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I have two bikes, A and B. A has drum brakes (back and front), while B has rim brakes. Very soon after buying A I noticed that it was more of an effort to get anywhere with this bike as compared to B. Both bikes have broadly the same kind of tire, and are inflated properly.

So I took bike A. I disconnected the rear brake cable, just in case it was partially engaging. I lifted the rear wheel from the ground, made it spin, and let it slow down until it stopped. I did this a few times with both my bikes. Without making any measurements, it was quite obvious that the rear wheel of A slowed down much faster than B. There's obviously some resistance in it.

So I took it to a shop and explained the issue. They put it on a stand, spun the wheels, and then explained to me that this is just normal with drum brakes - they just make the bike harder to ride, and there's nothing I can do about it.

And now here I am trying to learn more about this issue, yet none of my web searches produces anything related to the claim that drum brakes make the bike slower. So, is this true? If it is, can nothing be done about it? And if it isn't, what's the problem with my bike :) ?

Update

I took a closer look at the components of my bike. Should totally have done this before.

On the back wheel: Shimano Nexus SG-8R36 internal gear hub

On the front wheel: Shimano DH-3R35 hub dynamo

On both wheels: Shimano Inter M roller brakes (not sure about the exact model)

So they're specifically roller brakes, not "classical" drum brakes. I found in https://www.sheldonbrown.com/rollerbrakes.html that these brakes do add a bit of drag. They probably add more drag if they haven't been cleaned or re-greased in a long time, which is the case with this bike.

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    What drum brakes does it have? Apr 28, 2022 at 17:50
  • Drums are a rare brake tech on bikes - is your bike particularly old and potentially worn more ?
    – Criggie
    Apr 28, 2022 at 19:27
  • I don't know the exact age of any of the bikes. None of them is anywhere near new, but if anything, I'd say the faster one looks older and more beaten up. I'll try to add some more information on the brakes as soon as I can.
    – abl
    Apr 28, 2022 at 22:59
  • @NathanKnutson I took a look and updated the post. Actually they are roller brakes. The good news is that since these brakes are mounted to the side of the hub, and not an integral part of it, even with my limited skills I should be able to take them off and see if that solves the drag problem. Then either clean and re-lubricate, or install rim brakes instead.
    – abl
    Apr 29, 2022 at 13:06

3 Answers 3

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A drum brake should have no more drag than a rim or disk brake presuming it is properly adjusted.

There is more mass in a drum than a caliper, so the bike is overall-heavier but this isn't going to affect one's flat top speed in any detectable way. On a climb, perhaps.

A more-likely cause is the faster-stopping wheel has dirty bearings and they need a clean and repack. Or the bearing races aren't as smooth, or the bearing balls aren't as uniformly round and need replacing.

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    Yeah, if anything, and all else being equal, while requiring more work to get it to spin, the heavier wheel should spin for longer because it's carrying more angular momentum. Harder to get going, but also harder to stop.
    – J...
    Apr 29, 2022 at 16:02
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I'm not entirely convinced brake drag would massively slow you down. I have dragging disc brakes on my electric road bike, but never have bothered to straighten the disc rotor with the proper tool because although it slowly slows down a spinning wheel, the slow-down effect on a real bike with cyclist on it is so minor it doesn't bother me.

You should really compare the brake drag to a wheel with a dynamo hub. Put a dynamo wheel in front, spin the wheel and see how quickly it stops. Spin a drum brake wheel and see how quickly it stops.

Generally, dynamo drag is considered non-issue when the light is off. You will however see it in the deceleration rate of a wheel. That's because a rotating wheel stores so little energy, that even minimal drag will be visible in the time it takes the wheel to stop.

I would be concerned only if the wheel would stop as fast as (or faster than) a dynamo wheel with light on. If it stops as fast as a dynamo wheel with light off, it's a non-issue.

Generally, the three largest resistances in bicycle riding are:

  • Air resistance
  • Tire rolling resistance (you said the tires are similar -- really? -- but if you want the bikes to be easy to pedal, you already have 32mm front and rear Continental GP5000 on both bikes, don't you?)
  • Uphill resistance

Air resistance is a complex phenomenon but mostly is determined by the riding position, and uphill resistance is determined only by bike weight.

Is there any chance air resistance or uphill resistance would explain the drag? A bike with drum brakes is more likely to have a "relaxed" riding position where the rider is practically upright, whereas a non-drum-brake bike is likely to have a "sportier" riding position.

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  • Thanks for your answer! I forgot to mention that this bike does have a hub dynamo. But the faster bike that I'm comparing it to also has a hub dynamo, with the light always on. The riding position is slightly different but, I think, not enough to make such a difference through air resistance, especially since the bike is harder to ride even at very low speeds. So I guess, either there's something wrong with the brakes, or the bearings, or the tires are not as similar as I think.
    – abl
    Apr 28, 2022 at 22:54
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I have the same experience with drum brakes, there is a fine balance between enough braking power and no-drag coasting.

I did notice a huge difference after cleaning the inside of the brakes

I confused drum brakes and roller takes, the first applies, the following not

(and applying a tiny bit of roller-brake grease, just enough to keep them from screaming.)

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    Do be careful where it goes. Roller brake grease might be the wrong thing for a drum brake. There should be no grease on the braking surfaces of a drum, only on the pivots and actuators. I've had to cook grease/oil out of a brake because someone lubed it wrong.
    – Criggie
    Apr 29, 2022 at 9:23

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