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Not stupid, just redundant. Shimano et al already make dynamo hubs with disc brake mounts.

A few issues with your proposed idea:

With a tire dynamo if the roller slips or (for our purposes) sticks it's not an immediate safety issue in the same way an engaged gear would be due to the interlocking teeth.

As any electronics geek will tell you "Heat is the enemy of electronics" Dynamo hubs work with discs because the disc acts as a heat sink keeping the bulk of the heat in the gripped area as you found out. If I understand your idea you want to drive the generator with this same heated surface -see where I'm going here?

I'm sorry, but you've invented a pushcart for a horse.

Werner Depoorter


In europa a Hub Dynamo is becoming rather popular:

Much less friction an virtually no maintenance needed.

Tony Bullard

Here's another issue. The little wheel on the dynamo would spin many more revolutions all the way out on your tire than it would near the hub, per wheel turn. Does that make sense? It's that crazy physics of turning discs and distances from the center. More distance traveled at the edge than the center.

Mumble mumble something something.


You mentioned the heat that the disc brake collects so that reminded me of how much heat I always notice on the saddle. Don't know anything about thermal energy so I was wondering if there is enough heat from the saddle to be able to collect it to power, for example, a rear light.



Your comment is actually interesting, because I also have stumbled across a few articles that might take your concept and put it to good use, but not for the reason you note.

You note heat as a source of power, however companies are developing sensors that will store the energy created from vibrations into batteries. Thus, you bouncing up and down on your seat might generate enough energy to say charge a light =)

Check out these two articles:




My 2 cents, (simplified for troll baiting):

You are not the first to think of this and not the last, but the implementation would be overly complicated (but no more complicated than "HEY LOOK AT ME" ideas like spokeless wheels or folding wheels) There are many dyno-hubs on the market that produce plenty of power for lights, and they don't cause enough drag to effectively stop you. If they did make a MEGA dyno that could kick in when you hit the brakes, you would need a good deal of fancy electronics to regulate, store, & dump the energy. (we will see more buzz about these systems now that they are legal in F1 cars). I'm not an EE but I understand the price of these systems would be a hella-hack (that's one bike hack X 10^27). Any mechanical system will have drag and noise (probably a gear train also), but again that's not to say impossible. The cost and the ability to brake effectively are probably the killers, at that level of tech I would vouch for frame vibration and saddle/butt chaffing generation.


I've considered the potential of repurposing the disc brake interface for electric generation / motivation too. It's true that a hub dynamo is the simplest most efficient solution, but it's nice to give people options.

Many bikes are disc brake ready, but not using discs. It would be very simple to engineer a kit that mounts a dynamo to the disc tabs and a small composite gear to the disc interface. It wouldn't be much harder to design a custom 160mm rotor and brake adaptor that works with say, and Avid BB7

The ultimate implementation would be one that allowed for capturing the short, high intensity bursts of braking energy and storing it effectively, while reducing the load under normal riding circumstances. Sounds like a tricky bit of engineering but I bet there's an elegant solution waiting to be found.


How about something built onto or attached to the frame (light weight of course) that allows you to carry your bike on any vehicle... like a bike carrier that's already part of the bike. So if you get stranded you can just throw it on your co-worker's car and get a ride home.


dynamo hubs are nice and very common in new city bikes but still heavier and more friction than normal hubs. Use induction instead!
with magnets on your spokes and a spool on the frame. It's already in stores here.
Now there are cheaper ones for about 20 euro. nice and lightweight.

If you want solid indestructible get a dynamo hub and led lights build into the frame. no protruding parts, sleek!


To Matt,
I have actually seen articles about what you mentioned involving piezoelectrics. Its fascinating and I do think it could work well. I am still curious though if capturing thermal energy could work. Maybe I'll do the tests at some point in my life.

On a related note to what you mentioned, some engineers at Georgia Tech designed a system that captures the kinetic energy lost from a bikes front suspension to power lights. Not quite the same as the articles you sent but worth looking at.



At first I thought "Wow, what an idea", but then I thought that if you turned the disk into a cog to drive a dynamo, you'd want it to be lubricated, which would then make it pretty useless for braking.

But IANAE (I Am Not An Engineer), so I'm probably overlooking something.

Daniel D

What you are looking for is called regenerative breaking. It is used in most hybrid or electric cars. The primary breaking system uses magnetic induction to slow the wheel and generate energy at the same time. As with most bike related tech the question is the added weight worth the benefit? The one advantage is no friction/wear on regenerative breaking. Though most have a friction based backup.

Jordan Spizike

I agree. If enough were created to support a large footprint, it would outstrip the natural gas supply and it would create higher gas prices. I would probably put the gas supply at risk, and that would have an impact in home heating. now link my name to know me,and each other we all get the good things.don't think that I cheat you,pls.


A few problems with the idea:
There is far less of a marin for error with disc brakes than with the whole rim as one little slip would pottentially throw you over the bars.
The holes in the disc brake exist for cooling and allow for expansion without warping under heavy braking.

Nice try but I think the brake/bike light companys would have already thought of that and dismissed it fairly quickly.

Belstaff For Sale

thanks for your article,like your blog very much,well done

roberto rey

Hi: why not to insert little (button size) but powerful neodimio magnets in the disc itself, and a coil embracing it, but not touching?. That could be a generator, whitout any mobile parts. Rupert.

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