I have an old remote control monster truck toy like that. The heavy part with the electric motor and gears is all one piece in the back. Then the battery and the plastic shell sits on top of springs. The part at the bottom of the springs might actually be heavier than what is on top! You could say that the top is the unsprung part.
Back in the 1960’s the Jaguar XKE had low mass wire wheels and inboard brakes mounted inches from the “pumpkin” in an effort to reduce “unsprung weight” and improve handling. With the steel wheels and heavy drum brakes of the time, it mattered big time.
The alternative of forty pounds of iron swinging from the end of a 3 foot half axle took a whole lot of effort to damp it down, especially critical during a race.
Today, standard lightweight aluminum rims, lightweight disks instead of drums and most driving under 100 mph has made that practically irrelevant unless you’re entering your Corolla into Le Mans.
Yes, for most of us non-professional drivers, the reduction in “sprung weight” may possibly make your ride smoother but for those of us who hit the post winter potholes, not so much.
Except for the pothole damage to our “softer” aluminum rims. .
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Weight, does not impact fuel economy as much as people would think.
It’s mainly a factor when you’re trying to overcome your rest inertia that is get going from a stop to moving but once you transitioned into moving and are underway, it’s not an issue.
Just remember the saying, that objects in motion tend to remain in motion. We think this applies to space free of gravity, where you just coast in perpetuity until you run into something, but this actually is true here on earth as well.
The main things that slow you down are aerodynamic drag, and drive train and tire friction.
Here’s a cool thing about physics it takes about 15–30 hp from your engine to move the vehicle along at the posted speed limit on a level highway.
What’s interesting about that amount of power is that it is the same regardless of the weight of the vehicle so if that’s a Honda Civic, it takes about that much power to keep it moving along and if that’s an S class Mercedes, it takes the exact same amount of power to move the heavier vehicle.
This is why it’s no surprise that some of these high-powered V-8 luxury cars can get surprisingly close to that civic in highway MPGs.
If only SUVs and trucks could have the aerodynamics of cars, then they would enjoy similarly impressive MPGs on the highway too.
Seems each new full size truck designs are less aerodynamic.
Manufacturers want to appeal to the segment of the truck purchasing crowd that want a ‘big rig’ appearance.
I had just pulled into a space at a big box store, a Chevy truck, biggest half ton Chevy produced, pulled into the space next to me. Took the driver several maneuvers to get into the parking space then was within 12 inches of me. I pulled out to park elsewhere.
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Weight matters a lot for city stop and go driving.
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If you are doing all your driving at steady speeds, this is generally true. Things like wide tires and bigger vehicles do have a measureable effect. Weight does matter for rolling resistance but, as you post, it is smaller than aero drag.
But we rarely run a steady speed these days, even on a highway, because of traffic. So weight matters, quite a lot, to fuel economy. Vehicle weights, even for similar sized cars, has grown over the last few decades. Better crash protection, required and preferred equipment added to cars over the last 3 decades has pushed that weight up. All that weight takes fuel to accelerate it. If there is no hybrid system to collect some of it, that speed is turned to brake heat. Those big wheels we like, act like 4 flywheels using fuel everytime we accelerate.
If advances had not been made in engine and driveline efficiency, we would be seeing reduced mpgs, not increased.