Testing the Drive Slow Theory

I went to visit my parents over the Easter weekend. They live in Leamington, about a three hour drive from Waterloo.

With that much driving ahead of me for the weekend, I decided I'd test the theory that driving slow saves gas with a little experiment.

The method:

1. Fill up at the FlyingJ in London.
2. Drive to Leamington, driving at or below the speed limit for the entire trip, drafting behind tractor-trailers when convenient.
3. Fill up again in Leamington, noting how much fuel is required.
4. Eat your fill of food: veal, pasta, salad, turkey, potatoes, farmer sausage, wine, ham, gooseberry pie, etc.
5. Drive back to the FlyingJ in London, driving 10km/h above the speed limit
6. Fill up, again noting how much fuel has been added

Observations and measurements:

• Fill up in Leamington: 12.396L
• Fill up at Flying J: 15.976L
• Weight before the Easter weekend: 172lbs
• Weight after: 175lbs

Calculations:

• Difference in gas consumption: 15.976L - 12.396L = 3.58L
• Percentage increase: 3.58L / 12.396L = 28.89%
• Weight gained over weekend: 175lbs - 172lbs = 3lbs

Conclusions: I used 28.89% more gas driving 10km/h above the speed limit back to the Flying J than I did driving slowly to Leamington. I'm assuming that the difference was a result of driving slower; not from gaining weight for the faster portion of the trip.