There are lots of variables here, and some of them are not easily quantifiable.

In terms of "gear ratio" the important thing is how far the unicycle moves for every inch your feet move.

This can be expressed as a ratio of the crank length to the radius of the wheel. As we're dealing with lengths (rather than areas) it works just as well to compare the crank length with the diameter of the wheel, or even (should you choose) the circumference.

We're used to thinking of cranks in millimetres, and wheels in inches.

For those of you who have forgotten, there are 25.4 millimetres in an inch.

As near as makes no odds, a 150 mm crank is 6 inches long.

Put 6 inch cranks on a 24 inch wheel, and the ratio of crank length: wheel diameter will be 1:4.

Now, put some 125 mm (5 inch) cranks on a 20 inch wheel.

Again, the ratio of crank length:wheel diameter will be 1:4.

In each case, if your foot moves an inch, the uni moves 4 inches.

And, in the short term, riding a 20 on 125 mm cranks, or a 24 on 150mm cranks will feel pretty similar.

But the big wheel will roll over bumps more easily. It will ahve more "flywheel effect" so it will be more stable.

On the other hand, the small wheel will be lighter and more manoeuvreable.

And the 1:4 ratio won't work the same outside a certain range. As a thought experiment, consider riding a 1 inch wheel on 1/4 inch cranks. It won't go as fast or as easily as the 20 on 125s!

Now as a thought experiment, try riding a 48" wheel on 12" cranks. Not easy.

On extremely short cranks, you are only using a tiny bit of the available muscle movement in your legs. On extremely long cranks, you won't be able to move your legs smoothly in the huge circle.

But within common sense limits:

Big wheels go faster, but ar eharder to get up or down hill.

Short cranks go faster, but are harder to get up and down hill.

In terms of "gear ratio" the important thing is how far the unicycle moves for every inch your feet move.

This can be expressed as a ratio of the crank length to the radius of the wheel. As we're dealing with lengths (rather than areas) it works just as well to compare the crank length with the diameter of the wheel, or even (should you choose) the circumference.

We're used to thinking of cranks in millimetres, and wheels in inches.

For those of you who have forgotten, there are 25.4 millimetres in an inch.

As near as makes no odds, a 150 mm crank is 6 inches long.

Put 6 inch cranks on a 24 inch wheel, and the ratio of crank length: wheel diameter will be 1:4.

Now, put some 125 mm (5 inch) cranks on a 20 inch wheel.

Again, the ratio of crank length:wheel diameter will be 1:4.

In each case, if your foot moves an inch, the uni moves 4 inches.

And, in the short term, riding a 20 on 125 mm cranks, or a 24 on 150mm cranks will feel pretty similar.

But the big wheel will roll over bumps more easily. It will ahve more "flywheel effect" so it will be more stable.

On the other hand, the small wheel will be lighter and more manoeuvreable.

And the 1:4 ratio won't work the same outside a certain range. As a thought experiment, consider riding a 1 inch wheel on 1/4 inch cranks. It won't go as fast or as easily as the 20 on 125s!

Now as a thought experiment, try riding a 48" wheel on 12" cranks. Not easy.

On extremely short cranks, you are only using a tiny bit of the available muscle movement in your legs. On extremely long cranks, you won't be able to move your legs smoothly in the huge circle.

But within common sense limits:

Big wheels go faster, but ar eharder to get up or down hill.

Short cranks go faster, but are harder to get up and down hill.

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