Help with a challenge

[BossBob]

Which goes like this ........

By a second hand pedelec with a 20" wheel and 24v motor (assumed to be 200w hub)
fit the motor into a 26" wheel - existing wheel re-spoked to suit
Get a 36v controller - as previously discussed on here, from Ebay @ £20
A 36v battery, and move the throttle from the donor pedelec to drive it.

So ..... for those that know how to work out the effect of "over volting" the 24v motor, and the extra distance gained per rev by fitting it in a 26" wheel,

What are the likely final figures?

Would it gain in power? i.e. from 24v to 36v is a 50% gain, so is it now a 300w motor?
would it have a higher top speed? and would it have the power to reach the theoretical speed?

If only I knew how to work it all out ..... hmmmm

any rough figures as a guide would be appreciated,
Thank you for your time and effort (and knowledge)

Rab

 

[keithhazel]

mmmmmmmmmm fife scotland....ive bought 3 folding electric bikes from that neck of the woods in the last 8 months....popular there or what

having just looked back at records the last 2 was from someone called ....you guessed...Bob...
is this a small world...lol...im guessing its you, hope things are going well with your project.
regards keith

 

[BossBob]

mmmmmmmmmm fife scotland....ive bought 3 folding electric bikes from that neck of the woods in the last 8 months....popular there or what

Hmmm .... now why would you buy 3?

having just looked back at records the last 2 was from someone called ....you guessed...Bob...
is this a small world...lol...im guessing its you, hope things are going well with your project.
regards keith

LOL

No mate, not me ...... I've never had one folder never mind two

And my project aint off the ground yet ..... it is just a cunning Scotsmans Muse

Rab

 

[flecc]

Yes, in broad terms the arithmetic holds good. The motor would become 300 watts and therefore be 50% more powerful. If it's speed before was 15 mph, upping from the 20" to the 26" wheel would make that 19.5 mph, though wind resistance at the higher speed might knock off the half mph. Also, 300 watts isn't much at that speed to oppose headwinds and slopes, so adverse conditions would have a marked affect of performance.

This arithmetic progression isn't infinite though, you couldn't put the motor in a 40" wheel and have the bike do 30 mph, since that 300 watts would be insufficient, this being another form of adverse condition.
.

 

[fishingpaul]

a lot of 20 inch wheel bikes use the same motors as 26 inch wheels,and only do around 12.5mph,the powabyke folder is one such bike, and top speed is not specified in their specifications.putting a 20" motor into a 26"wheel may only restore 15mph.

 

[Jeremy]

If you know the motor type, and it's one of the ones listed in the simulator, then try here: ebikes.ca Hub Motor Simulator and enter any permutation you wish.

The results are fairly accurate, but obviously only give theoretical top speed unless you allow for the known power required at any given speed/wind/gradient/bike type. You can find out the latter information from this power calculator here Bicycle Speed And Power Calculator, which also gives reasonable results.

For an example, using the eZee motor:

24V 8Ah battery, 20A controller, 20" wheel gives max power of about 290W at 7.5 mph. The zero power speed is about 12mph.

36V, 8Ah battery, 20A controller, 26" wheel gives max power of about 490W at around 17mph. The zero power speed is about 22mph.

If your bike is an upright style, with reasonably low rolling resistance tyres, then in no wind or gradient it will need about 200W to do about 17mph.

Jeremy