Originally Posted by
HTupolev
Teeth on the front chainring divided by teeth on the rear cog. 52/20 = 2.6.
It sounds like your issue is that the gear is too low, where you're turning the cranks quickly and having a hard time keeping resistance on the pedals. For this, you want a higher ratio, either a bigger chainring or a smaller rear cog. A 52T chainring is already pretty big; you could make a large difference by using a cog a few teeth smaller in back.
For instance, if you switch to a 17-tooth cog, you'd have 52/17 = ~3.06, which is about 18% higher than your current gear. So you'd be going 18% faster for a given pedaling cadence.
One more thing! About the size of cog, let put teeth number sizing aside and let look at the cog where we insert it in the wheel, are all size come in same or they comes in different size? Even though I'm looking for 17 t. How do I know my size of rear cog so that I can get smaller teeth but same size of the cog.