Quoted message said:Quoted message said:On Jun 23, 10:35 pm, [email hidden] wrote:
Quoted message said:Quoted message said:If you had to guess, which ride(s) would you guess--
Quoted message said:Quoted message said:Er, which ride(s) would you predict had 7 pounds of steel rods added
to the top tube of a ~27 pound bicycle with a ~193 pound rider?
Quoted message said:Well that depends. If your 15-mile ride included a climb to the top of
Hardscrabble Pass, I'd boldly predict that your slow times correspond
to hauling 8 pounds of extra weight. But I know you like to cruise the
endless flat expanses around Pueblo and thus there is no way to
predict without knowing the wind speed and direction each day, as that
would be the most important variable affecting your average speed.
There's a reason that big riders struggle on the hills.
Quoted message said:Robert
Dear Robert,
Well, my daily ride is flat for values that include the 400-foot climb
up the ridge west of town.
This year, my average top speed coming back down the ridge is 39.03
mph, varying from 48.7 mph to 32.1 mph, a sizeable variation that
illustrates your point about wind even on downhills.
In fact, even minor wind variation matters more than weight on the
uphill on Hardscrabble.
Hard to believe, but read on.
If you mean Hardscrabble Creek from Wetmore (about 30 miles past where
I turn around on highway 96), that's a 3.4% grade of about 16 miles:
http://www.rmccrides.com/ClimbDB/climb_detail_page.php?climb=146
So let's look into 16 miles up a 3.4% grade, 193-lb rider with 27 and
34 pound bikes at 7500 feet, (bottom is 6100, top is 9085), clinchers,
on-the-drops:, 200 watts (hey, it's a round number):
http://bikecalculator.com/veloUS.html
27 34
up 93.80 96.24 heavy bike 2.44 minutes slower (2m:26.4s)
But now make the rider climb into a gentle 5 mph headwind:
27 34
up 100.09 102.46 heavy bike only 2.35 minutes slower
That modest 5 mph headwind adds about 6 minutes to the climb time for
either bike. (The heavy bike actually closes the gap a little.)
So a 5 mph headwind makes a bigger difference on the climb than adding
7 pounds to the bike.
On a still day with no headwind, the heavy bike reaches the top of
Hardscrabble in 96.24 minutes.
On a day with a 5 mph headwind, the light bike takes almost 4 more
minutes to struggle to the top at 100.09.
They're going 9~10 mph in all cases.
Cheers,
Carl Fogel
Carl:
A couple of things are missing.
1. The whole rotating mass bit, which fuels probably the largest,
highest $ growth part of the high end bicycle market--getting people
to put on light, fragile wheels, and lighter pedals. But, light wheels
are where there's more money, as they fuel the demand for light tires
of ever changing colors.
2. Nobody demanded you convert some of your duration metrics to
distance when the sprint setting you posed pretty well begged for it.
And from the outset, you obliterated differences in acceleration by
swamping them in steady-state durations. Which, to be fair, would be
like pointing out that a 50% cure rate for a rare disease has
negligible impact on overall mortality. If Consumer Reports (CR) has
delivered 0-60 and 50-65 acceleration times, CF should have cranked
out estimates of acceleration parameters. The hyperbolic feature
article you ridicule is, after all, about claimed sensation of
acceleration improvements.
(A general observation about weight and bicycles. Present a fancy
racing-inspired bicycle to 100 civilians, something that LOOKS fast,
and as long as it weighs under, say 22 lb and looks light, the second
thing the civilian, man or woman, will do to judge and admire it will
be to lift it by the saddle and marvel at how light it is. After
looks, what else do they have to go by? Half of them can't ride, and
98% don't. So they admire the looks, then lift it from the saddle and
pronounce it light ....and good. And which of two is better, and must
be faster, if they want to or wish to compare them? The one that is
perceptibly lighter.
Readers here, including skeptics, may approach a quality bike from the
left, lift it by the saddle, and be disappointed that it seems heavy.
Maybe because of junk in the trunk, heavier cog set, heavier tire.
Whatever the cause for the surprise, it is in the direction of
disappointment.)
Now #1, above. I'm surprised nobody demanded to know where you assumed
the mass was distributed on the bikes, especially in your example of
the sprint. I doubt slightly lighter wheels are perceptibly faster,
but that's what and why marketers are pushing seriously lighter ones.
#2. In the case of the sprint, and assuming you modeled with all the
weight on frame, the .4 seconds difference in finish time translates
to 6 to 8 meters at the finish. Put the weight on the wheels and it
would be more. That's quite a bit, and you posed that competitive race/
place situation yourself,
Also there may be more to acceleration perception than you have
credited, which is why crazy light and fragile wheels MAY be
perceptibly faster. Automotive engineers design accelerator pedals and
linkages to maximize the perception of acceleration in response to
foot movement on the pedal. That's independent of and having no effect
on any part of the fuel/air feed, the transmission, or engine. Just
the pedal and linkage.
That said: I ride with just a few lb less patch and repair than you
do, can't see myself riding wheels with fewer than 28 spokes, and
wonder about people who keep riding on and complaining about bicycle
tires that are thin and light enough to have them flatting on 5+% of
their rides. And, if such wheels were not so robust I won't need more,
I would worry about the supply of 2kg pairs of "Jobst's wheels" on
the used market.
Harry Travis
