Some old rod-brake roadsters (dutch bikes) had brakes sort of like this,
that pushed on the tyre. If you value your life, never borrow one of
these bikes off anyone. They're terrible. You're not going to get
progressive braking by pushing against something that is deformable
(the tyre), the tyre pushes in when you brake and does weirdy stuff.
You get extra tyre wear and if you're riding in the rain the brake bit
can grab stuff off the tyre and push it in, causing a puncture.
What advantage does it have over a normal brake, it seems more complex,
with the variable resistance bit, and relies on a bunch of custom parts
rather than just off the shelf bike bits. Also, the simplicity relies a
bit on the lever coming out somewhere nice to hold, or else you're
going to need to extend that with another part going up high enough to
grab on. It also looks like being quite big and heavy, you're going to
have to build those levers quite strong to make them not bend when
you're pulling sideways on them all the time, and when all the braking
force is transmitted into sideways force on the lever.
The other problem is that I think from your diagram, resistance to the
roller spinning will cause the front of the lever to move upwards,
pushing the brake on harder, and presumably making the resistance
change? Like when you have a v-brake setup that isn't toed in, and it
just goes on very suddenly, because the braking action causes the brake
to turn on.
I think tyre crossection and bumpyness is likely to make a difference
even on a smooth tyre, on a rim brake you can notice tiny rim
differences, which are far smaller than the kind of bumps you'll get in
a tyre, especially one that you've worn down unevenly, as is often the
case on unicycles.
What problem is it designed to fix?
Joe
--
joemarshall
my pics http://gallery.unicyclist.com/albuq44
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