38 rear gear with a 20 front gear - Page 3

Tom Sherman <tsherman@qconline.com> wrote in message news:<c2p2g6$1vugr8$1@ID-81487.news.uni-berlin.de>...
> Carl Fogel wrote:
>
> > ... At the even more extreme ratio of a 20 front x 50
> > rear, your foot actually moves farther than the rear
> > wheel rolls. The ratio is 0.77, meaning that for every
> > foot that you crank the pedal, the rear wheel moves only
> > about 9 inches.
> >
> > You'd probably find it easier and faster to walk next to
> > the bike than to use such an extreme ratio. Its only use
> > will be if your leg problems are so bad that you can't
> > walk up the slope.
> >
> > Even then, balance would present a problem. It's hard
> > enough to balance a smoothly pedalled bike heading
> > uphill at such low gearing. An uneven power stroke would
> > make balancing even more difficult....
>
> Dear Carl,
>
> The obvious solution is to add a third wheel. For example,
> an 11-34 cassette and a SRAM Dual Drive hub on a 406-mm
> wheel combined with a 44-32-22 MTB crank on a trike would
> have a gear range of 9 to 106 gear inches, or 2.2 mph at
> 80 rpm in low gear. This would allow an average rider to
> pull a heavy load up almost any hill found on paved roads.
>
> Tom Sherman - Quad Cities (Illinois Side)

Dear Tom,

For pulling a heavy load in addition to the rider, a
dreadfully low-geared tricycle should work as you suggest,
but I suspect that for the ordinary rider the problem is
that pedalling is not free.

At only 2.2 miles per hour, 80 rpm is an awful lot of leg-
thrashing. While the tricycle would offer balance, it
might still be easier to walk up the hill with a normal
stride, pushing the bike or trike, instead of doing just
as much work, plus all that extra high-speed leg raising
and lowering.

What I'm thinking of here is the difference between
pedalling yourself up a geared track next to a stairway
and just climbing the steps. Past a certain steepness,
gearing is unlikely to offer any mechanical advantage over
normal climbing.

The original poster's bad leg may not really change the
situation--80 rpm at 2.2 mph might be easier or not,
depending on the problem. If half the pedal cycle has
scarcely any power on it, then rapid pedalling might be
just as bad as slow walking.

Unfortunately, there may not be any good leg-powered
solutions for a rider with a bad leg on a steep climb.

Carl Fogel