Saturday, December 5, 2015

How many mpg???

On my way to work yesterday I discovered someone had left the gas tank nearly empty. A gizmo on my dashboard told me I had only 60 miles left...for my 76-mile commute! (In reality, the Mazda 3 has a “reserve” tank of about 2 gallons, so I was in no danger of being stranded.)

I was already late to work, so driving sub-65 mph to maximize fuel economy wasn’t an option. Still -- even with a “cold” start, morning traffic and several stoplights to negotiate -- I was able to roll into work 38 miles later having gotten 40.8 mpg!

That left another 38 miles to get home...and my fuel gizmo told me I had just 27 left. (I burned off 3 of those driving 2 miles back to the highway!) So how would I stretch the remaining 24 into 36? 

At the stop sign I looked to my left and noted a lumbering “semi” (tractor-trailer) headed my way. He was going slower than the posted speed limit, but I wanted to try this experiment anyway. So I let him pass, pulled onto the highway behind him and set my cruise control.


We were going just 58 mph! He must have had his own cruise control, because that speed never varied one mile per hour either way, except when we came to a stop light. (And there were four of those.)

I reset the fuel monitor. In the previous two miles -- after another cold start, several sharp turns and a stop sign or two -- I had achieved an unremarkable 28 mpg. But now I had dozens of miles ahead of me, a relatively straight road, flat (if not slightly uphill) terrain and a tractor-trailer knocking down the wind for me! How much better could I do?

We were closer than I wanted to be. (So close that I called us "we"!) I couldn’t see where "we" were going! I regularly drove this close in heavy freeway traffic. Even at 80 mph! But now it seemed almost sinful. "We" had plenty of open road. I could easily have a whole lane to myself. (He must have thought I was crazy...if he knew I was back there!)

Since we were only going 58 mph, I thought it was “okay” (just this once) to “fudge” a little on safety. I normally maintain at least “two seconds” of distance between me and the guy ahead of me. But if I backed up that far on this trip, my gizmo told me I would lose all benefit of slip-streaming. So I maintained barely half that distance. That meant I had to keep my eyes on the road! (And on the back of that truck!) I also constantly had to fiddle with the cruise control to maintain the “perfect” speed and distance between us.

Was it worth it? My fuel efficiency shot up 12, 14, even 20 mpg! Pulling into the gas station 36 miles later (on an “empty” tank), I was elated to see I had achieved an astonishing 60.3 mpg on the highway and 55.2 mpg overall! 

Would you be willing (or comfortable) to drive behind a moving “wall” to get those kinds of numbers? (I imagined myself getting “squished” between two semis! Or maybe hitting a tire or other object in the road. Or slamming into the back of that truck if he had an accident!) It was just too easy for me to drift "too close" to him whenever he slowed down. Keeping a “safer” — if not an altogether “safe”— distance between us was just too much work!

But what if I had a technological assist?

High-end Mazdas (alas, not this “entry level” vehicle) come with adaptive cruise control, allowing one’s car to maintain speed and distance behind another vehicle (up to 90 mph). Cars can dart in and out of your path, speed up or slow down, and your vehicle will adjust automatically to maintain a pre-set speed and distance (or match their speed, whichever is lower). With that technology I could find the “perfect” distance behind a semi, press the button, and my 60-ish-mpg fuel efficiency would be served up almost automatically! 

Even without drafting I get mileage in the low- to mid-40s in this new Mazda 3...if I’m careful to go the speed limit!

Still, it’s fun to know that this car can get 60 mpg at roughly 60 mph with a little extra effort and a lot higher blood pressure!

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