Speed, Distance, and Energy Consumption

bikerjohn

Well-Known Member
How far and fast one can go on an e-bike depends on several factors...

On any bike e-powered or non e-powered, averaging 25 mph for a long distance (say 50 miles) would require a high amount of rider input as well as a high gear inch ratio. Combining those two aspects with utilizing a riders average sustained cadence capability, enables a cyclist to reach a maxim sustainable average speed. On a non-power assisted bike, the cyclist would need to be an athlete of above average ability. Perhaps that same above average athlete could get it done on the right e-bike and hardly break a sweat. But to be realistic about commuting expectations using an e-bike, a 25 mph average speed is pretty much beyond the capability for the typical commuter cyclist

Consider long distance assistance can be supplied with an electric motor.
An extreme example of the benefit from power assisted biking can be illustrated by answering a question from a would be e-bike commuter:
A cyclist interested in commuting a round trip distance of 42 miles, would prefer to accomplish that commute in under an hour each way.Expecting a need to average 25 mph on the commute. Is it possible to accomplish that on an electric bike?
Answer: Perhaps that is a bit of a stretch of capability. Keep in mind that traveling a distance of say 40-50 miles at an average speed of say 25 mph, would require a large amp hour capacity battery (perhaps upwards of 36+ volts and 20+ ah) for a hub motored e-bike going that distance and speed. Also bear in mind that weight, wind, and rider effort are contingent. At a slower pace, using more rider effort, 40-50 miles can be achieved with 36 volts and 12 ah capacity. The most significant difference required to accomplish that distance is greater rider input (substantial) and a lower average speed (say 15 mph).

The greater the speed and distance on a bike, the greater the energy requirement. The greater the assistance provided by the motor of an e-bike, the greater drain there will be on battery energy.

Understand too, that the greater your pedal effort, the less power drain there is on the battery of an e-bike. For example, if the goal for average speed is 25 mph, and if "full throttle" assist is needed in order to accomplish that speed average, then battery power consumed will be greater than if you were able to achieve that speed average with a low power assist setting.

The greatest asset to conserving battery power is pedaling effort! Adding more of your own pedaling effort, will decrease battery power consumption. Perhaps regenerative braking can help extend battery power too. But I suspect the regenerative gain is of minimal benefit for extending battery power availability on long commutes. Riding an e-bike at a substantial speed, mile after mile, without pedal effort is an unreasonable expectation.

My experience commuting on an e-bike is with the Zurich 350 IX, I have found that my speed is limited by the gearing of the Nexus hub along with my ability to maintain a high cadence pedal effort, -regardless of electric assistance. If I could maintain a cadence of 100 rpm in high gear on the Zurich, then my maximum average speed would be about 23.5 mph. Therein lies the limitation of speed on any bike you intend to pedal. My best steady cadence is about 85 rpm. I can reach a cadence upwards of 100 rpm but only for fractions of a minute. So it is a combination of a cyclist's cadence capability, and gearing which combined will determine maximum speed. The assistance of an electric motor enhances ones ability in accelerating and maintaining a maximum speed, which again is limited by bike gearing and average cadence.

To sum it up:
A maximum sustainable speed with the Zurich or with any bike is contingent on rider weight and input effort, as well as environmental factors such as wind. Other factors with an e-bike to consider are motor wattage, voltage and the energy capacity (amp hours) of the battery.

commuting with the Zurich 350 IX:
->My best speed average on my 16-18 mile r/t commute has been about 19.5 mph;
->Inbound, the 8 miles from my house to Hilton is slightly downhill, and my maximum sustainable average speed is about 20.5 mph.
->If I could maintain a cadence of 100 rpm in high gear, with the configuration of the Zurich bike, my speed average would be 23.5 mph; (I have not been able to maintain that cadence for longer than a fraction of a minute at a time.)
->I often reach a peak speeds of over 30 mph, but that is on a downhill, and has little to do with e-motor assistance.
->At full throttle, I can discern power assistance up to 24 mph or so.

Primarily because of the gearing configuration with the 7 speed Nexus hub, a lighter rider weight would not achieve much faster average speed. But a lighter weight would enable less battery power drain over a given distance.
 
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MarcD

Active Member
You can actually come up with some decent estimates for this, using some online tools and a calculator. Start with this speed and power calculator. I am attaching a screen grab using my stats in a 22mph on flats on my Turbo as an example.
  1. We see that you need 401 watts to maintain that that speed with my weight, tires, etc...
  2. Assume the Turbo battery is 90% usable energy at 504 watt hours = 453.6 watt hours of available energy
  3. I know that I can generate 115 to 135 watts on my road bike. I pedal easier on the e-bike, so let's assume I am putting in 90 watts
  4. This nets 311 watts required from the motor
  5. 453 watt hours / 311 watts = 1.46 hours of energy
  6. 1.46 hours * 22 miles / hour = 32.12 miles.
Note that this is an overestimation for one big reason: It does not factor in the energy to GET to 22mph, only sustain it. The more stops, slow downs, turns, etc, the more energy you consume in acceleration

I know my real world range is closer to 26 miles on the bike with about 30 stops and one big hill, so there is about a 22.5% efficiency penalty in urban riding in my case.

Watt_Estimate_Turbo_Flat_22mph.png

Of course these are estimates, but can help figure out where you stand. You can also reverse the process - if you know pedal assist level X limits motor output to Y watts, then you can figure out what your watt input must be to maintain a certain speed.