Mission Control and the "efficiency" of the human body

[Art Deco]

i have strong legs, but a bad heart. between us, @Stefan Mikes and i could probably make one very robust cyclist!

You need to find a nice tandem...

 

[Art Deco]

So, in physics, a watt hour and a kilocalorie are very close to the same amount of energy. 100 wH is 86 kCal.

I believe the SL motor to be around 85% efficient, taking drivetrain into account, so those 100wH might produce 85wH of forward moving energy and another 15 of heat from friction, noise etc. I have no idea how "efficient" the human body is, but since Mission Control saves both rider output in watts and calories burned, we can deduce that Specialized seems to think the human body is only around 25% efficient in converting calories to rotational energy. For me, a ride with 1,000 calories burned, 300wH of rider power and 30 wH of battery used used reports a "support percentage" as expected from the wattage numbers of around 10%... but 300wH in physics is only 258 kCal, not 1,000. I know for sure that there's no way I'm only burning 258 calories on an hour and a half 200 watt average output bike ride, which seems to support the motor being 85% efficient in converting energy to motion and a human on a bike being more like 25%.

Biomechanical physicists in the room, does that seem right? Or is one of the various numbers way off?

/offtopic Since nobody mentioned Steve Jobs' fascination with the efficiency of the bycycle I dug up a old link

How the bicycle beats evolution and why Steve Jobs was so taken with this fact | Bike Boom

/ end offtopic

 

[Stefan Mikes]

/offtopic Since nobody mentioned Steve Jobs' fascination with the efficiency of the bycycle I dug up a old link

How the bicycle beats evolution and why Steve Jobs was so taken with this fact | Bike Boom

/ end offtopic

Steve Jobs was also very wrong in some matters of vital importance, so why mention him? The article you quoted describes findings of two men by name Wilson...

 

[Stefan Mikes]

Going slowly is not the best way to get home on a low battery like one might think.

I don't think you really understood the explanation. Going home slowly on low battery is the best solution. Precisely, reducing assistance to reasonable minimum and increasing human contribution in the bike motion. Slow riding equals to low air drag in the first place, and air drag is the main resistance during riding on the flat.

 

[kahn]

I don't think you really understood the explanation. Going home slowly on low battery is the best solution. Precisely, reducing assistance to reasonable minimum and increasing human contribution in the bike motion. Slow riding equals to low air drag in the first place, and air drag is the main resistance during riding on the flat.

One has to remember that LOW battery in a Specialized e-bike (and maybe others, too) might mean the motor will shut down rather than drain it completely. So one does have to carefully monitor battery level and determine when to slow the riding so that there's still power left to complete the ride. Is low battery 20%, 15% or 10%?

 

[Stefan Mikes]

One has to remember that LOW battery in a Specialized e-bike (and maybe others, too) might mean the motor will shut down rather than drain it completely. So one does have to carefully monitor battery level and determine when to slow the riding so that there's still power left to complete the ride. Is low battery 20%, 15% or 10%?

I understand your drawing a parallel. Direct answer is: The unusable Specialized battery level is 5%. In Giant e-bikes, you should be afraid at 20%: The motor drains the last 20% in very few kilometres there.

 

[kahn]

I understand your drawing a parallel. Direct answer is: The unusable Specialized battery level is 5%. In Giant e-bikes, you should be afraid at 20%: The motor drains the last 20% in very few kilometres there.

Thanks for the answer. Now, what time is it over there? Are you awake at all hours?

 

[Stefan Mikes]

It's 05:16 a.m. I get up early, and am taking naps in early evening