Tonight I tried to figure out if my hub-geared bike is a sane choice USING THE POWER OF MATHS!
For example, this guy sounds pretty pleased to have had a “25-12 tooth cassette and 30 – 42 – 52 chainrings” to get up the hills of Devon. That means his “easiest gear” used a 30 tooth sprocket at the front and a 25 tooth sprocket at the back, and so one turn of the pedals turned the back wheel 1.25 times.
My hub gear bike came with a 44 tooth chainring and a 20 tooth sprocket at the back – a ratio of 2.2 by itself. But the hub gear itself provides a ratio of 0.53 (easy) to 1.61 (hard). So the combination means that my easiest gear ratio is 1.16. Looks like I should have an even easier time uphill than Mr Derailleur.
What’s more, I think his racing bike has larger wheels (700mm = 27.5″) than mine (26″) which means that each revolution of his wheels makes him go further. Good news for him on the flat, but bad news for his hill climbing. To be truthful, I can’t figure out whether those measurements reflect the distance to the wheel rim or the outer edge of the tyre.
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One thought to “Gear ratios”
Hi Andy, 700c tyres are for 622mm diameter rims, 26″ wheels have 559mm.
have a google for “gear inches” for more talk of these matters. (mainly by singlespeeders ;o) )
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