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People say (for example here) that disc brakes are relatively heavy, giving this as a reason for not using them.

How much heavier than rim brakes are disc brakes? Is the extra heaviness in the brakes, or in the stronger rims, tires, and/or forks?

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Worth every ounce. – Moab Jun 27 '11 at 1:44
Too right. The difference in brake modulation and control, is amazing, and I would find it difficult to go back to V-brakes on either my MTB or commuter. – zenbike♦ Jul 2 '11 at 4:58
My thumb suck (never actually worked with disk brakes but have examined a few) is that the additional weight would be on the order of a pound, maybe two on the outside. Rotor, caliper, hydraulic hose & fluid, "master cylinder" add up, although only a few ounces for each. To me (steel touring bike) that's chicken feed, but for someone with a super-light road bike it would at least detract from their bragging rights when they compare bikes with their buddies. (Some of these guys use drilled chains, after all.) – Daniel R Hicks Jul 3 '11 at 3:20

5 Answers

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The difference in weight is there, but hasn't really been significant for the last few years. Scott, for instance, is building a complete, disc brake hardtail with a 4" travel fork. Bike weight: 7.45 Kg, or roughly 16 lbs. That's 2 lbs less than my road bike.

The weight comparison only becomes truly significant when you look at more basic bicycles, i.e. the $600-1500 market, because the cost penalties for premium parts, like truly light weight disc brakes and hubs, don't allow use in that market.

If you are looking at an aftermarket upgrade, expect to spend $1500 on new wheels and brakes, and often more, for quality, lightweight kit. The weight penalty has gotten down to only 50-100 grams in most cases, between a bike built with a high quality disc setup and a high quality V-brake setup.

In my opinion, the advantage in brake modulation and power, not to mention consistency in all weather conditions far outweighs the the addition of a few grams. No pun intended.

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up vote 2 down vote

All of those examples you cite add to the weight.

However, I think the biggest complaint is the brakes themselves. Not only do you need a caliper which needs to be much stronger (and therefore heavier) because it's dealing with huge amounts of compression, you've got to have the extra disk hanging on your wheels, along with the associated mounting hardware for both parts.

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So it's the disk itself, then? The disc has a relatively short radius, though, so I hadn't imagined that its angular momentum was significant. – ChrisW Jun 12 '11 at 16:59
@Chris: The disk itself is relatively lightweight. The mounting hardware is, unfortunately, not. Angular momentum wise I don't think it has too much of an effect -- I'm speaking merely about total weight of the bike. Most of the extra weight is in the center of the wheel, so angular momentum would be small. – Billy ONeal Jun 12 '11 at 17:13
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You also have to take into account the degrees of the word "weight". When some people talk about it it is the difference between the weight of a Hershey's bar of chocolate. Other times it is a significant amount of weight. – Stopher87 Jun 15 '11 at 11:50
@Stopher87: That's true -- but in this case I do think the weight is significant. According to this -> [quote] By the time you add everything in, including front and rear brakes and the added weight of the disc specific hubs, you end up with around 150 to 350 grams additional weight to the whole bike. This weight number greatly depends on the wheels, rims, hubs, and disc brake system you choose. [/quote] For some bikes, that's a significant amount of weight. – Billy ONeal Jun 16 '11 at 17:49
up vote 2 down vote

I did a recent build with a surly cross check but was also checking the soma double cross with discs and the manufacturer specs said Avid Shorty Ulitimate cantis were 260g/pair vs the Avid BB7 mechanical disk rotors & pads/mounts at 1060g/pair. This is just those components and not the frame tabs or disc hubs which might also contribute small amounts to the disc set up. Those are among of the lightest cantis available and mechanical discs are heavier than top of the line hydraulic discs (eg Avid XX at 560g/pair) so the difference is not always that much. I don't know any hydraulics that run on drops so I went with the cantis and never had any no regrets. Even deep mud is not a problem, I just learned how to brake differently.

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up vote 1 down vote

Disc brakes do add weight due to the caliber, pads, steel mounting hardware, and if they are fluid operated, then they are generally even heavier than the cable counterparts. You can reduce significant amounts of weight just by swapping the generic steel hardware for titanium bolts. Dollars per gram saved is quite unreal.

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up vote 1 down vote

Lost in this thread is the weight savings on the circumference of the rim. With no need to have a brake surface, the rotational weight impact may be better with a disk even though the overall weight increases. I'll trade rim weight for hub weight.

Besides, how many gram counters (keep in mind that there are 28 grams in an ounce) can afford to take a dump before the ride and save lbs????

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Note that rim weight vs weight elsewhere only affects acceleration (not speed) and only very slightly. – Daniel R Hicks Mar 14 at 21:46

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