Buy better tires.
Why is it, then, that a marketing blogger would talk about wanting to reduce fuel consumption? I think it’s because it’s easier to relate to than streamlining other processes you may have in your business or development cycles. It’s something we can relate to directly.
If we assume that all the cars drive the same number of miles, which would be a better investment:
- Get new tires for all the Suburbans and increase their mileage a bit to 13 miles per gallon.
- Replace all the Priuses and rewire them to get 100 miles per gallon (doubling their average!)
That’s right – spend a little bit of money on the Suburbans, and cut fuel usage more than you could by doubling the efficiency of the already-efficient Prius.
Why? It’s because we think in MPG rather than GPM. What does thinking in miles-per-gallon do to our brains that gallons-per-mile would make clearer? Well, here’s the math:
- Let m be number of miles driven by a car…
- Let s be the gas consumption (in gallons) for Suburbans (= m/10)
- Let p be the gas consumption (in gallons) for Priuses (= m/50)
- Let T be the total consumption (in gallons) (= s + p = m/10 + m/50 = 6m/50 = 0.12/m)
So in Scenario #1, we have T = m/13 + m/50 = 50m+13m/650 = 63m/650 = 0.097m
And in Scenario #2, we have T = m/10 + m/100 = 11m/100 = 0.11m
Scenario #1 reduced consumption by 0.12-0.097 = 0.023; Scenario #2 only by 0.01; Scenario #1 is 2.3x more efficient!
This is due to a power-curve relationship early on in the MPG table, where a minute improvement (1 MPG on 10) is a huge percentage improvement (10%) at the front end whereas later-on it’s minuscule.
I thought it was neat 🙂
Original article – http://sethgodin.typepad.com/seths_blog/2009/08/not-so-good-at-math.html