Mission Control and the "efficiency" of the human body

[mschwett]

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?

 

[Stefan Mikes]

mschwett: You have figured that out correctly! The efficiency of human body is believed to be 25%.

 

[Art Deco]

Watching and waiting for a 'Steve Jobs' reference ...

 

[BioWheel]

This gets me thinking. What's the most efficient combination of motor output and gearing for the SL? Is it just lowest possible motor setting and smallest gear?

 

[kahn]

This gets me thinking. What's the most efficient combination of motor output and gearing for the SL? Is it just lowest possible motor setting and smallest gear?

Are you on the FLATS, climbing a HILL or climbing a MOUNTAIN?

 

[mschwett]

This gets me thinking. What's the most efficient combination of motor output and gearing for the SL? Is it just lowest possible motor setting and smallest gear?

how are you defining "efficient?" if you mean forward motion produced per battery power used, i'd doubt that it's the lowest setting. most electric motors are most efficient somewhere near their max rated load, maybe 60-80%. we have heard that the SL motor is most efficient at a cadence between 70 and 110. to match up those stats - let's say it's most efficient at 300w * .7 = 210w, you'll need to put in at least 105w, and you'll be going PRETTY FAST on level ground, and likely in a higher gear to match up that much torque and cadence... for an average rider on level ground that works out to about 22mph at 90rpm and 50t in the front with 16t in the back, in terms of peak motor "efficiency." however, you'll get wayyyyyyyyyyy better mileage going slower, since wind resistance is going to be an order of magnitude greater than any inefficiency of an electric motor.

in terms of battery lasting the longest period, that's just you pedaling more and turning the support down lol!

 

[Art Deco]

Are you on the FLATS, climbing a HILL or climbing a MOUNTAIN?

Fighting headwinds? Hauling how much weight?

 

[kahn]

Fighting headwinds? Hauling how much weight?

Sheesh, do you think that there may be too many variables?

I just pedal and hope that the battery/batteries last for the ride - a distance much less than Specialized optimistically conveys in its ad copy!

 

[Art Deco]

Sheesh, do you think that there may be too many variables?

I just pedal and hope that the battery/batteries last for the ride - a distance much less than Specialized optimistically conveys in its ad copy!

That was the point. Set the bike up with a couple of profiles that matter to you by using the slider in MC from 10 percent to 100 percent boost. " Trails, Traffic, Trouble " is how I think.

 

[Stefan Mikes]

I know one thing: Vado SL with Range Extender will take me for at least a metric century in our flatland whatever happens. I like the 35/70 setting that lets me work out, doesn't require changing the assistance level with small inclines and is very easy on the battery.

 

[Art Deco]

@Chargeride said

Eco
Trail
Turbo
Grizzly

Our Rides in Words, Photos & Videos

Cloudy, comfy day for riding on Whidbey Island! Enjoying the cooler (normal) temperatures for the next 10 days, at least. On shore marine flow means the sun doesn't appear until afternoon sometime...maybe 😉. Map My Ride says 11.46 miles; Giant Ride Control have me 11.9... Looking north up...

electricbikereview.com

 

[kahn]

I know one thing: Vado SL with Range Extender will take me for at least a metric century in our flatland whatever happens. I like the 35/70 setting that lets me work out, doesn't require changing the assistance level with small inclines and is very easy on the battery.

As I probably wrote elsewhere, I did a 53 miler with 2,800 feet of gain, some of it quite steep on my aluminum Creo. That ride left me with about 5-6% on the main and Range extender batteries. (maybe I should have gone carbon fiber!)

So I could probably eke out a metric century with less climbing. Although, in this neck of the woods, flatter terrain can be hard to find. If it would not bore me to tears, there is a mup I can get to with a few dips and rises from my home that would be 50 almost flat miles. I could extend it somewhat or repeat a bit to see if I can stretch it to 63 miles or so.

 

[kahn]

@Chargeride said

Eco
Trail
Turbo
Grizzly

Our Rides in Words, Photos & Videos

Cloudy, comfy day for riding on Whidbey Island! Enjoying the cooler (normal) temperatures for the next 10 days, at least. On shore marine flow means the sun doesn't appear until afternoon sometime...maybe 😉. Map My Ride says 11.46 miles; Giant Ride Control have me 11.9... Looking north up...

electricbikereview.com

Instead of Grizzly, I have occasionally longed for what I call a "kick-ash" button. Just another quick hit of juice.

 

[Stefan Mikes]

"There was a Russian guy who got into a Western made car. The car had a manual gearbox. The man was quite properly upshifting; the car was gaining speed.
Already in the sixth gear (the car was moving very fast), our man -- with a triumphant grin -- decided to use the very last gear:
-- Now... R like Rocket!"

 

[ActionJackson]

As I probably wrote elsewhere, I did a 53 miler with 2,800 feet of gain, some of it quite steep on my aluminum Creo. That ride left me with about 5-6% on the main and Range extender batteries. (maybe I should have gone carbon fiber!)

The real question is - could you have even done that without the benefit of the motor assist?

 

[kahn]

The real question is - could you have even done that without the benefit of the motor assist?

At this point, there is no real question. I could NOT have done it without motor assist.

At the time I had a custom titanium bike built, they did not offer TRIPLES. I managed but it got harder and harder. I then brought it to a shop where they upgraded the freewheel with a DINNER plate top gear. It was also fine for a while. I had that bike converted to a front motor hub e-bike. I guess the old joints (one hip replaced twice) and expanding girth just caught up. In March I went for the aluminum Creo because I wanted the lighter weight e-bike that performed a bit more naturally and the battery on my converted unit was losing power, therefore, range. The front mount motor made the bike twitchy or squirrelly on steeper hills, although I believe it is/was more powerful than the motor in the Creo.

I would like to think that I can return to some non-e-bike riding and maybe I can if I limit the trips I do to easier rides with fewer climbs. Else, anybody want a Trek Madone, about 52cm!?

 

[Stefan Mikes]

I need to mention my bad legs force me to use a lot of assistance (the average assistance of today was 45%), and that makes my range on Vado SL rather short. And kahn rides a road e-bike (less air drag). Still, Vado SL range is impressive!

 

[mschwett]

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

 

[Stefan Mikes]

As I say, mschwett, Range Extenders are not that expensive. One costs less than a Garmin 830 (which I eventually won't buy) We can use more assistance!

 

[BioWheel]

how are you defining "efficient?" if you mean forward motion produced per battery power used, i'd doubt that it's the lowest setting. most electric motors are most efficient somewhere near their max rated load, maybe 60-80%. we have heard that the SL motor is most efficient at a cadence between 70 and 110. to match up those stats - let's say it's most efficient at 300w * .7 = 210w, you'll need to put in at least 105w, and you'll be going PRETTY FAST on level ground, and likely in a higher gear to match up that much torque and cadence... for an average rider on level ground that works out to about 22mph at 90rpm and 50t in the front with 16t in the back, in terms of peak motor "efficiency." however, you'll get wayyyyyyyyyyy better mileage going slower, since wind resistance is going to be an order of magnitude greater than any inefficiency of an electric motor.

in terms of battery lasting the longest period, that's just you pedaling more and turning the support down lol!

Exactly. You understood my question and thank you for the clear explanation. Going slowly is not the best way to get home on a low battery like one might think. Thanks.