Lots of choices, but pricey. I'm not sure that I want to drill a bunch of holes under my car to mount the back side of Dzuz fastener; rather use existing bolts if possible. I'm too new to post links on this forum, but do a search on Dzuz fasteners.
Gerhard Plattner: "The best attitude is to consider fuel saving a kind of sport. Everybody who has enough money for a strong car, can drive fast and hit the pedal. But saving fuel requires concentration, self-control and cleverness. It's a challenge with the nice effect of saving you money that you can use for other more important things."
The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.