[email protected] <
[email protected]> wrote:
> On May 10, 12:47 am, Andre Jute <[email protected]> wrote:
> > Yo, Joseph, as I promised, I have published an article showing how a
> > cyclist can discover his power output and Cd with no tools except his
> > bike and a road, yet with a very high degree of accuracy. See http://members.lycos.co.uk/fiultra/BICYCLE TECH -- basic cycl...
> >
> > HTH.
> >
> > Andre Jute
> > http://members.lycos.co.uk/fiultra/BICYCLE & CYCLING.html
>
> Cyclist power is highly irregular. Chis Hoy powering to a world record
> standing start kilometer puts out way more power than he could out
> training on some long hill climb. He probably doesn't care what his
> sustainable aerobic power is, likewise Leonardo Piepoli probably
> doesn't care what his stanidng start power is. Muscle strength,
> gearing, and a whole bunch of other factors make an acceleration test
> for cyclists problematic.
The method I'm suggesting is exceedingly subtle, so it takes a while
to understand how it overcomes all these difficulties you raise. My
method uses repeated surplus traction measurements over your speed
range (that's those iterative acceleration readings) to measure very
closely your power *on the day*, and then, without any assumptions or
manufactured constants -- fudge factors, guesses, kludges --
approximates very closely all the other factors lumped together that
influences Cd (that's the coastdown tests) to determine your Cd.
This business of adjusting constants -- fudge factors, guestimates,
street myths, wishful thinking -- is important. Notice for instance
that I made -- it took me two days of hard thought to get there -- a
formula that entirely obviates the necessity for working with the
rolling resistance of some notional tire because I saw too wide a
range in the data you referred me to, and didn't trust the idea of a
lab test with a drum substituting for the road. Instead, I made my
formula include the actual tyres you use on the test, with a real
measurement, not a guesstimate, no matter how distinguished the
guesser. In fact, I made my formula work so that it can operate as a
check on the Cr guess!
But if you think my suggestion is too much work, then that's it;
someone else will take it up sooner or later and then we'll find out
who's right. All I can say is that my method has worked for a quarter-
century for special car builders who bought my book (they write to me
to tell me so) and before that, back into the nineteenth century, for
automobile engineers and before them railway engineers, whose methods
I adapted in the light of modern requirements and knowledge. (It isn't
like I invented anything weird: I just rearranged and reapplied widely
known physics to overcome practical difficulties in cyclist
measurements.)
> Perhaps a more suitable way would be to use a hill of known slope and
> coast down from a standing start, and measure elapsed time and if
> possible speed at the end of the course.
Sure, if that's what you want to do. It sounds a lot easier and
quicker than my method, but it only gets you one reading; even
averaging several runs gets you only one data-point (my suggestion
gets you averages on many data points -- you could for instance use
the data gathered for my method to calculate your optimum gearset). To
exclude the other factors from your reading of downhill speed to
arrive at Cd, you must then have instruments not available to you, or
make all kinds of assumptions about conditions and mechanical
reactions. My method, while more tedious, excludes these sources of
error.
> That way you get to use the nice and consistent gravitational force
> instead of the variable pedal power.
The second, coastdown part of my suggested test also uses
gravitational force. The iterative acceleration tests overcomes the
perceived problem of variable pedal power. You keep trying to solve
the problem with one big bang, by measuring top speed and trying to
deduce power from that; that is obviously a very fallible method. My
method argues that you exhibit maximum power on acceleration, and by
repeated tests over various ranges with results averaged, it will give
a more reliable final reading. What's more, my method separates the
distribution of the power between the resistances without making any
assumptions and without any fudge factors.
> I have a constant slope hill with a clear 300m or so that would be
> good for such a test. I just don't know what to do with the info I
> could gather there.
Graham has already supplied a formula
We'll find out after you do the downhill test whether the Cd you
calculate predicts your maximum speed pedaling flat out along a flat
road, which is the point of having a Cd number. One thing is for sure:
if you merely want a cafe Cd closer to the 0.3 you dream of than the
c0.5 average (for 80 per cent of racing cyclists, say) that I suspect,
you're more likely to have your wish fulfilled with the downhill
shortcut than my method!
For those who want to look it up, we're referring to my article at:
http://members.lycos.co.uk/fiultra/BICYCLE TECH -- basic cycling parameters.html
Good luck with the test.
Andre Jute
No such thing as a free lunch -- Hayek
Never ate lunch in my life -- Armstrong
