MAX Update No. 84: Speed Kills (Gas Mileage)

http://www.motherearthnews.com/green-transportation/100-mpg-speed-kills-gas-mileage.aspx

In my 7,500-plus mile adventure in MAX this summer, one lesson really stands out: Haste Makes Waste.

To make a long story short, when George Voll and I drove our high mileage cars (that’s George’s car in the background) from his home in Indiana to the MOTHER EARTH NEWS FAIR in Pennsylvania, we drove various legs of the trip at various speeds. By driving in formation and scrutinizing each other’s fill-ups, we got two-heads-are-better-than-one confirmation of our mileage.

The above photo shows my side of the fuel pump, just east of Columbus Ohio, after our 100.4 mile, 45 mph run from Cleveland. I confirmed speed and distance with my GPS, but for most of the trip George’s diesel Metro was the pace car.

We had driven that leg at 45 mph for three reasons; first, George had never driven a hundred miles that slowly and didn’t know what his mileage was down there; second, 45 mph was the minimum speed when the Auto X Prize did its oval track “race” last year and we wanted to measure ourselves against that benchmark, and third, it was raining hard when we left Cleveland and it’s uncomfortable to drive MAX fast in the rain.

MAX and Diesel Geo Metro at Gas Station 

Mercifully it quit raining as we approached Columbus, so I was able to pack up my motorcycle rain suit (it’s in the black Triumph bag sitting on MAX’s “trunk”) and wring the rainwater out of my earplugs (no, I’m not kidding — the rain suit keeps my body toasty but rain blows in between my helmet and my ears, and if there’s lots of rain, my foam ear plugs soak it up). After this ordeal, my rain suit stayed packed and my ear plugs stayed dry for the rest of my trip — to Pennsylvania and all the way back to Oregon afterward. But I’m drifting off subject; I’ll write about rain some other day.

Anyway, back to the fuel pump. George and I looked over each other’s shoulders to verify we couldn’t squeeze another ounce into our tanks, and if you’ll look at the fine print on the pump you’ll see MAX sucked up 0.891 gallons, which works out to 113 miles per gallon. I generally expect 115 mpg at that speed, but it was cold and raining and neither cold nor rain help mileage. George got 94 mpg, which is spectacular for a four seater in any conditions, but I’ll save that for another story. This post is to show that I only have to do one thing to get MAX into the hundred-’teens on the freeway: drive at the low end of the speed limit instead of the high end of the speed limit. No hypermiling, no coasting down hills in neutral, no drafting, no waiting for clear warm days — just driving as slow as the law allows instead of as fast as the law allows.

Now I’ve had better mileage results in the heat of competition and so has George (he won the diesel class at the 2011 Green Grand Prix at 106 mpg) but we’ve also had worse results. In MAX’s case, mileage drops about 10 mpg when speed increases 5 mph, and my biggest challenge on long drives is keeping my speed from creeping up.

Since it’s an easy target to remember (and since people always ask), I shoot for 100 miles per gallon in my travels. 115 mpg at 45, 105 mpg at 50, 95 mpg at 55 miles an hour, it’s simple: I keep my cruising speed between 50 and 55, and if I get less than 100 mpg on a fill-up, I slow to 50 until I’ve got my mileage back up to three digits.

Or at least that’s the theory. In practice, well, if I’m getting 100 miles per gallon at 52-1/2 miles an hour, it’s hard to resist going 55. In the rarified atmosphere of extreme high mileage, reducing mileage by 5% doesn’t feel like it hurts much, and indeed it doesn’t; the difference between 95 mpg and 100 mpg is modest — a gallon every 2000 miles.

But at 60, MAX’s mileage has dropped into the 80s and I’m starting to feel some pain, and by 65 mph (where MAX gets roughly 75 miles per gallon) I’m feeling like a hypocrite, and at 75 miles an hour — yes, I did do a measured two hour blast at 75, gunning across South Dakota — mileage was deep in the 50s and I was giving myself the same pursuit-of-knowledge rationalization that I’d probably use if my job involved testing eye shadow on bunny rabbits.

Clearly I’m getting too emotional about fuel economy…or am I? My obsession with conserving fuel in MAX has taught me good lessons, lessons I can use no matter what I drive. Percentage-wise, my work van’s fuel economy suffers similarly from speed — every extra five miles per hour costs me about two miles per gallon, and two miles per gallon doesn’t sound like it’s worth bothering with — but thanks to MAX’s good influence, I’m driving the van at 55 instead of 65 nowadays, and it does makes difference.