On Sun, 19 Dec 2004 15:11:53 GMT, "(Pete Cresswell)" <[email hidden]>
Quoted message said:Subjectively, it feels to me like I'm working harder on a given hill when it's
cooler and my average ride speeds are down.
OTOH, it seems like I read somewhere that optimal body performance happens
somewhere in the mid fifties.
Also it seems like the colder the air, the denser the air - and the more O2 per
lungful....but it *feels* harder.
The extra clothing? My imagination?
Dear Pete,
It's not your imagination. Riders usually go slower as the
temperature drops for several reasons.
A) Temperature comfort--going slower reduces wind chill
B) Breathing comfort--cold air is denser, but much less fun
C) Clothing aerodynamics--winter clothes = wind drag
D) Raw wind drag--density affects drag more than breathing
The wind drag of the denser cold air is probably the biggest
factor.
http://www.kreuzotter.de/english/espeed.htm
Choose hands on the drops, take the defaults (such as 160
watts), and change the temperature from 81F to 36F--the
calculator above will predict a half-mile-per-hour drop from
19.6 to 19.1 mph:
To give a broader idea, here are the predicted break points
for the defaults:
19F 18.9 mph
27F 19.0 mph
36F 19.1 mph
44F 19.2 mph
53F 19.3 mph
62F 19.4 mph
71F 19.5 mph
81F 19.6 mph
90F 19.7 mph
At 19.6 mph on an 81F summer evening, my daily 15.2 mile
ride would take 46:32.
At 19.1 mph on a 36F winter afternoon, the same ride would
take 47:45, 73 more seconds, about a half-mile lag. (My
records show this kind of seasonal variation in speed with
depressing regularity.)
To raise the default rider's speed from 19.1 to 19.6 mph at
36F, the 160 watt power would have to rise to 172 watts, a
7.5% increase in effort, much more than would be expected by
any change in breathing due to air density.
For bicycles, any slight change in the air exaggerates wind
drag more than any other factor. By craftily raising the
altitude from the default 1150 feet to 5000 feet, the rider
can increase his 19.6 mph speed at 160 watts and 81F to 20.4
mph.
Carl Fogel