Originally Posted by
wheelreason
Why do we need anything other than the ratio between the the chainring and the cassette sprocket here? And more importantly, can I score some of ya'lls stash...
I will say that there is a difference in friction (and wear), all be it small, and bigger is better in both cases.
When I'm looking at gearing available - for instance most recently when I was looking at Sram AXS gearing options - all I did was do a simple calculation of the front/back gear ratio of the highest gear and the lowest gear and compare that to the high and low gears I've been satisfied withor that my wife has been satisfied with. Whether the low is as low or lower is the most important part. The high gear just needs to be close.
I really don't know (repeat:
I really don't know, not implying that nobody would know) why one would have to be more precise than that. Oh, and crank length - for me - 170-175 - is A-OK and I notice no difference, not only in how it feels, but would be meaningless for how the gearing works. Repeat: FOR ME. I have no doubt that people who compete and have the motor to be truly competitive would want to optimize these things, but for me and probably the other 99.9% of enthusiastic riders and weekend competitors... ? Probably not.
I used to play around with the online calculators, but they didn't give me any more functional information than a simple division exercise.