Weight Weenie calculation
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Weight Weenie calculation
Contemplating upgrading shoes to save 200g,
& started thinking about what that would mean in terms of effort saved.
Does this make any sense?
- Ignoring smaller factors, Effort is saved from lifting less weight from bottom of pedal stroke to top of pedal stroke
- Crank length is equivalent to one stair riser, so one RPM= raising 200g one riser
- Flight of stairs~fifteen risers, so one RPM= raise 200g .0666/flight of stairs
- Ave. RPM=78, figure pedaling 3/4 of time (more?), so effective 58 RPM
- 58*.0666= 3.86 flights of stairs/min raising 200g
- Bodyweight= 74kg. 200g=.0027/bodyweight
- 3.86*.0027*60min.=.625 flights stairs climbed per hour
- So over 5 hr ride, heavier shoes is equivalent to climbing 3.13 flights of stairs extra work.
& started thinking about what that would mean in terms of effort saved.
Does this make any sense?
- Ignoring smaller factors, Effort is saved from lifting less weight from bottom of pedal stroke to top of pedal stroke
- Crank length is equivalent to one stair riser, so one RPM= raising 200g one riser
- Flight of stairs~fifteen risers, so one RPM= raise 200g .0666/flight of stairs
- Ave. RPM=78, figure pedaling 3/4 of time (more?), so effective 58 RPM
- 58*.0666= 3.86 flights of stairs/min raising 200g
- Bodyweight= 74kg. 200g=.0027/bodyweight
- 3.86*.0027*60min.=.625 flights stairs climbed per hour
- So over 5 hr ride, heavier shoes is equivalent to climbing 3.13 flights of stairs extra work.
#7
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Unlike being on-foot, the heavier shoe contributes usable power to the downstroke. For steadily cruising on a flat, I wouldn't be surprised if shoe weight has negligible impact, although it will certainly affect acceleration and climbing.
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Are you lifting the shoe with your right leg, or does pushing the pedal down with your left leg raise the right shoe without having to fight gravity for those 200g?
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I made a remark in an earlier thread, referencing the fact that serious riders need to cut off all their toes and their outer three fingers before I will take seriously any of their whining about equipment weight. Without toes, not only would your rotating mass be less, you could wear smaller, more aerodynamic shoes.
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Maybe they add to the "flywheel" effect.
Or Maybe they don't.
Or Maybe they don't.
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You are looking at moment of inertia, not lifting. This is a rotation. It matters, but MOI is what you need to google.
We go real light on shoes - cleats - Ti hardware etc as it matters and there is no UCI limit on it.
We go real light on shoes - cleats - Ti hardware etc as it matters and there is no UCI limit on it.
Last edited by Doge; 02-17-16 at 03:25 PM.
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I think this is incorrect. Cycling shoes do not rotate about an axis. Just because the shoes are helping to pedal circles, doesn't mean they are rotating like the crank or like wheels. Barring an accident, the tops of the shoes are always up, the bottoms always down. No rotation.
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Forget about trying to justify it. Just go buy yourself a new pair of shoes.
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A weight weenie friend of mine did exactly the same type of calculations. He really worked hard shaving grams off of all of his gear. Shoes were one of the biggest weight savings.
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I think this is incorrect. Cycling shoes do not rotate about an axis. Just because the shoes are helping to pedal circles, doesn't mean they are rotating like the crank or like wheels. Barring an accident, the tops of the shoes are always up, the bottoms always down. No rotation.
Cycling stuff is very hard to calculate what is really happening in 3d, but the MOI principle was good enough for me.
I had these once (really) https://sheldonbrown.com/shimano1982/pages/15.html
In that case both circle were more nearly concentric. But it doesn't matter.
Last edited by Doge; 02-17-16 at 06:31 PM.
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200 grams is a serious chunk -- like going from a winter mountain bike shoe to a carbon road shoe ---- Yes- you will feel it and it is worth it
The financial component ? Thats up to what your wallet can stand .
If i had the bucks , custom Bonts and Rocket-7's would be all i would run
The financial component ? Thats up to what your wallet can stand .
If i had the bucks , custom Bonts and Rocket-7's would be all i would run
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Moment of inertia is close to irrelevant. As a ap physics c mechanical student, I calculated this in terms of power saved assuming a 175 mm crank (200mm center of mass) and 90 cadence. The watts saved due to rotational effects are .027, so nearly nothing.
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I guess I should also ask the mass of the shoe and foot you used.
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I'll check it out, but it feels like lifting to me. Rotation adds factors,
but you still have to raise your feet about 14" over and over again.
The 200g in question is in addition to 200g already saved going from
Sidis to S-works, for about $100. As a side benefit, several women have commented favorably on the shoes,
so that may help the MOI in some subtle way.
About another $145 to upgrade to Giro uber-fancy, uber-light.
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I'll check it out, but it feels like lifting to me. Rotation adds factors,
but you still have to raise your feet about 14" over and over again.
The 200g in question is in addition to 200g already saved going from
Sidis to S-works, for about $100. As a side benefit, several women have commented favorably on the shoes,
so that may help the MOI in some subtle way.
About another $145 to upgrade to Giro uber-fancy, uber-light.
but you still have to raise your feet about 14" over and over again.
The 200g in question is in addition to 200g already saved going from
Sidis to S-works, for about $100. As a side benefit, several women have commented favorably on the shoes,
so that may help the MOI in some subtle way.
About another $145 to upgrade to Giro uber-fancy, uber-light.
You are primarily lifting your leg. More than likely, outside of a sprint the pedal is lifting your leg by the other pedal.
Waaay back in the 80s I was a no car Physics / EE student that sold my car to save the world and commuted on bike. I'd bring all this stuff into calculus class and general physics class and my CalTech (edit: I was not at CalTech - he was) professor basically said it was all too hard when you brought in real world stuff - like getting knocked off course by pebbles, stopping pedaling yada yada.
The problems are fun and the physics principles apply, but an educated experienced guess works as well - normally better.
If it moves - cut weight.
The farther it is from the axis - the more it matters.
People adapt to mechanical systems. Froome proves you can't calculate this stuff.
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a=v^2/r (v is found using cadence and circumference), I did not find it for increasing from 90 to 130, only 90, because that is a typical cadence, therefore no time delta was necessary, also the mass of the shoes and foot are irrelecant, we are describing delta power, so only the changing variables are necessary (the power to accelerate a 200g mass at a radius of .2 meters)