Disk Brakes on a Bicycle
September 26, 2005 9:18 PM   Subscribe

What benefits and disadvantages does having disk brakes on a bicycle provide?
posted by pheideaux to Sports, Hobbies, & Recreation (17 answers total)
They work better when really muddy, the discs and pads will last a really long time, probably for the life of the bike. And, of course, they look cool.
posted by darkness at 9:33 PM on September 26, 2005

Traditional hand-brakes on bikes would squeeze against the rim of the wheel (the metal hoop between the end of the spokes and the rubber tire).

On off-road bikes, the rim would often get wet or muddy. It's close to the ground. Wet and muddy braking surfaces don't offer as much friction, and therefore don't offer the stopping performance.

Disk brakes are close to the hub (center) of the wheel, and stay cleaner and drier. You can also use non-traditional materials or shapes of your rim if you don't have to count on it as part of your braking system.
posted by Wild_Eep at 9:53 PM on September 26, 2005

Disadvantages: weight (reportedly, and marginal and barely noticeable if at all), but most significantly price.
Word is that you shouldn't bother with really cheap disk brakes though - at those prices you should just go with v-brakes.
Never used them myself however.
posted by edd at 9:56 PM on September 26, 2005

Another disc brake endorsement here. I just recently retrofitted my road bike with a disc brake on the front wheel. It added at least 1.5 lbs of weight when you figure the beefier fork and hub, but it's worth every ounce. I didn't bother with the rear since the braking with the rear wheel is pointless on hard surfaces, whether wet or dry.

I commute on this bike every day of the year, rain or shine, and the difference in braking performance is incredible. I can brake in wet weather just as well as I can in the dry. Pad wear is negligible, rim wear non-existent. I can't describe the peace of mind it provides when riding in traffic.

Moreover, the mechanical advantage is much greater with disc brakes so less hand effort is necessary, reducing hand fatigue (and thus the chance of losing control of your bike) on long, gnarly descents.

Retrofitting an existing bike is expensive, but if you're getting a new bike, you should definitely get disc brakes.
posted by randomstriker at 10:29 PM on September 26, 2005

A friend claims that a fellow he was mountain-biking with had his v-brakes melt onto the rim during a long descent, though it surprises me that that would happen with quality pads. Still, it certainly wouldn't be a problem with discs.

Said friend has disc brakes on his new bike and loves them.
posted by musicinmybrain at 10:49 PM on September 26, 2005

As already mentioned, disks are more reliable, stay clean, need less maintenance, and have great stopping power. It's amazing the amount of energy that the rotor (that's the disk) can absorb. After a sustained braking effort, the rotor can be too hot to touch.

Also, as they are mounted on the hub, that allows you to put reflective tape around the rim of the wheel. That'll increase your visibility.

If you have the choice, get hydraulics rather than mechanicals. The mechanicals are good, but hydraulics tend (in my opinion) to give smoother feedback, allowing better feathering on long downhills.

The major disadvantage is cost. Not just the initial cost, but repairs if they're damaged. I had a crash that broke a brake lever of my Hayes hydraulics, and it cost me £50 to replace. The lever for mechanicals would have been cheaper, and might not have broken so easily.

It's not a disadvantage, as such, but I find that I have to loosen and retighten the brake caliper whenever I refit a wheel. If I don't, the pads tend to rub.
posted by veedubya at 11:00 PM on September 26, 2005

One advantage not mentioned is if you bend your rim from hitting something too hard, you don't lose the ability to brake. (A problem I frequently had as a kid)
posted by knave at 11:13 PM on September 26, 2005

I've never used them, but I've read that disc breaks have a more fine-graned level of breaking, from barley slowing you down, to hard stop.

Whereas V-brakes go from nothing to over the handle bars very quickly.
posted by teece at 11:15 PM on September 26, 2005

Disk brakes can brake so well as to lock your tire up (especially on a step dirt decent). V-brakes can be a little more forgiving in that they tend to slip a little, thus giving you some forward control - much like anti-lock brakes.

I would still go for the disk anyway. As long as you don't over react, you can keep from locking up.
posted by qwip at 11:46 PM on September 26, 2005

Tandem content: Serious descending and braking on a tandem can cause the rims to get too hot to touch. This can lead to tire blow-out, which can be disastrous. Using a disk for braking instead of the rim solves this problem.

Misadjusted cantis or v-brakes can a) rub the sidewall of the tire, causing a blowout or b) dive into the spokes, with equally bad results.

the discs and pads will last a really long time, probably for the life of the bike

I seriously doubt this.
posted by fixedgear at 2:56 AM on September 27, 2005

qwip's right, they can lead to a lockup if you're not careful. I only use my front brake, so lockups can be very nasty. I've learned to be very cautious about braking whilst going from a firm to less firm surface. Braking on sand has to be softly-softly-catchy-monkey, and braking on wet concrete is an absolute no-no.

I was told that it's best to change the pads once a year, probably around spring time, because with city riding they can get contaminated with pollution mixing with the winter rain. Diesel fumes, and the like. Pads are a lot more difficult to contaminate than on rim brakes, but once compromised, they're next to useless. The rotor should probably be replaced every couple of years, because they tend to get grooves worn in them, that can then tend to damage the pads.
posted by veedubya at 3:44 AM on September 27, 2005

teece, I have heard the exact opposite, that disc brakes go from zero to everything very quickly, whereas "standard" brakes give you more modulation.

Havingsaid that, I've never ridden a bike with disc brakes.
posted by GuyZero at 5:34 AM on September 27, 2005

Any bicycle brake, rim or disc, should be able to lockup a tire. The old Campy Deltas couldn't but they weren't sold for more than a couple of years. I don't think anyone died, but it's a good thing they're not on the market any more. Rim heat isn't really an issue (on singles) now that everyone runs on hook-and-rim tires. Note that road descents are far harder on the pads than any off-road descent. Sixty mph descents over many miles are common in the mountains. Think of the Tour de France: they go through a set of pads on every mountain stage.

As noted above, discs have their main use in mud, where rim brakes can get fouled. Otherwise, they're heavier and more expensive. "A pound-and-half" is a huge deal on a 13 pound road bike. I won't argue the expense part---my road bike has Ergo shifters on it, after all.

Properly set-up V-brakes or aero (road bike) brakes are every bit as responsive as discs. "Good Modulation" is all about how much mechanical advantage you have on the brake. It's a bit easier to setup on rim brakes, because they have a higher torque arm, thus the tolerances don't need to be as tight. Disc brakes have a very short brake-arm motion compared rim brakes---this isn't a problem, but can be a bit tricky to setup.

The biggest disadvantage to my mind is that discs won't work with either the Shimano road or the Campy Ergo systems, so that means bar-end or downtube shifters for road bikes (blech). After using Ergos for a few years, I never want to use any other brifter.

So weight and compatibility are two of the major reasons you don't find discs as a common option on road bikes. They solve a problem that doesn't exist unless you ride in mud. So, for most riders, disc brakes are an exotic and expensive solution to a problem they don't have.
posted by bonehead at 6:04 AM on September 27, 2005

They solve a problem that doesn't exist unless you ride in mud.

Agreed, although I think they might be useful as a secondary brake on a road tandem for heat control on long descents (traditionally the role of a heavy rear drum brake).

Also, note that the safety of using a front disc brake with a quick-release hub has been questioned.
posted by normy at 9:24 AM on September 27, 2005

i ride/race on the road and in the dirt, and here are a few absolutes. i wont add to the obvious benefits stated here:

road bike: only on a commuter: no place on a serious road bike.

cyclocross: a must

tandem: recommeded. if you want to save weight, ditch the passenger (one of you are it ;-)

mountain: for everyone but the casual rail trail rider. if you will see dirt, or lack confidence, or are serious, get 'em. someone here stated that all brakes should lock the wheel and that is true, but i can lock up my wheels with less than half the effort over half the lever travel. i ride discs on my 28lb (big heavy) full suspension ride when I am pounding, and stopping my off-season but on that truck is easier with discs, ...BUT... i have shimano XTR V-brakes on my race hardtail - not to save weight, but for ease of maintenance in races. discs are generally reliable, but if you are a hard rider, and one goes, its not a trailside fix. at times, on my shimano hydraulic 545s, i have bent the disc, had a bad rub with a pad squeeling, and had to get the hydraulic lines bled on occassion, and if anything like this happens, you are removing the caliper (on a rotor wrecked anyway) and riding with one brake home. i'd rather have a cable at the ready to fix a (v-brake) under pressure. note, a disc brake repair might be $50 for the rotor, a half hour to bleed the line ($60/hr here at my LBS) and $20 easy for pads.

that being said, i ride my disc bike 90% of the time, and will never buy another bike without them. and that race bike with the v-brakes will soon get avid's cable operated discs as soon as i lose 5 pounds!

PS: never try to save wieght if you can lose some: all the crap about "thats heavy...or this is too heavy...". go ride more and lose 5 pounds and it'll be the cheapest upgrade you can make!
posted by skyguy14 at 9:19 PM on September 27, 2005

PS: tires count too - the best brakes are nothing with out the right tire! get good ones! i think WTB Veleciraptors are the best on the moist packed dirt here in western PA! IMO!
posted by skyguy14 at 9:21 PM on September 27, 2005

The biggest disadvantage to my mind is that discs won't work with either the Shimano road or the Campy Ergo systems, so that means bar-end or downtube shifters for road bikes (blech).

Avid makes disc brakes for short-pull levers -- I use them with Campy Ergo on my aforementioned bike.
posted by randomstriker at 12:45 PM on September 28, 2005

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