extended performance up into higher temperatures. They'll also want bigger rotors and larger pads to provide more braking force, as well as better leverage (hydraulic systems).

Single road bikes for commuting will want better cold performance, decent hot performance, but not quite up to the temperatures mountain bikes and tandems may reach. They can use smaller rotors and pads. Most city descents shouldn't stress the brakes enough to make them glow.

A hybrid system is also feasible. The front can use larger rotors with better low-to-mid performance, with a smooth fade in the upper range. The rear, which is turned from the center and thus more sensitive to weight and moment (i.e. weight further from the center), can use smaller rotors with pads that function somewhat in the low range but give decent mid-to-high performance. While strong stops will favor the front wheel still, long mountain descents will favor riding the back brake mostly--which functions under much greater heat stress.

Hybrid systems like this make sense, of course, because the front brake provides much more stopping power anyway, and the rear can skid easily. Even with a low-cold-performance brake, you can probably skid the back wheel cold; but once the rear brake heats up, it's your controlled descent. Up front, you can brake fast whenever; but if you're riding long down a mountain and want to ride your brakes, ride the back brake more and save the front for when you need to actually stop (or can't modulate speed enough without skidding the rear tire).

QED.

Doable, but they'd have to be electrically linked and self-contain the battery. Front would be a dyno-motor; rear would be a dyno-battery with less braking force, since the rear wheel skids. Now, how do you make the wheel actually lock under sufficient braking force so the brakes still full function?

cyccommute 

Try a set of Avid Juicys some time. Grabbiest damned brakes ever made with a complete digital feel - choose either 1 or 0.

Discs aren't any more linear of reproducible than a properly adjusted rim brake because a rim brake is a disc brake. Same principle and nearly the same mechanism. The problem is that most people have had to endure rim brakes that are improperly adjusted. My favorite bit of stupid advice on rim brakes is to 'adjust them so that the pads don't engage until half travel on the levers'.

I'm not sure what you mean by discs not locking up. All of the discs I've ever used were rear wheel locking machines. And I've not run across many brakes that could lock the front wheel...nor would I want to If your rear wheel is locking up, you haven't figured out how to brake properly yet - as evidenced by the 'mtb discs glowing red hot' on descents. I've ridden epic descents for miles and miles and never had a problem with braking nor with rims overheating. But, then, I don't ride my brakes all the way down the hill.

The problem with your statement is that brakes are rarely used at maximum deceleration. The other problem is that maximum deceleration is a theoretical limit and should be defined as maximum deceleration before pitchover. Maximum deceleration is also highly influenced by rider position or, more correctly, by the position of the center of gravity. Moving the center of gravity forward and up will decrease the maximum deceleration substantially. Move the center of gravity back and down will increase the maximum substantially.

Up until downward force on the rear wheel goes to zero, the rear wheel's contribution to overall deceleration can be a relatively large percentage of the overall braking power of the bicycle and is tied to the center of gravity. For example, a rider seated on the saddle braking hard can develop about 0.5g of deceleration. 0.1g of that deceleration, or 20%, comes from the rear wheel...as long as the rear wheel is in contact with the ground and the center of gravity stays stationary.

Finally, you statement that you've "nearly done an endo with just my back brake", is silly. There is no driving force to rotate the rider around the front axle if the front wheel with only rear braking. If the front wheel is stopped by something, you could endo but that's not due to using the rear brake.

Looigi

Holy cow. I don't know where to begin, so I won't bother. Let's just agree to disagree.

cyccommute 

So you think that it's possible to endo when using only the rear brake?

And I'm not alone in feeling that the Avid Juicys are grabby.

StephenH

You hear the statement a lot of times about 70% or 90% of the braking capacity being in the front. This is based on skidding a wheel, and as long as nothing is skidding, you have equal braking front and rear, provided you use them equally front and rear. My point about starting down the mountain and not having much rear brake means you only have one brake, not that there's a significant difference as to which brake it is that isn't doing much. Either way, you've got half the brakes you thought you had when it comes to heat buildup and that sort of thing.

Burton

OK So lets have some fun with pros and cons.
One argument for disk brakes is that bending a rim in mtb biking can make your brakes ineffective.
Quite true - so can bending a rotor - which apparently is much more common.
Of course theres the arguement that rim brakes eventually wear out rims which is perfectly correct. But then disk brakes eventually wear out rotors too and the rotors on a bike are usually more expensive than the rims on any OEM set-up I`ve seen.
And of course it is possible to upgrade to metallic pads (and compatible rotors) and oversize rotors and get some excellent braking with excellent modulation with hydraulic systems. But comparing the $500 worth of disk brakes I`m driving on one machine to the performance of a set of KoolStop pads on $25 rims with $35 canti - I`m honestly not seeing much of a difference wet or dry. On either machine its possible to brake hard enough with the front brake to lift the rear wheel off the ground.
Of course changing out broken spokes is a nuisence anyway but with disk brakes you now have to remove both the rotor and the cassette in the rear - and then reinstall both to the proper torque specs.

Maybe coaster brakes weren`t so bad after all.

coldfeet

Eh, there's a lot of *interesting* comments on here that I'm just gonna leave alone.

Yes Discs have drawbacks, but if you ride here in the Winter, you will be either using discs, or stripping and rebuilding your V-brakes every 2 weeks. That's why i use them.

fietsbob

go test ride some mountain bikes, at LBS, now, they're already here,
on $400 Mtb's, and somewhat pricier commuter bikes..

Best when frame design is anticipating the force involved,
and reinforcing where needed.

Example :German Tout Terrain , makes a rigid fork, and oversizes left blade, tube, a bit.. .