Thank you for taking the time to give that explanation and the research. I am very impressed. I am not mechanically inclined so thank you for explaining it in a way that is easy to understand. What, if anything, should be done? As I said earlier, I did experiment with manual down shifting, yesterday, and eventually settled on S2 mode, which made it better.I have researched and can't find out exactly what is happening when we lug the engine. It's not in my old IC Engines textbook, nor in others I can find online. What you can find is people saying "it's the engine working too hard," which is a very unsatisfying answer for an engineer. It is not pre-ignition, because you can hear pre-ignition (knock), but you can't feel it. I have 3 hypotheses:
1. I suspect it is the collapse of the oil film in the conrod & main bearings, leading to the shaking. The way journal bearings work is (we'll use a stationary journal) the rotating portion "climbs the wall" and the closest point to the journal isn't straight down, but is towards one side of the journal, towards the direction of the motion. If we look at a main bearing end-on, if the crankshaft rotates clockwise then the closest point to contact will move from 6 o'clock towards 3 o'clock. The film thickness is proportional to engine speed and inversely proportional to load (high speed and low load = thicker film). Maybe that film gets too thin and we feel the crankshaft moving around in the bearing.
2. Another hypothesis is that with the thinner film thickness (journal bearings are running on a thin film of oil) the conrod bearings get slop in them. The motion is always confused on these since the load reverses. So maybe that's what causes the shaking.
3. My last is the simplest in that when the engine slows down we feel the piston throw more. The load is higher so the piston is pushing harder and we fel the back-and-forth motion more. This one seems the least likely to me.
I bet that real engine design engineers know the why of this but if they've published stuff on it, it isn't easy to find amongst the noise of unsatisfying information on the internet.
Worry less, ride more.
Yep, reason I wear bluetooth ear buds and listen to music....If I didnt wear ear buds, I couldnt stand the noise any of my bikes make (2007 c50 boulevard with 101,000+ miles, my 2013 nc700x with 57,000 miles, and my 2009 Kawasaki klx 250sf with less than 6,000 miles-kept in storage in florida when I go on vacation down there)....all 3 engines make a different noise and all are stock exhaust so the exhaust isnt louder than the engines.Agree 1,000,000%
I am on an NC/CTX facebook page, always same thing. "My motorcycle makes this noise" I've never seen another group of folks worry more about the noises their motorcycle makes than those who ride these bikes. The irony is I would put them up as some of the most reliable bikes ever made.
What is described here in this thread is no doubt the engine lugging in low rpms from being in a higher gear than what is needed for that particular environment.
If engine lugs, gear down and go on. Stay out of D mode if on a DCT and the lugging bothers you. D mode sucks. Sport Mode and override with the + button if you want to shift a little sooner than standard Sport mode shifts. Or...if you are on a newer DCT bike with the 3 different Sport modes, I've found Sport mode 1 is about perfect for where I want it to shift under normal driving. D mode is completely useless to me.
My dad worked as a Honda mechanic when he was young, he told me a story about asking his boss about a noise a bike he was working on was making. His boss listened to it, said it was normal, then said "Son, engines make noises. It's the performance we are after." Will never forget that saying.
If you pay attention to every tiny noise, overanalyze, worry, stress, be paranoid about every little thing, you can't enjoy the bike the way it's meant to be enjoyed. Trust me, if something really bad is going on with your bike, it won't be questionable as to whether it is normal or not, it will be apparent.
Worry less, ride more. Right to the point. I like it.