On my M8 FLHXS 2017, I find the 5th and 6th gear to be on the high side ratio wise. At 100 /hr , rpm at 3000 on 5th and at 75 /hr on 6th. also 3000rpm. If I remember on my FLHCUI 2017, ratio was lower by 500 rpm. 75m/h at 2500 rpm. Wonder why MoCo put a higher ratio ?

 

Can easily look up gear ratios on Harley-Davidson website.

When I test Road a M8 SG I thought the gear ratios were different than my 14 SG. But they are the same.

 

I think the final drive ratios from 2009 and newer are all the same, and on going to the M8s too.
Should run about 3000 RPM at 75 MPH in 5th gear, and about 2500 RPM in 6th gear. That is
about what I get on my 2014 FLHX Standard as far as RPM in 5th and 6th gears. A different
rear tire size will change your RPM verses speed some.

John