experience of the dahon roo el

Simon Brooke

in message <347gi9F45ajinU1@individual.net>, Peter Clinch
('p.j.clinch@dundee.ac.uk') wrote:

> Simon Brooke wrote:
>
>> And
>> the bike looks as if it would reasonable to cycle, for short distance
>> urban trips (which is all an electric bike is ever going to be
>> suitable for anyway).
>
> The owner of the Heinzman and Rohloff equipped Grasshopper built to
> order by Darth Ben may well have issues with that particular
> comment...
>
>> The power and range of any electric assist bike is poor, as compared
>> to any other vehicle on the road and particularly as compared to an
>> unassisted bike; they are a classic illustration of the truism that
>> the lazy man does the most work.
>
> Think you need to get up to speed with what you can do by spending an
> appropriate amount of money. I don't particularly have any need or
> want of one, but Heinzman equipped bikes with good batteries have high
> potential for utility in at least some situations. Have you ever
> tried one?

No, but the physics of it are fairly clear. The batteries have finite
energy density, the motor has finite weight and, when not running, adds
a certain amount of transmission drag (unless it can be entirely
decoupled - the SRAM unit can't, and neither can the front hub motor
things like the Heinzman). So when the battery is exhausted you have a
bike which is both heavier and less efficient than a similar but
unassisted bike. So what you are left with is a tradeoff between more
battery (last longer but when it gives out it's _even_ harder work) or
less battery (gives out sooner).

Or, of course, much more expensive battery. But however big or heavy the
battery, sooner or later it gives out, and then you have to lug it and
the motor the rest of the way by muscle-power - unless, as I say, you
limit yourself short distance urban trips.

If you look at Kinetics site you'll see the all up quoted weight for a
Heinzman-equipped bike including batteries is a staggering (and I mean
that literally) 28Kgs. You really, really would not want to have to
pedal that thing once the battery had died. So I stand by what I've
been saying: unless you're using them for very short distance urban
trips, these things are going to be much harder work over all than an
unassisted bike.

The Dahon Roo mentioned in the title uses the fairly light (2.5Kg
including epicyclic) SRAM unit and a fairly small battery, and has a
reasonable riding position. So it's not going to give much assist for
very long but it's not going to be a total joke when the battery has
run out. But it's still not going to be as easy or as pleasant to cycle
as it would be without the motor.

--
simon@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/

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