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2 posts • Page 1 of 1
I am thinking of building a town bike using the Patterson 2 speed crank ( http://pattersonbike.com/ )
The cranks come with a physical 28T chainring with 1.6:1 overdrive given it a 45T virtual chainring.
45T is a little too low, and would rather more for the hilly areas I live in, so I can buy an adapter for a 130BCD chainring.
Now this is where it gets tricky - the smallest 130BCD chainring is 38T, which would give me a virtual gear of 61 (?)
I am of reasonable fitness and ride recreationally. The rear cogs are available in 16, 17 and 18, which would you recommend and why?
Gearing wise, with a 2 speed i think most people would suggest setting it up with the overdrive as your "everywhere" gear, and the 1:1 gear as a bailout for steep hills. So for that, 45-16 might be a smidge low, depending on your preference. I have a 46-16 on my singlespeed and it's only just barely tall enough for the flat, but i prefer a really slow cadence, and the upside is that gear works really well for climbing.
An effective 61t chainring with an 18t freewheel is an 89.1" gear which is pretty big, the 45-16 is 73.9" and as an example a 52-17 is 80.4" and even with my preference for grinding rather than spinning that is comfortable up to about 40kmh. As you're saying it's for a town bike i can't imagine you would be wanting to sit on 40 that much.
I'm curious about the rear cogs, if your wheel takes a standard freewheel then while those 3 are the most common sizes you can quite easily get a few more. With the "61t" a 20t freewheel gets you an 80.2" gear, and 21t is 76.3", which is slightly taller than the 45-16.
Of course that's just the top end, there's also the matter of deciding what you would be happy with for your low gear. You can tinker around with the numbers yourself at this link. http://sheldonbrown.com/gears/
When man invented the bicycle he reached the peak of his attainments- Elizabeth West.
2 posts • Page 1 of 1
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