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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Sign up to join this communityPeople 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?
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.
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.
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????
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.