Rider weight and electric bike performance

vfr400

Esteemed Pedelecer
Jun 12, 2011
9,012
3,575
Basildon
Jeez, from an engineering point of view, that's terrible. The general conclusion is correct, but they've missed the point completely. All they did was measure the rolling resistance on a relatively inefficient tyre powered by a relatively inefficient motor system. They could have saved a lot of time and effort and they could have got much more sensible results from here;

Rolling resistance is pretyy insignificant when compared with other energy losses. Air resistance is significantly higher. Look at the charts here:

What they failed to understand is how weight affects hill-climbing. It's very simple. The power to pedal a bike up any incline at any particular speed is directly proportional to the total mass of the bike and rider, so a 100kg rider riding a 25kg bike up any incline will require 25% more power to go the same speed as a 75kg rider on the same bike, or double the power of a 52.5kg rider on a 10kg bike.

On the flat, the lighter rider gets avery small addvantage due to rolling resistance and a lot more advantage due to lower air resistance (smaller size).

On a downhill, the heavier rider gets the advantage, due to gravity pulling him/her down the hill in proportion to the total mass., so it pulls a heavier rider harder.

On any incline, whether up or down, rolling resistance reduces increasingly as the incline steepens, due to the riders weight being resolved into two components - one in the direction of the incline, and the other one, which is the component affecting rolling resistance, at right angles to the incline. To make that clearer, consider the extreme case where the incline would be 90 deg (vertical): Obviously, there would be no rolling resistance.
 

Ocsid

Esteemed Pedelecer
Aug 2, 2017
298
197
78
Hampshire
Jeez, from an engineering point of view, that's terrible. The general conclusion is correct, but they've missed the point completely. All they did was measure the rolling resistance on a relatively inefficient tyre powered by a relatively inefficient motor system.
Missed the science of it to, leaving out pumping potential energy into a "mass", by lifting it higher, ie going uphill.
 

Bonzo Banana

Pedelecer
Sep 29, 2019
123
69
Also the heavier rider may have a lot more muscle mass and be capable of generating more watts so there is a variable there. The chap in that video is quite elderly and dare I suggest not capable of particular high wattage. Soo many variables I would find it hard to make a decent analysis but this video is far too basic. 250W motor assisting a rider capable of generating 300W and having a weight of 100kg compared to a 250W motor assisting a rider of 180W weighing 75kg etc.

It's a bit like the direct drive hub motor they used for that test. Depending on your parameters you can claim that is the most efficient or least efficient motor. Technically it is the most efficient in that it has the smallest amount of energy loss because there are no gears or pulleys its just a brushless motor but then how it applies its power is not optimal for the cyclist and how a cyclist functions.

As ever you can make any conclusions you want really based on how you approach the analysis.

A real world test is much more meaningful.
 

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