Laying down the bike crap

 Who made this up? A bike will stop faster on it's rubber tires than
laying on a chrome exhaust pipe. Chrome slides on tar like a sled in snow.

 Broderick Crawford ililililil wrote:

Probably the same people who made up "never touch the front brake, it
will flip the bike right over".

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--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

 

Gordon Jennings investigated this claim in a Cycle magazine article in
1971 and he calculated that a rider *could* lock up a front drum brake
and be flipped over the handlebars *if* the brake lining material had
sufficient friction.

It seems that drum brakes have a self-energizing effect on the leading
shoe that assists brake lever pressure. Jennings said that if the
lining material was soft enough, all the rider had to do was touch the
lever and the brake would lock up and would not unlock.

 :-/ wrote:

They can be easily designed to be self-actuating, but it's not innate
in their design.  I've not owned a motorcycle with a front drum so
can't say from first hand information how the fronts are typically
designed.

In any case, did typical street tires available in 1971 have
sufficient friction to allow a "stoppie"?  (and before anybody starts
going on about drag slicks and other racing tires, note the word
"street").

A more likely outcome would be the front wheel sliding, which would
put you down but not pitch you over the bars.

--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

 

Yes, the self-energizing effect is innate in the design of drum
brakes. There are single leading shoe brakes and twin-leading shoe
brakes.

The brake shoe is actuated by a cam that is turned by the brake lever
on the backing plate. The brake shoe pivots on a fixed pin.

In the single-leading shoe design, tangential friction of the rotating
drum multiplies the force of the leading shoe against the drum as the
drum rotates.

However, the trailing shoe gets kicked away from the drum and does
little for braking. If you disassemble a single leading shoe brake,
you will see that one shoe is worn more than the other shoe, because
the front shoe does 90% of the braking.

Jennings calculated that 58 pounds of static force applied to the
leading shoe resulted in only 25 pounds in the trailing shoe and that
the dual leading shoe brake provided 80% more stopping force.


Tires don't matter. A 1971 CB750 had such a high center of gravity
it would stoppie at only 3/4 of a g of deceleration.