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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2Worth every ounce.– MoabCommented Jun 27, 2011 at 1:44
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1Too 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.– zenbikeCommented Jul 2, 2011 at 4:58
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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 HicksCommented Jul 3, 2011 at 3:20
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7 Answers
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.
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.
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.
answered Jun 12, 2011 at 16:56
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1So 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.– ChrisWCommented Jun 12, 2011 at 16:59
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@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. Commented Jun 12, 2011 at 17:13
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1You 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. Commented Jun 15, 2011 at 11:50
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@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. Commented Jun 16, 2011 at 17:49
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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I respectfully disagree with the last two sentences. It’s been a while since I played the weight weenie game, but ti bolts on 6-bolt rotors save what, 20g per wheel? They are also fairly costly. In any case, on the road, the 6-bolt system has been superseded by the center lock system. Commented Apr 2, 2021 at 11:35
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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2Note that rim weight vs weight elsewhere only affects acceleration (not speed) and only very slightly. Commented Mar 14, 2013 at 21:46
Is the extra heaviness in the brakes, or in the stronger rims, tires, and/or forks?
The rims don't need to be stronger on disc brakes. In fact, the rims can be somewhat lighter weight. The reason is that disc brakes don't wear rim sidewalls. With disc brake, you need a rim sidewall only barely strong enough to withstand daily use. With rim brake, you need a rim sidewall that not only withstands daily use when fully worn, but has some amount of wear surface so when you have a new rim brake rim, the rim is significantly heavier due to the extra wear surface.
For tires, there's absolutely no difference. Rim brakes and disc brakes use the same tires.
However, it is important to note that disc brakes use the spokes to transmit braking force. They need either a large flange hub or a large number of spokes. For example, I had a small flange hub and 28 spokes on a disc brake front wheel. Needless to say, the wheel suffered complete and total loss of spoke tension.
Anyway, with rim brakes it is advisable to select 36 spokes per wheel anyway, so disc brakes don't change any of that, they make it just even more advisable.
The weight difference is mainly in two differences:
Firstly, the fork needs to be stronger to withstand the huge bending loads of a disc brake.
Secondly, disc brakes do not reuse the rim as a brake disc. Instead, they use a separate brake disc. It is made from steel so it is relatively heavy.
These more than offset the slightly lighter weight rims on disc brake bicycles, so on the average the total weight of the system is somewhat more on disc brakes.
This article says that small weight difference makes a big difference at the top (competitive) end.
ENTRETIEN. Cyclisme. «Le vélo d’Alaphilippe n’est pas fait pour tout le monde»
Par contre, dans le souci de performance dont je parlais précédemment, certaines équipes roulent encore avec des patins parce que c’est plus léger. 500 grammes, c’est six secondes gagnées en haut de l’Alpe-d’Huez. Ce qui est monumental. C’est 25 mètres d’avance sur le mec derrière toi à iso watts. Les vélos équipés de freins à disque n’ont d’ailleurs pas encore gagné le Tour de France.
My translation:
In contrast, in the question of performance I was talking about earlier, some teams still roll with [the old kind of brake] because it's lighter. 500 grams, that's 6 seconds gained up the Alpe-d’Huez. Which is monumental. It's 25 metres beyond the guy behind at the same Watts. And bikes with disk brakes have never yet won the Tour de France.
It goes on to say that it's hard to reach the 6.8 kg minimum weight -- it's only done with stripped-down bikes, no water, no power meter -- bikes with disks have an average of 7.2 or 7.3 kg.
Is the extra heaviness in the brakes, or in the stronger rims, tires, and/or forks?
From ibid.
Le disque est lourd ?
Oui, presque 300 grammes de plus sur le groupe, 100 à 150 sur le cadre et 150 sur les roues.
I think that's saying nearly 300 grams together, 100 to 150 on the frame and 150 on the wheels.
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Kudos for mentioning the weight that disc brakes add to the frame and fork. I believe the other answers omitted this. Commented Apr 2, 2021 at 11:32
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I think perhaps some of this information is outdated. The recently released Specialized Tarmac and Trek Emonda both reach the 6.8kg limit in off the shelf versions. And in a recent documentary GCN built a Canyon Ultimate (with discs) down to ~5.5kg without any especially exotic parts. And finally, disc brakes did (sort of) win the TDF in 2020 (Pogacar rode discs on Stage 10)– Andy PCommented Apr 2, 2021 at 12:03
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@Andy The article says you see 6.8 kg in shops -- but not after you add pedals, bottle-cages, bike computer (and its support) and power meter.– ChrisWCommented Apr 2, 2021 at 12:07
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On the other hand, if you manage to lower your personal weight by cycling more, because you trust your bike better in poor weather for instance, your overall weight to the ground (bike + rider) will be less. I do not think the grams or even kilograms won are worth it. I have hydralic rim brakes on two bikes, as they are front wheel driven, but I can not rely on them in wet weather. The rear wheel with disk and roller brakes are more reliable, in any weather.– Willeke ♦Commented Apr 3, 2021 at 12:07
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@Willeke Yes I love disk brakes -- especially for commuting where you may be cycling on hills, in the wet (or even snow), in car traffic, and with pedestrians -- problems which the pro racers and their bikes aren't optimized for.– ChrisWCommented Apr 3, 2021 at 12:36