John Forrest Tomlinson said:Quoted message said:Alas, the calculators predict that Joe was yet another victim of
weight-weenie wishful thinking--surely you should be able to feel the
difference when you start pushing the pedals of a bike 1/3 lighter!
You might not be able to feel the difference in speed (though 3% is
conceivably noticeble), but you surely can feel some difference
(perhaps it's handling, perhaps it's stability/instaility).
Funny that a difference that large in bike weight is derided as
weigh-weeniness. Funny that 3% in time is considered weeniness.
Dear Carl. Please place a six pound piece of lead on your bike and
leave it there for the next year or so.
Cheers,
JT
Dear John,
Joe explicitly talked about "forward thrust" and "cruising speed," not
stability or handling, neither of which are likely to be noticeable on
a 92-mile Ride-the-Rockies tour on the highway--pavement posted at 65
mph doesn't usually highlight subtle handling improvements.
What time difference would you predict adding seven pounds to my
current ~220 pound bicycle-and-rider combination (steel with frame
bag, seat bag, and camera bag) would make at my average speed on a
daily 15-mile ride, which is back down to just under 50 minutes after
illness?
Would the improvement in my "forward thrust" be "noticeably robust"
without a stop watch? It's a tiny 0.5 km/h for a smaller rider on a 6%
grade?
Would I start "cruising at a more-than-respectable" clip? The
improvement is less than a practically unmeasurable 0.1 km/h on the
flats.
Let's see . . .
First, let's pretend that it's a flat ride, ignoring that 400-foot
ridge west of town.
15.1 miles = 24.35 km
24.35 km / (5/6 hour) = 29.22 km/h
190 lb rider = 86.4 kg
5,000 feet = 1523 meters
25 lb bike = 11.4 kg
32 lb bike = 14.5 kg
A sizzling 138 watts predicts the desired 29.2 km/h for the 86.4 kg
rider and 11.4 kg bike on this side-by-side calculator:
http://bikecalculator.com/veloMetricNum.html
Raising the bike weight seven pounds to 14.5 kg lowers the speed from
29.25 km/h to 29.14 km/h, 0.11 km/h slower.
It takes an extra 2 kcal.
Time rises from 49.95 to 50.14 minutes, 0.19 minutes. That's 11.4
seconds on a 3,000 second ride.
In other words, you'd need a lot of rides, a stopwatch, and a big
spreadsheet to show the difference in real life. (My daily time varies
considerably more than 11.4 seconds because of the wind.)
No human being can detect that difference without instruments.
It's a good example of how we pursue real improvements that are too
small to measure outside of laboratory-control conditions.
In real life, the lighter bike should indeed be ever-so-slightly
faster. But real life variables like wind, temperature, barometric
pressure, tire inflation, and what you ate for breakfast yesterday
will swamp that tiny improvement--we're kidding ourselves when we
think that we can "feel" a bike cruising 0.11 km/h faster at 29 km/h.
Joe was riding an unfamiliar 92-mile stretch of mountain highway with
plenty of encouragement and even pressure to believe that there was a
"robust" improvement in how fast he could go.
Limit the test to a 6% grade and you'll get a bigger difference, but
it's still too small for a human being riding on his own on an
unfamiliar stretch of highway to detect, even with a good cyclometer.
You're grinding 13.5 km/h up this new road on a 92-mile ride. You
don't know whether someone has put 7 pounds of lead weights in your
bike's frame.
Are you going faster or slower? The lead weights will change your
speed, one way or the other, only 0.5 km/h.
If you know that you're riding an $8500 bike that's 7 pounds lighter,
you're likely to believe that you're going much faster.
I'm sure that Joe "felt" the speed differences, but adding or removing
7 pounds doesn't make a difference that anyone can detect on that
92-mile ride with the seat of his pants. It takes a stopwatch and
plenty of tests to tease that kind of tiny speed difference out of
real rides.
Cheers,
Carl Fogel