I took 2 bikes for a demo ride yesterday. I rode the Fat Bob 114 and the Heritage Classic.
I noticed both bikes at above 70mph, there is a vibration, that after a couple of miles will make my hands start to go numb.
I don't know if the Heritage had the 114 or the 107.
Is that common on the new M8 bikes?

 

All I can tell you is my son has a 16 Slim and it's like you said at higher speeds. But my hands never get numb, it's just not as smooth running as my King at high speeds. In town and at stops his is smoother. I test drove a new 114 heritage and it felt about the same as my sons 16. On the freeway I like the rubber mount better. Any other time, not a big deal to me.

 

My M8 RK is so smooth at speed I have to be careful I don't take a nap!

 

My 2018 RGU is smooth. At idle, there is a bit of a thrum, and it has a slightly off-kilter nature, but very little actual shaking. Once rpm rises above idle, most vibration goes away and does not return at any higher rpm. My M8 is much smoother at idle than my 2016 Ultra Classic (air cooled) was, but pretty much the same as the 2016 at all speeds above idle.

 

Softail is rigid mounted with dual counter balancers. They tend to buzz at 3k and up, most noticeable on long rides after stopping. My twin cam Deuce did it pretty bad. Touring bikes are rubber mounted so smoother.

 

My Fat Bob had notable vibration in the handlebars when new, and probably would have led to numb hands. I replaced the handgrips with Kuryakyn ISO grips with bar end weights, and it's now glass smooth.

 

 

 

Must be you I've ridden rice bikes with more vibration than my M8, thing so smooth you forget it's a harley.