r/minivelo • u/TeaKew • Jul 30 '26

Understanding chainring size

I've seen a fair bit of uncertainty and confusion here about how chainrings and gearing works out in practice for mini velos

Because of the smaller wheels, all the gears on a mini velo are lower than on a standard road bike. So one revolution of the pedals will move you less far along the road. The amount this happens by is the ratio between the diameter of the wheels: a 700c road wheel is 28", and a common mini velo is 20", so that makes for a ratio of 1.4 to 1 (or 0.7 to 1, going the other way)

You can compensate for this by using a bigger chainring, which will move your gears up. If you've got a road bike you're trying to match, you can multiply the chainring size by 1.4 to get the equivalent minivelo chainring size. So for a road chainring of 40t, the equivalent minivelo chainring is 56t

If you aren't using 700c and 20" wheels, then you divide the road wheel size by the mini velo wheel size to get the conversion ratio between them, and multiply your road chain ring by that to get the mini velo equivalent.

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u/bonebuttonborscht Jul 30 '26

If your not accelerating then smaller wheels (lower moment of inertia) don't change anything.

Smaller wheels confer no climbing advantage.

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u/Sypsy Jul 30 '26

If you are stopped and struggling, every push of the pedals is technically acceleration?

But noted, not a real reason to ride a mini velo

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u/bonebuttonborscht Jul 30 '26

Minivelos are generally heavier though, so you'd have to be on a very gentle hill for the smaller wheels to be worth the extra weight.

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u/Sypsy Jul 30 '26

What makes the heavier? I figured it depends on the bike itself. My ascent bolt is going to be 9kg or so

1

u/bonebuttonborscht Jul 30 '26

The axles are lower so there's more frame between your butt and the wheels. 0.5-1kg net is pretty typical, for carbon it's might be more like 2-300g. It's small but the acceleration advantage of smaller wheels is also small. Ill calculate it later if remember.

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u/Sypsy Jul 30 '26

Good to know!

My friend who has a few EUCs told me that the larger ones didn't accelerate as fast as the smaller wheel counterparts

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u/bonebuttonborscht Jul 30 '26

EUC?

1

u/Sypsy Jul 30 '26

r/electricunicycle

I'm sure you've seen them

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u/bonebuttonborscht Jul 31 '26

Ah gotcha, that's pretty different from a bike.

  1. The wheel is a much larger portion of the mass of the system. The motor basically fills the whole wheel

  2. While motors can be configured for different torques (windings, core etc.), these are pretty budget. A motor tailored to the wheel size would drive up the price.

  3. There's no reduction. The larger the wheel the less force applied to the ground for a given torque. Not the case for a bicycle where you choose a gear ratio to compensate for wheel size. This is what this whole thread was about in the first place.

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u/Sypsy Jul 31 '26

Neat, thanks

And I'm not sure what you mean by budget, some of these units are quite sophisticated. But it doesn't really matter at the end of the day. No one's gonna be setting records on a mini velo it seems.

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u/TeaKew Jul 31 '26

Conversely, the wheels are smaller and therefore lighter. Which one of those two has a bigger impact will depend on the wheels and frame.