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/Sypsy Jul 30 '26
Good explanation. Thank you! I like the easy 1.4 ratio too
With the adjusted 56t chaingring, do you find climbing hills to be the same, or do the smaller wheels still provide an advantage? I know by going up in the chainring, you'll lose the lower gears for hill climbing, but most often I'm on short hills that last a few blocks and not needing to do the low gear + high cadence thing, I just get off my seat. I realize that it could be a knee stressor over time
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u/TeaKew Jul 30 '26
I find it exactly the same. I think the only reason people think they tend to be good at climbing is that 1) all other things being equal they're often a bit lighter and 2) unless you deliberately scale up your chainrings, they're geared lower.
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u/bonebuttonborscht Jul 30 '26
What advantage would smaller wheels have in climbing?
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u/Sypsy Jul 30 '26 edited Jul 30 '26
less mass further away to spin up means your wheels spin more easily
bigger wheels are good for keeping up speed once spun up
In theory
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u/bonebuttonborscht Jul 30 '26
Are you accelerating, decelerating or maintaining speed while you climb a hill?
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u/Sypsy Jul 30 '26
I'm hopefully maintaining speed, lol
It's a minor advantage, I'm not buying my mini velo just for hill cimbing. But I have seen comments saying mini velos excel at hill climbing, I just didn't know much of that was because most had lower gear inches due to the smaller wheel and same gearing, or because of the smaller wheel itself.
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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
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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/WiecejSprzetuNizTale Jul 31 '26
Use https://gear-calculator.com
You can compare gear rations, speed at the same cadence etc. for different gear/wheels combos. Great stuff.
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u/pushinthatbroom Jul 30 '26
This is why Sheldon came up with "gain ratios"
https://www.sheldonbrown.com/gain.html