Hill climbing ability and wheel size

[AndyOfTheSouth]

Is there a simple relationship between wheel size and hill climbing ability for any given motor torque?

For example, if a comparison were to be made between a Forza and a Torq, is there a simple percentage difference in their hill climbing capacity? Or what if the same motor were put in a 20” wheel, I know that it would climb better, but by how much and how would it be expressed?

I think this is a useful topic because it has implications for choice of bike to convert and between products generally if they share the same motor.

 

[daniel.weck]

I will soon be lacing a motor designed for a 26" front wheel...on a 16" Brompton rim (406mm)...a bit extreme, but it should prove a point
I put my money on: tons of reliable pulling torque, but very poor cruising speed.

 

[AndyOfTheSouth]

Hi Daniel.

Thanks for this rapid response. I am sure you are right, but it must be possible to say in advance what the benefit (and drawback) would be.

The comparison between the 26" Forza and larger wheeled Torq must be easily expressed, for example.

Andy

PS it will still be very interesting to hear for your experience, though.

 

[flecc]

There's two elements to this. The first is the direct ratio of the two relative wheel sizes which is easily worked out. The other element is the mechanical advantage a smaller wheel has, the smaller the size, the greater the advantage.

The original eZee Torq and the Quando used the identical motor/controller/battery setup, the Torq with a 28" wheel, the Quando with a 20". The Torq with this 11 stone rider could only manage a 6% slope unaided by pedalling, failing after a while on 7%. From that you might calculate that the Quando should manage 8 to 10% unaided. In fact it could handle 12% with a rolling start, and even take off from a standstill on 12% without pedal assistance. That gives an idea of the scale of the mechanical advantage of the smaller wheel, approximately 40% gain in addition to the wheel size gain changing from a 28" wheel to 20" wheel.
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