On Sat, 08 Sep 2007 13:10:34 +0100, Eiron wrote:

Don Pearce wrote:
On Sat, 08 Sep 2007 08:42:58 +0100, Eiron wrote:

Andre Jute wrote:

Those brakes aren't dodgy, Don, they're hyper-competent; what I forgot
to add is that they have a built-in modulator. They stop the one-
eighth of a ton of me and the bike and light touring gear from thirty
kph in 11 feet. I know, because I chewed up a pair of tyres while I
practiced that one to perfection. But I agree with you, for casual use
those roller brakes are overkill.
A fat man on a granny bike braking at over 1g!
Don't the laws of physics apply in Eire these days?

Quite so. That comes out at 1.05g. Centre of mass combined with
wheelbase tell us that he performed the last 8 feet of that stop flat
on his face in the road. But that is a perfectly legitimate way of
stopping your bike.

I just tried a normal stop from 20mph on decent tarmac. It took 12 yards
which averages 0.37g, and the back wheel was hopping about. I expect 0.5g
would be a reasonable maximum if I moved down and back, or a bit more if
I wasn't so fat. Perhaps André meant 11 yards, or perhaps he's just won
another thousand euros after betting that someone would point out the
deliberate error. :-)

I'd be very surprised if you could ever reach 0.5g on a pushbike,
unless it is a recumbent. You just sit too tall with respect to the
front wheel position. If your back wheel was hopping, you had reached
the limit, and it is really difficult to do anything but move your
body forwards under braking - there is nothing to brace against.

So maybe he did mean 11 yards, but that would be a shame because it
would mean those fancy brakes couldn't actually match a normal set.

d

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Pearce Consulting
http://www.pearce.uk.com