Wheel build

[halfmedley]

If I were to take the motor from my Mistral (26in wheel) and have it built into a 700c wheel (on a different bike), what would that do to the performance of the motor? According to electricbikesales website, the Mistral motor is 200W nominal, 720W peak.

Am I right in thinking it'll have the same effect as noted by Flecc's Quando/Torq comparisons, i.e. smaller wheel = better hill climbing, larger wheel = better speed on the flat, or am I being too simplistic?

 

[john]

Yes, hill climbing will be reduced by about 10% (in theory at least).

Top speed will increase by about 10%, but whether you achieve that speed will depend on whether the motor can produce enough power to overcome the resistance at the time (depending on tyres, slope, wind etc).

 

[flecc]

From experience, doing this can result in more disappointing hill climbing than expected. When dealing with very limited amounts of power, a critical point can be reached when the results fall short of what should happen, as John implied when saying "in theory at least".
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[Trumpet]

From experience, doing this can result in more disappointing hill climbing than expected. When dealing with very limited amounts of power, a critical point can be reached when the results fall short of what should happen, as John implied when saying "in theory at least".
.

Yes, speed falls - you drop down the efficiency curve quite quickly, not as quick as the tail-off at the top end but it is significant. You lose much more than just the straight linear ratio between wheel diameters and it can be a cascading reduction as you are left with rapidly reducing (EDIT) efficiency and up grinding to a near-halt. There is enough torgue to pull you along at a few mph but it is a bit like being stuck down a power well and not being able to get out.

Simulator and useful links...
ebikes.ca Hub Motor Simulator

 

[halfmedley]

Thanks for the advice, seems like the theory and the reality wouldn't necessarily be the same. I am considering upgrading to a more expensive machine and was considering scavenging the motor etc from the Mistral for another project, but now perhaps I might just sell the complete Mistral instead.