Gear selection/battery life/physical energy

[2WheelsNot4]

I think I know the answer to this and its possibly a reflection on myself for not using the gears to their fullest extent. But does gear selection drain or improve battery life ?. With the trade off concerning how much spinning ofo the cranks is needed(Cadence) to maintain speed. I always feel that if you're spinning too much its aa drain on your physical energy levels.

 

[Mikerb]

Most motors are at their most efficient if cadence is at least 70 rpm........meaning they produce more torque per watt . So spinning rather than grinding is the most efficient use of battery and also kindest to drivetrain components. Rider energy use is aerobic rather than leg power.

 

[B1rdie]

If the energy needed to take you plus your bike to a certain altitude is a given, then, the more you put physical, the less battery energy is consumed to get there, for sure. The problem then is how tired and wasted you will be on the way down and how this will lessen the joy and increase the danger of the DH ride.

 

[Mikerb]

If the energy needed to take you plus your bike to a certain altitude is a given, then, the more you put physical, the less battery energy is consumed to get there, for sure. The problem then is how tired and wasted you will be on the way down and how this will lessen the joy and increase the danger of the DH ride.

That sounds logical but time is also a factor. So if by using a lower power mode it takes longer to achieve the climb you may use just as much battery as using more motor power for less time. Another factor is momentum. If by using a higher power mode you are better able to maintain momentum you save battery. Personally I use gearing and power mode combination that results in the optimum speed, flow and minimum leg effort so use emtb mode almost exclusively with short bursts of turbo when needed to maintain that flow. I want full power in my legs for the downhill!!.......and with a chain still in one piece.

 

[SwampNut]

The motor part of the equation is interesting. Car electric motors don't have variable gearing (outside of a couple of oddballs) because it's generally viewed as not mattering. Would it matter on an e-bike? It certainly matters for your human energy which is more like a gas engine; having a limited effective range. So YOUR effect on battery life is certainly based on how much power you put down.

Keep in mind that horsepower is a function of torque times RPM. And horsepower is a measure of work actually done. Horsepower can be correlated to watts (about 746 watts to 1 HP). I think the motor would be producing the same amount of work, within a small percentage, as the watts it takes in. Your human power would vary based on cadence.

 

[rzr]

physical energy - every one is different, but cadence 85-95 is considered as most efficient, but it also depends if you have clipless pedals or flats.
When I ride my ebike, I realised that when i climb with higher cadence (>75-80) it's easily to be lazy and motor produces more power (comparing to mine)
If I want to train a bit harder, I prefer to stay with lower cadence (65-70rpm and >300W for few minutes) on steep climbs, like on my analog bike - I ride flats.

On a road bike I keep cadence 90-100 when i want to produce more power, but with clipless pedals.

 

[SwampNut]

When I ride my ebike, I realised that when i climb with higher cadence (>75-80) it's easily to be lazy and motor produces more power (comparing to mine)

This is important, and it varies by motor and the programming. I've read a lot of claims that my Shimano likes to run at higher cadence and will make more power. My seat of the pants experience agrees. There's also the programming of power curves that you can do on most motors.

 

[CarbonMan]

As people above have noted, motors like higher rpm to put out more power for any given torque setting.

Motors will put out full power only at the proper rpm or higher.
Example: Perf Line CX is 750W max, 85 Nm max.
Power is a function of torque and rpm: W=Nm/sec = Nm * rad/sec.
750W/85Nm=8.82 rad/sec= (8.82 rad/s) / (6.28 rad/rev) = 1.40 rev/sec = 84.2 rpm
So in max power mode, this motor can't get to full power below ~85 rpm. As rpm drops off from there, so does power even if it's still putting out full torque. Above 85 rpm or so, the controller probably limits torque to hold 750W max (at least in USA, that's the max allowable for Class 1, Class 2 and Class 3 ebikes).

At lower power modes, the above holds true except that pedaling faster than 85 rpm should keep putting out more power until you somehow manage to pedal so fast that you hit the 750W limit. In Tour mode (~30 Nm max) that'd be almost 240 rpm...

This doesn't account for motor efficiency, heat buildup vs rpm, how the controller works, etc etc; but the general rule is pedaling faster gets more power from the motor for any torque setting, until you hit the limit.

Pedaling faster, up to a point, is more efficient for your legs to make power too.