Gear ratios

Bluestoesonnose

Building up a single speed for the winter (yeah, yeah I know...)

Anyway; just wondering what ppl are using for hilly areas, I live on the edge of Dartmoor so I'm going to have to live with the fact that I'm going to be spinning like a loon in sections but... I seem to get on ok with 42:20 gearing on all but the steepest hills. The only issue is it seems that most single speed rear sprockets come in 16 tooth or 18 tooth. Am I correct in believing that the equivalent gearing would be: 38:18 or 34:16 both of which have a 2.1 ratio, or does the wheel diameter (700cx23mm) also matter?

Cheers

earthvspace4XTuUWcX

Nothing wrong with a single speed for winter, I run a 47X18 but avoid big hills! You might find this gear chart handy for a quick reference, but yes, the options you quote will give a similar gear ratio.
http://www.ctc.org.uk/sites/default/fil ... ratios.jpg

Bluestoesonnose

Cheers, I don't think I'd get up 90% of the hill on Dartmoor with a 47:18

JayKosta

If the 'gear ratio' is the same, then the 'feel' while pedaling will be the same.

I do suggest doing some test rides on the flat using a 42:20 combo.
It is quite low and might not be satisfactory for regular use.

Jay Kosta
Endwell NY USA

Bluestoesonnose

Hi Jay,
Been riding 42:20 all week on my 8 mile commute to and from work, it's a little low on the flats but I can get up all but one hill so it's about right.

Cheers

hypster

Are you using a rear cassette freehub with a SS sprocket and spacers? If so, On One do their Groove Armada sprocket 13-22T for £14.99.

drlodge

It may not help, but I had to "limp" home with my RD cable snapped. I opted for a 21T rear with 34/50 front which gave me a 50-21 for the flat (was a bit low but actually perfect as there was a headwind) and 34-21 for the hills.

42-20 = 55 inches
50-21 = 63 inches
34-21 = 43 inches

So I'd say 42-20 is about right - too low for fast flat or downhill, and too high for steep hills. But its in about the right mid point for the best overall compromise.