Buck <j u n k m a i l @ g a l a x y c o r p . c o m> writes:
> What you are ignoring is the fact that you have two lumps of flesh and bone pumping up an down and
> two somewhat smaller lumps moving around in circles. It takes energy to move these. The more times
> they have to be moved, the greater the energy output. Note that this all happens *before* we start
> talking about forces on pedals and forces moving the system as a whole.
That is not why it is strenuous. Just pumping a muscle back and forth doing no work at all requires
power as you can prove by riding an exercise bicycle with load set to zero. Power required to do
work goes above and beyond that effort, so it is an optimization between excess idle work and
output. That cadence is different for each individual and depends on several factors, such as
weight, muscular strength (not power), cardiovascular capacity and conversion of glucose to the
muscles... and a bunch of other things.
> Take, for another example, big trucks. When the speed limit changed to 55, the cost of overland
> transportation went up. Not just because of additional time needed for transportation. The trucks
> were designed to cruise at 70mph and were most fuel efficient at that speed. Lowering the speed
> limit forced them to drive at a speed that wasn't as fuel efficient. Their fuel costs went up
> because of inefficiency and more time spent on the road.
The cost is driver time (labor) and turn-around time for equipment, not fuel efficiency. Wind drag
power goes as the third power of velocity and that is twice as great for 70mph as at 55mph. Rolling
resistance is essentially constant at those speeds. This is not a good argument for spinning or not
on a bicycle.
> If you take issue with this, consider the Continuously Variable Transmission. In a vehicle that
> uses a CVT, the engine speed varies only between idle and a pre-set optimum rpm. Why? Because
> "keeping the engine at a constant rpm allows the engineers to optimise ignition timing, camshaft
> design, and manifold tuning for excellent volumetric efficiency and low emissions."
http://www.canadiandriver.com/articles/jk/at_010508.htm
I don't think you should bring the CVT in on this because the web page you cite is full of erroneous
information. If what is presented there were true, we would not have gearboxes on cars and trucks,
from Formula One race cars to heavy trucks. The CVT is NOT more efficient. It has its place and
trying to push it into applications where it doesn't fir is a disservice to the device.
> The beauty of a bicycle with gears is that the rider can find the optimum cadence and maintain
> that cadence through a wide range of speeds. Every system has an optimum performance range,
> whether the system is mechanical or biological. Ignoring this is ignoring the physics you love.
That's an old saw that just isn't true. You will notice that even professional racers slow their
cadence as the gradient gets steeper. In the extreme, the race up Fillmore Street in San Francisco
made that glaringly apparent. There are reasons for lower cadence on steep hills and I don't think
we want to get into that here.
By the way, where is the CVT for bicycles?
Jobst Brandt
[email protected] Palo Alto CA