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Old 02-13-07, 10:09 AM
  #17  
Speedo
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Bikes: Univega Gran Turismo, Guerciotti, Bridgestone MB2, Bike Friday New World Tourist, Serotta Ti

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Originally Posted by dalmore
Try this physical experiment for yourself. Get up to speed on your bike using any means you desire. Without changing your front chainring, shift to your largest rear cog and gauge how much resistance you find on the pedal. Then while still at speed and again without changing your front chainring, shift to your smallest rear cog and gauge how much resistance you find on the pedal. There was more resistance when you were on the smaller cog yes?
Yes, you apply more torque, but at a lower rotation rate, so the power is the same. The energy you put into the bike is the same in either case. Your engine might run more efficiently at a particular torque/rate combination, so you will find you prefer a gear, but the energy you put in is the same in either case.

The wheel is a "lever" as you put it. It factors into the gear sense that you experience. That's why Gear Inches includes the diameter of the wheel. But don't confuse the mechanical advantage of gearing with where the energy goes when you put it into the bike.

Originally Posted by dalmore
As far as upgrades ... I for one can not magically reach 20 mph where the rotational mass of the tire become a flywheel and aerodynamic drag is my biggest enemy... I have to reach that 20 mph point first by exerting energy. And with the rolling terrain around here, I spend more time accelerating up hills than I do gliding down them in a tuck position. So for me, $400 on lighter wheels to get better acceleration might be a more cost effective upgrade than $30 on aero bars.
When you go up a hill you, the engine, are increasing your potential energy. Light wheels, being lighter, are easier to carry up the hill. But as you crank up the hill, even the little changes in speed from the crank pulses are a subtle dance between the energy you put in, the energy stored as translational, and rotational kinetic energy, friction and drag, and potential energy. The energy that goes into spinning up a wheel, you get back; it is conserved.

Look, I've always conceded that lighter is better. But the point is to understand what you are, and what you are not, buying. I'm someone who has bike priorities, and believes that money spent on bikes is money well spent. If you want to spend $400 ($500, $1000!) on wheels and your only reason is that they look cool and make you feel fast, that's a good enough reason in my book. If you have a set of modern alloy rim wheels, with good quality hubs then, upgrading for lightness is not going to dramatically improve your overall speed.

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