While I appreciate all the advice and riding tips, I've been doing this for 39 years, and I've owned many sport bikes too. I'm aware of what's happening and why. And what to do about it. It's that I ride a 900+ pound, steel frame, Yamaha cruiser. I can hang with sport bikes on the twistiest of roads. It's the high speed sweepers that my bike doesn't like; it has a tendency to "wallow" through sweepers above 60 mph. (Frame flex?) Add 70+ mph traffic all around you, while going down hill, and off camber sweepers with rain grooves? That's when the fun starts. I'm just making an observation and it's nice to know I'm not alone.
And I hear you about those steel grated bridges. I live in Alameda, [an island with lots of steel grated bridges] and learned to ride at 13 on a Honda Trail 90 with big old knobby tires. It was an adventure every time I left the island but I learned at an early age about riding over challenging surfaces.
Probably frame flex, tires, steering geometry, and suspension. You should not be able to feel any flex if you shake the bars. It's hard to explain what this feels like, you have to ride a bike that has flex and do it - then ride a bike that doesn't have flex.
The second bike will feel like a single block of metal. Even then, you may still get weird handling. My W800 has a special frame that Kawasaki revised in the 2019 model year. It looks the same as previous ones, but they increased tubing thickness. It has nearly no flex, but the bike follows grooves. It does this probably because of the steering geometry.
Tires appear to change this, but not much.
It's also a handful on roads that are paved badly, but you just have to hang on (but not too tight).
With the above being said - none of this has impact on *traction* - the only time you lose traction on crappy roads is if the bumps are so bad that they send your tires into the air. And this is really only a factor when you are turning. Then what happens is that the bumps throw you into a different line and you have to correct.
