I suspect that they had a spray system that directed a mist onto the discs. Years ago a company in the USA developed a a disc that was filled with sodium, which melts at 208°. When the disc heated to that temp, the melting sodium would absorb tremendous amounts of heat in the process keeping the disc from heating any more until/unless all the sodium melted.

I don't know if anything ever came of this, but brake heat dissipation remains a major consideration in braking. Folks who live in mountainous areas, especially truckers, know the importance of downshifting to let engine drag slow descents, and in many areas there are runaway truck lanes, and turnouts where trucks can pull over and let their brakes cool for a while.

Cyclists have freewheels, so we can't get engine braking, which is why cyclists have to learn how to use air drag, or manage terminal velocity to avoid overheating their rims, which is a common problem on long fast descents.

Yes that's it.

Here you can see the water system:http://m.youtube.com/watch?v=4gwEbsqNgdk

And in action at Brands Hatch, UK
http://m.youtube.com/watch?v=Go3dDrPdiQk

Cheers

As a tourer, I am familiar with dealing with mountainous descents, and am in the habit of letting a bike run until a single hard application of braking is required, and if being spirited in switchback type descents, recognising when judicious stops to let things cool down are a good idea.

Cool (no pun).

I'm amazed that they can get any kind or rear axle traction with that weight distribution.

I know I know, as a longtime f1 and other Motorsport follower for about 35 years, including some motorcycle racing myself, I often have thought the same thing. Pretty goofy looking.

While the aluminum rims on bikes do dissipate the heat fast, carbon fiber rims do not.

i imagine the spoon brake left the party when the pneumatic tire showed up.

Yes, except not alone, it ran away with the dish brake.

I'd like to purge this thread of the spoon brake comparison, which is a red herring. The spoon brake was designed to work on the road-contacting surface of a solid, slick tyre. Because the tyre picked up grit, and the spoon was made of ordinary metal, it heated up too much, wore out quickly.

I am suggesting a brake pad made of a more more suitable metal (or other substance), designed to work on the sidewall of a pneumatic tyre made with e.g. extra thickness, a different compound. If the sidewall is designed to wear at a slower rate than the tread, they will both be replaced at the same time.

The advantage is the same as with a disc brake (not compromising the rim) plus the lack of the disc mechanism with all the extra weight and adjustment/maintenance issues.

As for stopping with a flat, the pads would still exert enough pressure to slow the bike, and you have another brake on the other wheel as well.

Build and market it and see how it fares, a significantly better system will sell.

The spoon brake comparison isn't a red herring at all. While there's a difference between the tread and side of a tire as regards road grit, the issue of heat is the same.

Mechanical braking is about converting kinetic energy to heat through friction. The amount of heat generated is very significant, and must be dissipated or absorbed by a "heat sink" otherwise the surface temperature will rapidly rise to well beyond the melting point or rubber.

Since rubber is an insulator, the heat will flow into the metal part which if it isn't large enough or cooled somehow will heat up quickly leading to failure. It's not an accident that all brakes use small pads of friction generating material against larger moving heat conducting rotors.

Feel free to experiment, but you might save some time by doing some research into the physics of mechanical braking.

Additionally, as the tyre heats, the air inside of the tube will expand.

M.

This is much less of a problem than one may imagine.

First of all the relationship of pressure to temperature is based on absolute zero, (-460F) so going from 75f to 125 F would mean less than a 10% rise in pressure.

Also consider that rubber is a lousy heat conductor, so the temp on the inside surface of the tire will be slow to climb. Then consider that air is also a lousy conductor, so there'll be a long delay before the air inside matches the temp of the tire's inside wall.

Over all, by the time the air starts to warm in any meaningful way the braking cycle will be over and everything will be cooling off already.

Oh, well, then. Learn something better every day.

M.

As FB points out this idea is inherently flawed, but it got me thinking...

So here's a neat idea for a commuter bike: instead of a traditional rear brake (which most competent riders can go without pretty happily), you could have the rear brake lever actuate an old-school dynamo and use it to charge one of those nifty USB backup batteries used to charge phones and whatnot (some electrickery would likely be required to get the voltage right).

You wouldn't be able to lock up the wheel with it, but it'd probably suffice pretty well for most normal rear braking... if you squeeze the lever hard enough!

You could even have two pinching the tyre, or better yet, one of those nice ones that rolls on the outer circumference.

I notice you didn't say 'could heat the spoon'; have you performed the experiment? :eek: :p

I agree. I use to ride and race in the mountains of Calif, and a lot of that riding temps would be over 95 degrees, combine that temp with road surface temps and braking coming down fast descents you have quite a heat situation, and yet I never blew a tire from heat. I have heard of the rare occurrence of tandem riders that happened to, but it was even more rarer for a single roadie to have that happen to. I was taught when I first started training and racing mountains was to brake hard for about 3 to 5 seconds then release for about 3 to 5 seconds, and even though that 3 to 5 seconds of release seems short the air rushing past the aluminum rim does cool the rim enough. It was called stab braking...semi trucks do the same technique for the same reason! Problem is with CF rims is that they don't cool down like aluminum so the heat just builds and builds to the point either the tire blows or on cheap CF generic rims the rim can delaminate.

I assume you'd need to have special tire sidewalls: as others have noted, a rubbing brake pad can damage a tire sidewall relatively quickly. Tire sidewalls are also one part of the bike that you definitely don't want to risk wearing through. Brake pads wear consistently and visibly, and the failure mode isn't likely to lead to a sudden loss of control: in the worst case you'll get some horrible noises and impaired braking performance, and should have a second brake to use. Whereas if breaking wears at the sidewall, you're risking a blowout and sudden loss of control

Isn't it just a consequence of the evolution of bike design? The wheel came first (and was designed to carry the bike, not to dissipate braking heat) so the brake pad was designed to act on the wheel as it then existed.

Sure, but these points can now be taken into consideration with a modern design, e.g. brake pad material with a high heat capacity (some early ones were wooden),larger brake pads, heat sink or cooling fins to dissipate heat.
Now that I like. I've been wondering about a way of harvesting braking energy, and that seems like a simple, workable method. Maybe it should be a new thread.

Hmmm, doesn't the Copenhagen Wheel use regenerative braking?

Yes, but it's estimated cost is $600.

Regeneratve braking is fine for long gradual braking, or speed control on descents, but not for hard braking and short stops. The size and weight of a motor that could provide that much torque is more than anyone would accept on a bicycle. Even hybrid cars that use R-braking still use traditional mechanical brakes for hard braking.

A great many ebike drive systems incorporate regenerative braking.

Or to look at it another way, the motor is going to be about as powerful braking as it is accelerating. But in fact you need and want to be able to stop much harder than you go. Also in the usual bicycle arrangement it's on the rear when you need the most braking power at the front.

Here one on my local C.L. right now

http://cosprings.craigslist.org/bar/4145184181.html

I never realized this until now, but it makes a ton of sense. Thank you!