shocauto.com Blog

“The metric system is a tool of the Devil. My car gets 40 Rods to the Hogshead, and that’s the way I likes it!”
- Grandpa Abe Simpson

Most of us in the US don’t measure fuel consumption in Rods to the Hogshead, but the units we do use don’t make a lot more sense. We currently use Miles per Gallon (MPG), where Europe and Canada measure in Liters per 100km. While the European standard is in metric, which we still won’t accept, and measures per 100km, rather than per one km, there is a distinct advantage to the idea of measuring fuel in volume per distance, rather than distance per volume.

Before I get too technical and lose many of you (too late? oops), here is the quick and dirty problem with MPG. If you actually look at the amount of fuel burned, you would see that the decrease in fuel usage between 15 and 20 MPG is much greater than that between 35 and 40 MPG despite the fact that they are both an improvement of 5 MPG.

So let’s look some graphs, maybe that will help. This first graph shows a plot of MPG to GPM from 0 MPG to 100 MPG. What you can plainly see is that the drop in fuel usage per MPG is much greater at the bottom of the scale than it is at the top of the scale.

Here is a graph that shows the same data, but is scaled to show the MPG range we most of us currently see in our cars:

While the difference is not so obvious in this graph, it is still present.

There is an automotive X Prize out there to build a mass production 100MPG car. The problem with this is that it’s really not as big a jump to get to 100MPG as it seems.

If a truck gets 12.5MPG, it burns 0.08 gallons for each mile driven.
If an average car gets 25MPG, it burns 0.04 gallons per mile.
If a hybrid gets 50MPG, it burns 0.02 gallons per mile.
If an X-prize winner gets 100MPG, it would burn 0.01 gallons per mile.

So, doubling the mileage in for each car (12.5 -> 25 -> 50 -> 100) does not save the same amount of gas. The average cars saves 0.04 gallons per mile over the truck, but the hybrid only saves 0.02 gallons per mile over the average car, and the X-prize winner would save only 0.01 gallons per mile over the hybrid. In fact, the X-prize winner only saves 0.03 gallons per mile of the average car, a difference of 75 MPG, while the average car saves 0.04 over the truck, a difference of only 12.5 MPG.

So why do we use MPG rather than GPM? I suspect its because bigger is better. As fuel economy increases so does MPG. The higher the number, the better the economy. But thinking in economy is also inherently backwards. What we should be doing is thinking in fuel usage. That’s what really matters, right?

And for those interested, Grandpa’s car uses a lot of gas at 504 gallons per mile. By comparison, my smartcar is averaging 40 MPG which converts to:

0.025 GPM
4.9 l / 100km
800,000 Rods to the Hogshead

Notice anything odd about this hotrod?

Those are not velocity stacks, that, in fact, is the exhaust. This hotrod was spotted at the Wings and Wheels show in Osceola, WI this past weekend.

Eight carbs, with the intake and exhaust ports reversed. I doubt there is any real advantage to this, but it sure is cool

I don’t know much about this car other than that it was at the Wings and Wheels show in Osceola, WI this past weekend. It was listed as a prototype and is really, really cool!

If anybody knows more about this car, please let me know because Google is blissfully ignorant on it’s existence.

I went out to dinner with my friend Erik and his wife on Friday, I drove my yellow smart, and he drove his, and what to do you, but we found another yellow smart in the parking lot. Mine’s the one on the right.

In June I wrote a review of my smart fortwo. Since then I have manged to put a few more miles on it and through I’d write an update.

I now have about 6200 miles on my smartcar. Most of those are highway miles from two road trips and a lot of commuting. I’m still putting about 55 miles a day on it commuting.

Issues

So far I have had a couple of minor issues.

- The alarm sensor. Like many other fortwos, mine had a problem with the alarm sensor inside the car. It would go off randomly when there was no reason. The dealership fixed it quickly as a warranty repair.

- Check engine light. The check engine light came on but reset itself. I had the code looked at and it was a very minor error.
- Brakes. My car is starting to vibrate a bit under braking. It seems to brake fine, and the dealership will be looking at it this week.

- Reverse gear. Occasionally, when I’m backing out of my driveway in the morning, the smart will not properly shift into reverse. I have to shift to park and back into reverse to get it to shift. The dealership is looking into that this week as well.

Maintenance

- My tire pressure warning light came on last week, prompting me to check the tire gauge. It turns out one of the tires was 3 PSI low.

- During it’s trip to the dealer this week, it will get it’s first oil change. This will be an early change, since the car is designed for 10,000 mile oil changes. MY dealer is charging $98 for an oil change, which includes synthetic oil.

Economy
It’s a little extreme, but I’ve been tracking every cent spent on my smart. So far, including the purchase, upgrades, and fuel, it’s cost me $15,232. I’m averaging 38.6 MPG over 6200 miles mostly at 65-70 MPH.