For those who insist on fat tires (i.e. 3.8" or wider) with hub motor what pedal drive train would you use?

[ebike4healthandfitness]

Multi speed freewheel or cassette with wide q factor?

Single speed freewheel or cassette with regular mtn bike q factor?

Less efficient biomechanics, but choice of multiple gears to increase efficiency vs. More efficient biomechanics but no ability to change the pedal ratio?

Assume a torque sensor is present on both drive train combinations.

 

[offGridDownUnder]

Well, what does the bike have now?

At least that might fit.

 

[ebike4healthandfitness]

Well, what does the bike have now?

At least that might fit.

The frame choice is open ended.

For example, a bicycle like the one below could be used for narrow q factor, 4" tire and single speed use:

Retrotec Fat Single Speed | Whisky Parts Co

whiskyparts.co

 

[offGridDownUnder]

My point is that the existing design makes choices for you.

That chain must clear the tire in any chainline it may assume. The range of chainlines that result from a cassette or freewheel dictate a distance the front sprocket must exceed to prevent the chain from rubbing on the tire. A single speed, or an internal gear hub (IGH) will usually permit choosing the chainline that is closest to the centerline of the bicycle - and it won't be closer than half the width of the tire.

A pinion gear set at the crank would be another way to accomplish this, but frames must generally be designed for this, or you may build a custom frame.

 

[ebike4healthandfitness]

A Shimano 8 to 11 speed cassette is 41.5mm wide. So that means with the chainline on the middle gear of the cassette there must an additional 20.75mm inward distance available so the chain has enough room to move to the largest cog on the rear.

Removing that need for the additional 20.75mm inward distance with a single speed means the tire (and chain stays) can be 41.5mm wider all things equal (re: you add 20.75 mm extra width to both sides of the tire not just the side closest to the chain)

So given two bikes with same q factor and same chainline a single speed allows for a tire 1.63" wider (re: 2 x 20.75mm = 41.5mm = 1.63"). Since most 8 speed to 11 speed mtn bikes can handle a 2.5" tire you can now see how a tire 4.13" wide is possible.