Tyre braking?
 

If you can use a rubber brake block on a metal rim, could you use a metal brake block on a rubber tyre?

Tyres wear and get replaced much more quickly than rims, so tyre wear from braking wouldn't be the issue it is on wheel rims.

Or just ram a stick through the wheel

It's called spoon brake, and it was done before in the early 1900's

http://upload.wikimedia.org/wikipedi..._Chainless.png
http://upload.wikimedia.org/wikipedi..._detail%29.jpg
http://upload.wikimedia.org/wikipedi..._variation.jpg

and homemade version:
http://upload.wikimedia.org/wikipedi.../Marian038.jpg

i have more confidence in the kids that use their shoe to stop the rear wheel...


:lol:

Hmmm. Kind of an interesting idea. You could have rubber brake tracks on the sides of the tire and have metal brake shoes in calipers. Perhaps the main problem would be that the brake travel and force would depend on tire pressure. There'd be no braking with a flat tire.

Why not just drag your feet along the ground? Because after all, your shoes get worn out anyway and your bike will be a lot lighter without any brakes at all.

That spoon brakes were once the standard and yet there was a search for better braking might suggest something. The few bikes that I've ridden with spoon brakes had EXTREMELY poor stopping performance. Andy.

Please don't confuse the electorate with logic or truth.

I don't. Read my second sentence. Andy.

Hmmm. Your post seemed to express both deductive logic and an empirical truth. Are you now saying it does not?

asi +1

Yes in the early days of cycling the brake rubbed right on the tread.

Btw on the subject of brakes, IMO the best way to go is disc brakes. That way the rims can be designed for maximum strength, and given a aero shape. Replacing pads or discs is very easy. Rim brakes wear out rims, and require an expensive rebuild. Most cyclist can replace their own discs and pads no problem.

The first bicycle brakes were exactly that way. A metal spoon pressed down on the tire at the fork crown. These were reasonably effective, but the spoons would heat up and wear very quickly.

The key to effective braking is to dissipate the heat that braking produces. Since rubber is a poor conductor, all the heat of braking will go to the metal part. Rims are a relatively large heat sink, and provide decent surface for heat transfer to the air. Reversing the arrangement, means that the small spoon cannot take up much heat and has little surface to transfer it to the air.

In all vehicular braking, the real issue isn't how to create friction but managing the heat produced. You see this on cars and trucks, where they direct air flow over discs, and in some cases use steel clad copper discs to conduce the hear away from the surface faster.

Good lord, spoon brakes. I hadn't thought about stopping with a flat...that must have been interesting.

The homemade one doesn't look TOO bad.

On the bright side, these are probably the easiest brakes to service :p

M.

[QUOTE=Asi;16193354]It's called spoon brake, and it was done before in the early 1900's

"The spoon brake, or plunger brake was probably the first type of bicycle brake and precedes the pneumatic tyre" (1) [and was therefore not designed to work with one].

"Though made obsolete by the introduction of the duck brake, coaster brake, and rod brake, spoon brakes continued to be used in the West supplementally on adult bicycles until the 1930s, and on children's bicycles until the 1950s. In the developing world, they were manufactured until much more recently".(2) So they can't be that bad, can they?

Plus, you have to compare like with like. A valid comparison to those spoon brakes pictured would be a rod-actuated caliper brake from the same era. A present-day design (working on a tyre designed to use it) would be nothing like a spoon brake.

Of course it wouldn't work with a flat tyre, but you can't ride the bike with a flat tyre. Come to that, you could say the same thing about most of the components on the bike (don't work well when incorrectly maintained or adjusted).


1. Bicycling Science (2nd ed.), pp.153–154
2. http://en.wikipedia.org/wiki/Bicycle_brake#Spoon_brakes

[QUOTE=TimEarl;16193796]
The only real problem with spoon brakes is the lack of heat capacity. Otherwise they're fine. They're still OK for children's bikes, and for utility bikes in relatively flat areas, but the limited heat capacity is what makes them unsuited for today's faster speeds, or for use in hilly terrain.

A modern bike on a long downhill can heat the spoon until it's red hot and simply melts apart.

Tim, I don't think comparing rod-brakes and spoon brakes is valid either, as rod brakes from the era were rim engaging.

As for heat capacity, FB that sounds borderline awesome and terrifying.

I guess these could work with pneumatics if you had a "warning layer" between the thread and the tread in like yellow to tell you when you're just about ground through your tyre.

M.

With spoon brakes, the steel spoon wears faster than the tire. The tire picks up abrasive media (grit) from the road and uses that to destroy the spoon. Also consider the difference in working area, 3 inches of spoon vs. 80" of tire.

Anyway most tires do have wear indicators in the form of a clear or tan gum layer between the tread rubber and tire cords. Even when they don't, the lighter cords show up in good conrast long before they're actually compromised.

Interestingly, I found a stationary bike in a thrift store this morning that used a spoon brake sort of thing to adjust the resistance.

Sorry, I read into your reply that I was giving the elecorate too much credit. Andy.

Ah, that all makes sense.

M.

But it is quite likely that you'd want to be able to safely stop the bike when you do get a flat...

A better question is what happens if your brake pads work against your tire sidewall. Doesn't take long to wear completely through the tire and cause a blow out.

That's true. Maladjusted brake pads eat sidewalls quick.

M.

My brother when he was 12 or 13 once tried using a large plastic bag as a drag chute on a bike, he simply held it up over his head at about 10mph open the bag and was blown off his seat! He did stop, but I couldn't stop laughing.

Fb, you might find this interesting-re heat dissipation, a pretty cool example of this (sic) is with European truck racing, race versions of 18 wheeler cabs that are raced on all the famous circuits (donington park in England for example). These are big heavy vehicles and they use ( or at least used to, I haven't seem them for years) a water cooling system on the front brakes ( huge disks I assume) so when coming to a braking point, large clouds of steam pour out from the front. First time seeing a race produced a proper wtf?from me. Strange looking yet effective way to disperse heat. YouTube it if curious.

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.