J
John Dacey
Guest
On Fri, 03 Jun 2005 00:30:40 -0600, [email protected] wrote:
>A current thread debating the desirability of a rear brake
>on a fixie led me to wonder just how much effort is involved
>in slowing a fixie down by just fighting the pedals (no hand
>brakes).
<snip>
>A few questions . . .
>
>First, does it seem reasonable that the rider would have to
>put out around 300 watts of resistance to slow his gravity
>propelled descent from around 32-39 mph down to around 20-23
>mph?
>
>That seems like a lot, but the numbers don't seem to add up.
>
>If it takes 952 watts to go 33.4 mph on the flats, and only
>233 watts to go 20.0 mph on the flats, the difference would
>seem to be around 720 watts, not the -299 that may be
>fooling the calculator.
>
>Next, why do all the calculators accept negative numbers up
>to around the same point (294 to 332 watts) and then choke,
>showing Nan, 0 mph, or confused exponential notation? Were
>these programmers so blinded by anti-fixie prejudice that
>they failed to consider this crucial situation?
>
>Finally, how much anti-pedal effort should it really take to
>slow a fixie from around 30 mph to around 20 mph on a steady
>7% grade? Much less than the roughly 300 watts predicted by
>these sadly abused calculators? About 300 watts? Much more?
>
>Curiously,
>
>Carl Fogel
No! no arresting the vast wheel of time,
That round and round still turns with onward might,
Stern, dragging thousands to the dreaded night
Of an unknown hereafter.
- Charles Cowden Clarke
You seek an answer to a question that has no practical application.
Even with a 90 inch gear (which exceeds by far what would commonly be
used by fixed-gear road riders), at 39 mph the cranks would be
spinning at a rate such that no rider would be able to effectively
apply meaningful back-pressure to the pedals. The best for which one
could hope would be to sit up and let aero drag attenuate some speed.
Even at 30 mph, the pedal cadence will be such that, on a 7% grade,
the bike would probably regain as much speed in the intervals between
back-pedalling efforts as you could slow the bike with those efforts.
After fatigue sets in after a few futile attempts to arrest the bike,
you'd be back to careering downhill at a rate limited only by the
slope and aerodynamics.
-------------------------------
John Dacey
Business Cycles, Miami, Florida
Since 1983
Comprehensive catalogue of track equipment: online since 1996.
http://www.businesscycles.com
>A current thread debating the desirability of a rear brake
>on a fixie led me to wonder just how much effort is involved
>in slowing a fixie down by just fighting the pedals (no hand
>brakes).
<snip>
>A few questions . . .
>
>First, does it seem reasonable that the rider would have to
>put out around 300 watts of resistance to slow his gravity
>propelled descent from around 32-39 mph down to around 20-23
>mph?
>
>That seems like a lot, but the numbers don't seem to add up.
>
>If it takes 952 watts to go 33.4 mph on the flats, and only
>233 watts to go 20.0 mph on the flats, the difference would
>seem to be around 720 watts, not the -299 that may be
>fooling the calculator.
>
>Next, why do all the calculators accept negative numbers up
>to around the same point (294 to 332 watts) and then choke,
>showing Nan, 0 mph, or confused exponential notation? Were
>these programmers so blinded by anti-fixie prejudice that
>they failed to consider this crucial situation?
>
>Finally, how much anti-pedal effort should it really take to
>slow a fixie from around 30 mph to around 20 mph on a steady
>7% grade? Much less than the roughly 300 watts predicted by
>these sadly abused calculators? About 300 watts? Much more?
>
>Curiously,
>
>Carl Fogel
No! no arresting the vast wheel of time,
That round and round still turns with onward might,
Stern, dragging thousands to the dreaded night
Of an unknown hereafter.
- Charles Cowden Clarke
You seek an answer to a question that has no practical application.
Even with a 90 inch gear (which exceeds by far what would commonly be
used by fixed-gear road riders), at 39 mph the cranks would be
spinning at a rate such that no rider would be able to effectively
apply meaningful back-pressure to the pedals. The best for which one
could hope would be to sit up and let aero drag attenuate some speed.
Even at 30 mph, the pedal cadence will be such that, on a 7% grade,
the bike would probably regain as much speed in the intervals between
back-pedalling efforts as you could slow the bike with those efforts.
After fatigue sets in after a few futile attempts to arrest the bike,
you'd be back to careering downhill at a rate limited only by the
slope and aerodynamics.
-------------------------------
John Dacey
Business Cycles, Miami, Florida
Since 1983
Comprehensive catalogue of track equipment: online since 1996.
http://www.businesscycles.com
