36 or 38 tooth rear
 

What sort of reduction in RPM's am I likely to get switching from a 42 to a 36 or 38 tooth rear sprocket? I have the 17 front.

42/17=2.47
38/17=2.24
36/17=2.12

But it all depends how much wind you hit. Will your bike climb hills at speed on a windy day with a 36 rear? I don't know?

I don't think I could pull a much smaller rear sprocket. 40 is probably the lowest I would go.

Allen