Hypermilers are champs at saving gas

A few years ago I was managing an experiment aimed at determining whether it was practical to power cars with hydrogen, instead of gasoline. Most of the cars were small gasoline-engine SUVs which had been modified to burn hydrogen.

Hydrogen, at automotive operating temperatures, is a gas that must be compressed and stored in high-pressure tanks. The tanks are made of carbon fiber. They look a lot like very large scuba tanks. A hydrogen storage system small enough to store aboard a car can only hold enough hydrogen to match the energy content of about four gallons of gasoline.

So, even if a hydrogen-burning internal combustion car could be made as efficient as a normal small SUV, it would only be able to run about 80-90 miles.

To improve the range of the hydrogen SUVs, we used hybrid engines, rather than straight internal combustion engines. Hybrids are programmed to turn the engine off when the car is stopped in traffic. They use the brakes to charge the hybrid (traction) battery and they run on energy from the battery when possible. With a hybrid engine, our drivers routinely got about 120 miles per fuel fill.

However, one driver, RT, was getting even better mileage. He usually brought the car back to the fueling station after 140 miles. One time, when he had taken an unexpected midday detour that increased his driving distance, he made it to almost 160 miles. I’m not sure the car would have gone another hundred yards on the fuel it had left when he returned.

I asked RT how he had done it. He introduced me to the concept of “hypermiling.” Through his driving techniques alone, he had driven about 33% further than our other drivers on the same amount of fuel.

Hypermilers are drivers who enjoy the sheer challenge of finding out how far they can stretch the fuel they use in their cars, no matter what fuel type they’re using. RT viewed his effort to get better mileage than everyone else as a fun competition.

Despite its excellent results, hypermiling isn’t for everyone. It takes time to plan ahead and can require some habit changes. RT would plan his routes in the morning for the entire day, with the specific goal of avoiding traffic and hills. He would commute to work a half hour early and home a half hour later, just to avoid traffic. He was an early user of GPS maps even when he knew exactly where he was going, because the GPS systems warned him about traffic congestion and provided alternate routes.

RT would overinflate his tires a little, which reduces rolling friction. It lowers tire life and safety a bit, but since he was also making a serious effort to keep his speed around 45 mph most of the time, he wasn’t worried about getting into a high-speed accident. Maintaining a consistent speed and going below the speed limit both improve mileage substantially. A hypermiler’s ideal speed is probably around 40-45 mph, where most cars are able to run at their lowest engine speed in their highest gear before stalling.