[kach22i]

Originally Posted by RedDevil

4WD cars roll more smoothly over speed bumps than 2WD cars do. But in winter I'd rather have 2WD with snow tries than 4WD with all season tires. And you lose about 10% in FE.

Winters in SE Michigan are marked by many freeze/thaw cycles, perhaps the most in the world. This accounts for many of our pot holes and results in a very slushy winter. Our roads spend most of the winter being wet as a result of excessive use of salt (cheaply mined locally).

Snow ties are designed to grip and hold snow, the snow on snow bond accounts for snow tire traction.

All Season tires, rain tires and mud tires conversely are designed to remove water from the grooves and fling it out of there, thereby preventing hydroplaning (or mud sliding).

Snowy Winter = Snow Tires

Wet Winter = All Season Tires

Just say'n not all winters are the same.

Originally Posted by RedDevil

The wheels going over a speed bump travel a greater distance than the wheels on a flat surface.
When they are not driven they temporarily speed up, forced forward by the mass of the car. But the driven wheels don't speed up much as they are connected to the engine, which tries to maintain its revs and has a large rotational mass anyway - so the car has to slow down a bit; especially on the upslope.

With 4WD this effect is spread over 2 axles, so when the front wheels hit the bump and slow the car the rear wheels resist the slowing down and force the car over, and likewise when the rear wheels climb the bump the front wheels will pull it over.

There are formidable speed bumps where my parents live, and when my dad bought a Subaru the way it kept going at steady speed over those speed bumps was the thing that impressed me most.

With a velomobile there is very little rotational mass in the wheels, even the driven one. If it also has smooth wheel travel it could float over speed bumps as if they were hardly there.

Interesting theory, but isn't torque on the wheels an important factor?

My rear wheel drive biased AWD Infinity G37X Coupe (automatic) has torque vectoring AWD and prior to having the worn tires replaced I was able experienced their correction on a wet road - it works well. The AWD launch is exceptional, takes off like a big cat on all fours. One thing I can say, it is exceptional over bumps, but that might be because it is just as much a luxury car as a sports car.

Just saying it is perhaps the torque on the wheels you are noticing.

If I recall correctly the Geo Tracker 4WD I drove for 20 years, in 2WD over railroad tracks the rear end would lift a little, but in 4WD it stayed planted and was more stable. Maybe it was the torque to the front wheels? It was a stick shift and I usually slowed down and coasted with the clutch depressed, so I don't see how it could be torque. Wish now that I could go back in time and test out an A to B comparison.

Originally Posted by RedDevil

There are formidable speed bumps where my parents live, and when my dad bought a Subaru the way it kept going at steady speed over those speed bumps was the thing that impressed me most.

Perhaps it is the type of AWD the Subaru uses that makes a difference.

Subaru Employs Four Distinct Types of AWD Systems
https://www.qualitysubaru.com/symmet...-explained.htm

Torque vectoring
https://en.wikipedia.org/wiki/Torque_vectoring

As technology in the automotive industry improves, more vehicles are equipped with torque vectoring differentials. This allows for the wheels to grip the road for better launch and handling.

I've skimmed a couple of articles touching on Torque Vectoring, (example), and ride comfort seems to be overlooked compared to stability and other performance issues (handling).

As far as academic papers, the last sentence in the following synopsis looks promising.

2016
A comparison on optimal torque vectoring strategies in overall performance enhancement of a passenger car

Among the torque vectoring differential strategies, stationary clutch in handling and four-wheel drive in fuel consumption as well as ride comfort have better operation and more enhancements.