Yes, back in the 1980s and earlier, there were some larger "wheel shops" that did their own work, putting particular "centers" into wider "rims", for example. Not unlike the "reverses" that were done to many wheels that were popular on some cars. "Chrome reverses", for example, back before the aftermarket wheel industry became so large.
These companies had "rims" and you could put whatever you needed into them as "centers". But somewhere in the later '80s, they stopped doing that. At least the big wheel/axle place in Dallas, tX. Their reply, when questioned, had something to do with product liability. So they then only sold "factory made" wheels after that.
Remember when Dodge was the first pickup truck to offer 20" wheels, and Chevy/GMC didn't? It was mentioned on a car show that Dodge upgraded their braking systems to handle the increased rolling inertia of the larger wheels. A year or so later, GM did likewise on their next body series.
Pick up one of the late model pickup truck 20" factory wheels. in alloy, it weighs very similar to a 1988 steel C-20HD bare wheel. Add a 20" tire to that weight and it's very heavy, compared to what we had in the 1970s. I had to ship a 1988 K-20HD wheel and tire back then, it was over 80 lbs.
Air flow management is one of the "tricks" used to make modern light-duty trucks as fuel efficient as they are. Having the wheels "out to the edge" help with that, especially on the front. Then getting more of the air through the radiator, via the air dams under the front bumper, too. Plus the smoother edges on the hood and fenders. And that "laid-back" windshield! Augmented by drivetrains that allow for 1700rpm @ 70mph on the road, but the aero package is where the highway mpg come in.
THEN, there's the tires. Tread design, rubber compounds, and internal bits. Shorter sidewalls help here, just as the supporting players in the rest of the tire's design. Reduced flex which equals less power consumption. By observation of many TireRack spec tables on tires, many of the 20" tires usually start with 8-9/32" of tread depth, which means 6-7/32" of usable tread before you hit the wear indicators. Whereas the tires our cars came with had 11/32" of tread on them, but wore out sooner.
Powertrains and management thereof are important too. In a typical 8=speed, low gear is between 4.5 and 4.9, with 2nd gear being about 2.5 (similare to the old 3-speed's 1st gear), with 'top gear OD" still being about .70. So plenty of gear for a low-throttle-input start, then shifting to the higher gears quicker with the same throttle setting. In a modern 8-spd TF, just think about speeding up a bit, and the next gear down puts another 300rpm on the tach, for accelereation with almost no throttle input. End result, no "power mixture" needed for better emissions and fuel economy. By my observation and experiences.
But for ALL of these things to work, the "aero package" has to work well. So that as little throttle as is possible is needed to run the vehicles down the road on the highway at 75+ mph.
Enjoy!
CBODY67
