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Weight Weenie calculation

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Weight Weenie calculation

Old 02-17-16, 02:16 PM
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woodcraft
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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.
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Old 02-17-16, 02:19 PM
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Love it.
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Old 02-17-16, 02:30 PM
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I don't worry about any weight except what is attached full time to the bike. There are too many other things to worry about re: shoes to even consider the weight...within limits of course.
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Old 02-17-16, 02:39 PM
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No. The weight saved on the shoe at the bottom of the pedal stroke is offset by the weight saved on the shoe at the top of the pedal stroke.
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Old 02-17-16, 02:42 PM
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Originally Posted by Danny01 View Post
No. The weight saved on the shoe at the bottom of the pedal stroke is offset by the weight saved on the shoe at the top of the pedal stroke.
Exactly, its just weight, don't account for the lifting
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Old 02-17-16, 02:49 PM
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Also, you forgot to take into account the aero drag (from all 360 degrees since the shoes are rotating) of the new shoe vs the old shoe.
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Old 02-17-16, 02:54 PM
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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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Old 02-17-16, 02:54 PM
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Originally Posted by woodcraft View Post
- Ignoring smaller factors, Effort is saved from lifting less weight from bottom of pedal stroke to top of pedal stroke
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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Old 02-17-16, 02:55 PM
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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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Old 02-17-16, 02:58 PM
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Maybe they add to the "flywheel" effect.

Or Maybe they don't.
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Old 02-17-16, 03:05 PM
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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.

Last edited by Doge; 02-17-16 at 03:25 PM.
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Old 02-17-16, 03:06 PM
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Originally Posted by Seattle Forrest View Post
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?
I thought about this after I posted it. It's a dumb question. Obviously asked by a moron.
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Old 02-17-16, 05:50 PM
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Originally Posted by Doge View Post
You are looking at moment of inertia, not lifting. This is a rotation. It matters, but MOI is what you need to google.
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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Old 02-17-16, 06:05 PM
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Forget about trying to justify it. Just go buy yourself a new pair of shoes.
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Old 02-17-16, 06:14 PM
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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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Old 02-17-16, 06:27 PM
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Originally Posted by Igualmente View Post
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.
The axis is not the same as the cranks but if the ankle does not move (it does) it is still a circle. Just the axis is offset by sole/platform height.
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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Old 02-17-16, 06:50 PM
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The answer is obvious: Ride shoeless, attach plates to your feet with velco or Loctite. Save weight, save money and win races.
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Old 02-17-16, 07:34 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
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Old 02-17-16, 07:41 PM
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What goes around, comes around.
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Old 02-17-16, 07:52 PM
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Originally Posted by Doge View Post
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.
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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Old 02-17-16, 07:54 PM
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As a comparison, saving 300grams on tires will save about 2 watts total (weight + rotaional effects)
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Old 02-17-16, 07:56 PM
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Originally Posted by kpotier16 View Post
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.
What rate of acceleration did you use? So as the cyclist increased from 90 to 130 - what was your time delta?
I guess I should also ask the mass of the shoe and foot you used.
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Old 02-17-16, 08:12 PM
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Originally Posted by Doge View Post
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.


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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Old 02-17-16, 08:31 PM
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Originally Posted by woodcraft View Post
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.
You got it right. It is rather complicated. The mechanical system is not so much, but the human part is. And the mechanical becomes more complicated when you add change in speed - which is real.
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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Old 02-17-16, 09:23 PM
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Originally Posted by Doge View Post
What rate of acceleration did you use? So as the cyclist increased from 90 to 130 - what was your time delta?
I guess I should also ask the mass of the shoe and foot you used.
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)
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