Thursday, June 9, 2011

Response to Jeff -- slowing down does save gas

I wrote in a recent blog that slowing down does save gas, and got a spirited disagreement from Jeff Davis. You can read his comment attached to that blog.

I would certainly welcome more comments on this topic. I can say with certainty that my view is not widespread. Most drivers in SE Michigan drive as if the posted speed limit is the minimum speed not the maximum. And, most drivers here view those who drive under the posted speed limit to be idiots and a menace to normal drivers.

Whether or not driving slow or fast affects gas mileage does not appear to be a major concern. Most drivers seem intent on getting there -- as fast as possible. My blog was simply to point out that all the crying about high gas prices does not seem to translate into any thought of slowing down.

So Jeff, you are correct in your thinking that most drivers would agree with you that drivers who are going slow to save gas should get out of their way.

You are also correct, Jeff, when you say that many cars have computers that optimize gas mileage,. However, your estimates that 99 percent of all cars have such computers and that all those computers save gas regardless of speed is overly optimistic.

Cars manufactured after roughly 2007 have better gas-optimization computers.

It also is true that they will give you the best gas consumption possible for the particular speed you are driving. But it is not true that they will give you the best gas mileage you can get at whatever speed you drive.

All vehicles have a "sweet spot." This varies from vehicle to vehicle and depends on many different factors. But, in a nutshell, it is the speed for that vehicle that will regularly provide you with the best possible gas mileage.

For most cars, it is somewhere between 52 and 65. It is rare to find a vehicle that achieves its best mileage at a speed over 75.

You do not have to take my word for it, you can prove it to yourself. If you have a regular drive that you make, do several test runs at 55 and 70 and carefully check the gas consumed each time. I usually do this by filling up as I start and then again as I end the trip, and write down the total gallons used and the miles traveled.

In my own case, I regularly drive from one side of the state to the other. I can take the freeway, where I am forced to drive at 70 or be run over by the truckers; or I can take country highways where the speed limit is 55.

When I take the freeway, I get there faster, but my mileage is around 25 miles per gallon. When I take the back roads, it takes a bit longer (20 minutes) but I get around 32 miles per gallon.

What do you want? Early arrival or better economy? Your choice.


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