Rim brake overheating

In my other life I ride a road tandem, and one of the things to watch for with tandems is overheating rim brakes on long descents. The rims have been known to heat up so much that the tyres blow off. Not something you want happening to your front wheel on a heavily loaded bike during a long mountain descent! To combat this a lot of touring tandems have a low-tech rear drum brake operated by a friction shifter and used as a drag brake in such situations. This is in addition to the rim brakes, which are used for cornering, stopping etc.

The reason I bring this up is that I’m contemplating a 36er, which will eventually have a brake. I’m undecided between rim and disc brakes at this point, but rim brakes are pretty tempting since with a bit of finangling I can fit a pair of cheap V brakes to the Magura mounts and be in business.

It occurred to me, though, that unicycles and tandems have a similar load:wheel ratio (one human per wheel) and brake usage (at least on the road where there is a constant steady pressure during long descents). Has anybody experienced unicycle rim brakes overheating after extended use? I suppose disc brakes have the potential to overheat too, but hopefully without any dramatic result.

Maybe I’m overthinking things… :roll_eyes:

Over-thinking. We unicyclists do that a lot around here. :slight_smile:

Rim brakes are cheaper and much simpler to set up. Downside is that your wheel has to stay true to get smooth braking. And non-smooth braking, especially if you go fast, is dangerous.

Disc brakes look cool, have more stopping power, and are less likely to have problems related to trueness. Only if you bend your rotor is this a problem. Depending on the unicycle, a disk can be very complicated to set up and adjust properly. Not recommended for a Schlumpf hub on a non-late-model KH frame! After tons of filing I’m still having trouble getting it to work smoothly. I think I need a new rotor…

Why doesn’t a 36" uni have the same brake problem as a tandem? Mostly because you aren’t going as fast. If you can ride really fast downhill while riding the brake, you might get into heat problems but that’s a pretty advanced skill.

I WISH I had a drag brake that I could set at a specific level of drag for riding long hills, but there doesn’t seem to be an easy way to do this with a hydraulic disc brake. And I don’t want to carry around a second brake just for that purpose.

What John said.

I don’t think overheating should be much of an issue on rim brakes b/c the speeds just aren’t so high (I personally have only ridden long descents with disc brakes though).

The main advantages to the discs:

  1. far fewer problems with trueness, which with a 36 happens way too easily/frequently. Because of the large diameter, only a slight deviation in the rim makes the brakes really irregular and hard to use.
  2. way more power and dosage

And if you are still worried about fading then the disc is way better: just increase the disc size to get more power, less heatup and more heat dissipation.

Unless your setup doesn’t allow for a disc (e.g. no way to add a D’Brake), then I’d go for a disc over a rim brake on a 36. It’s worth it. I run a disc with the KH Spirit and D’Brake on my older 24 using the “washer” method (search the forum, Hugo has a detailed description) (my Oracle 36 came with the D’Brake).

Useful info, thanks. To John’s point about speed, a lot of heat problems on tandems happen when descending very slowly (with constant brake friction). At higher speeds the airflow helps cool the rims somewhat.

Now that I think about it, I think I am going to start with a V brake because of the minimum outlay required, and then possibly upgrade to an external disc later on if I feel the need.

The other difference is, as the unicycle is fixed gear, you have to pedal all the time even while braking, but especially for control, so the pedal backforce also produces a good portion of the braking, and the brake is only for extra braking, whereas on a freewheel the brake does all the braking.

The rim brake should work fine. As stated, you just need to make sure to keep the rim very true.

One more thing to consider is that the rim brake may have the disadvantage that you leg armor gets hung up on it. This happened to me a few times during steep ascents or in sandy terrain. This is at least partly the reason i am now switching to a disc brake.

Ah, I’d always imagined that on downhills I’d be braking hard enough that I’d be pedalling forward against the brake. As you can probably tell I’ve never ridden a unicycle with a brake. I probably need to just try it and all will become clear.

Keeping the rim tensioned and true is no problem. I plan to do that regardless.

Not something I’d thought of but I can see how it could happen.

Well, that is doable to, and something I sometimes use. I guess the perfect brake force to apply would maintain your speed downhill, so you only need to use your legs for balance adjustments.

Sort of on that topic: maguras are great on unicycles because they tend to be easier to dosate than v brakes, which on a uni is quite important, since more/less brakeforce than expected often ends with unplanned dismounts.

BTW Your thread made me think about using this on a uni. :smiley:

Interesting idea! An alloy rim is already a conductive body in motion. I wonder what strength magnet would be required and if it would be practical to use a pair of permanent magnets on movable arms?

Back to reality… While I understand the advantages of Maguras, I think if I end up desiring more control I’ll probably just spring for a cheap crank mounted disc.

Not strength, weight. And there goes the practicality. That’s probably why they work well on trains; weight isn’t much of an issue.

There was a guy at NAUCC 2003(?) who had an electromagnetic drag brake. His magnets weren’t very heavy, which meant the braking power was not very noticeable. The advantage of that system is you get a steady level of drag with zero friction, which means zero problems associated with unsteady application, trueness, etc.

And keeping a 36" wheel true takes more effort than a smaller wheel. Generally, as the wheel gets bigger, its tendency to come out of true gets higher.