I need a little help calculating differences with changing cogs and the increase in speed on my recumbent trike. I'm trying to use a phone app and not sure if it's correct. What I'm looking at is if I change my rear cog from a 20t to 16t the increase in speed. Specs... chainring 42t (170mm arms) 20t cog (current) 20x1.75 tires I get 15.2 mph max with my cadence. The app says 19.1 mph with a 16t. Does this sound about right?

Thanks!