I'm pasting this from another post I have on here regarding checking speedometer calibration because it relates to gearing and speed. FYI I'm also upgrading my battery system. The stock Himiway battery is a 48V x 17.5Ah. I now have a plug-and-play replacement 52V x 17.5Ah battery which gives me more range. I also have a rectangular 52V x 20Ah battery I'm going to mount on my rear rack and run both simultaneously using a Fusion Battery Blender, which should give me more power (torque) and a lot more range. Stay tuned....lol.
I did another test. See attached. My top speed showing on my KD718 display was 55.8 kph (34.68 mph). My top speed showing on my phone GPS app was 54+ kph (34 mph). I'm saying 54+ kph because my GPS app doesn't display decimals so I'm assuming the speed was somewhere in-between 54 & 55 kph. So being less than 1 kph difference from my KD718 display and the GPS app I think is quite accurate and acceptable. As I said before I changed my settings from being for a 26" wheel size to being now a 28" wheel size. I'm gonna leave the settings on 28" wheel size. I was going to continue and see if I might be able to get a bit more than 34-35 mph but it started raining so the testing was aborted cuz I'm a p**sy and hate riding in the rain....lol. FYI I've got a 48T chainring. If I could get a larger chainring mounted the same as the stock chainring without hitting the frame and getting an extreme chainline I'd really like to use a 52T chainring, which I already have sitting on my shelf. I'd have to mount larger than 48T on the outside of my bracket causing an offset I don't like the looks of.