On May 13, 3:05 pm, Robert Chung <
[email protected]> wrote:
> On May 13, 5:55 am, Andre Jute <[email protected]> wrote:
>
> > > FWIW, we've been discussing this, and another, method over on the
> > > Wattage List.
>
> > Perhaps it will be useful if you were to describe the two methods, and
> > give us a summary of the consensus, if any, and remaining
> > difficulties, perceived or real.
>
> We've actually been discussing more than two field methods, though
> each of the ones we've been discussing require that power and speed be
> known using an on-bike power meter.
That's the necessity my method is intended to circumvent. The common
coastdown method takes a spot reading on some maximum speed and,
generally speaking, derives both power and Cd from there, a procedure
with considerable potential for error.
> OTOH, I'm still fascinated by your method which requires nothing more
> than a bike and the road on which to ride it. Perhaps it will be
> useful if you were to describe what you meant by "a very high degree
> of accuracy"
I certainly don't mean 2% repeatable. I mean a very high degree of
accuracy relative to the spot method, all other conditions holding. My
purpose is a useful reading to a particular cyclist on his own roads,
under his own conditions, without presuming expensive instrumentation.
I deduce that it will be more accurate than the spot reading on
coastdown method because of the internal structure of my method, which
calculates the cyclist's power by arguing that he outputs maximum
power not only at a maximum speed but on acceleration, and then takes
repeated acceleration readings and averages them, thus reducing
measurement error progressively, and also averaging uncontrolled
factors over time. Note that my formulation has an as yet undeclared
internal check by which total tractive effort must equal total
tractive resistance; this is illustrated in the graphic on p162 of my
book from which I adapted these methods (Andre Jute: Designing and
Building Special Cars, published by B T Batsford, London, 1985,
published in the States by Robert Bentley of Boston).
>and give us a summary of the consensus, if any, on your
> method?
It's a newly formulated method for cycling; by the nature of people's
attitudes to the novel, I would expect zero consensus from the stick
in the muds and growing consensus over time from those with enquiring
minds and the engineers who either have an automobile (or possibly
railway) background or are the possessors of better brains so that
they can follow the logic which, I admit, I haven't laid out as fully
as in my book. I was in fact pleasantly surprised to hear people
instantly agree that the formulae are correct and state that their
reservations are about applicability to cycling. However, in
automobiles, the consensus is 100%; these are methods proven by time,
taught to first-year mechanical engineering students, generic to every
comprehensive textbook. Special car builders write to me to express
their delight at how easy it is once the method is understood, and
expressing surprise too at how consistent the results are with
expectations and the experience of others "in the club".
>Can you provide an example from data you've collected using
> your method?
It's a new formulation for cyclists, so I have no data on cyclists
yet, and my data on automobiles by which I tested my formulations for
(uninstrumented) special cars builders was published in my book cited
above, where you can look it up.
HTH.
If you're a young fit, preferably slender, cyclist with a friend or
two to help in these tests, perhaps you should start collecting data
to see how well my method works. It is described here:
http://members.lycos.co.uk/fiultra/BICYCLE TECH -- basic cycling parameters.html
and aspects of methodology re recording are discussed in this thread,
and Rik O'Shea also in this thread has provided a more rigorous test
protocol than I laid down -- I'm happy with a pretty casual approach
as long as casual doesn't become slack, and as long as the test
iterations mount up inexhorably.
Andre Jute
http://members.lycos.co.uk/fiultra/BICYCLE & CYCLING.html
