Center of gravity 20" vs 26". How much does your engine weigh?

boyntonstu

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The axles of 20" bikes are by definition 3" closer to the ground than 26" bikes.

If you make both seat heights equal, there will be lots of room below your seat on a 20" bike for engine mounting.

I am not positive, but it may be possible to rear mount an engine on a 20" bike and have a low CG.

https://www.bikefriday.com/bicycles/small_wheel_myths

Small Wheel Myths

Many folks who remember riding their 20-inch bike chasing an older brother or sister on a larger wheel bike ask the obvious question:

Don't you have to pedal more?

The simple answer is, No!

It's all in the gearing. A single turn of the pedals on a Bike Friday will cover the same ground as that of a regular wheeled bike — the small wheel just turns a little more.

Other small wheel facts:

The gears on a Bike Friday are configured to match the ratios of a regular bike
Small wheels climb better due to a smaller diameter that needs to be rotated.
Small wheels accelerate faster.
Small wheels are more responsive — they turn and steer more easily.
Small wheels, having a lower surface area, have lower wind resistance in headwinds.
When riding in a group, small wheels enable you to get closer together and draft better.
We've seen tests that shown up to 16 mph, the small wheel is more efficient that a big wheel. Between 16 and 33 mph there is little difference.
Small wheels are lighter [they simply have less
material.]
Small wheels are stronger [less spokes are
needed for the same durability].
 
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The axles of 20" bikes are by definition 3" closer to the ground than 26" bikes.
If you make both seat heights equal, there will be lots of room below your seat on a 20" bike for engine mounting.

Sure, on a girls bike with no top bar, or do you plan to mount the engine on top of the top bar?

I am not positive, but it may be possible to rear mount an engine on a 20" bike and have a low CG.

If you attach the engine to the side of the wheel at the axle maybe but then the weight is not centered, above the wheel of course not a low center of gravity.
 
Most kits it doesn't matter once you get into motion. Even a FD weighing 20lbs on the rear weighted to one side you don't even notice the weight, not an issue in my book.
 
Heres a over 30lb Lifan 97cc/2.5hp Friction Drive.

Getting a working kick-stand becomes more of an issue.

Not my MB.
 

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Sorry, not my build.
It's from the other forum, and it might not be proper to link.
Google "Lifan 97cc/2.5hp Friction Drive"

Tire wear tends to be about 20% worse on friction drives than other drives.
 
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