Go Green: Drive a Porsche!

No really, it's true.

This Porsche 911 gets better gas mileage than my 4 cylinder family sedan!

I'm as shocked as you are. And I'm wondering how I can convince my boss that my next company car should be a 911, so I can save the company money, of course...

Seriously though, German ex-racer Klaus Niedzwiedz proves, once again, that how you drive is as important as what you drive. He was able to hypermile the 3.6L, 345hp sportscar exactly 400 miles (648 kms) on a single tank of gas through city streets, over country roads, and down the Autobahn... all while maintaining an average speed of 52 mph (84 kph), with his top speed being 81 mph (131 kph).

That works out to 42.2 miles per gallon (Imperial), 35.1 mpg (US), or 6.7L/100km.

That's astonishing!

It doesn't hurt that the Porsche employs some high-tech engineering like direct injection, as well as a 7-speed PDK gearbox which enables you to drive 130 km/h while keeping the engine revving under 2000 rpm.

Source.

Speed matters!

For the sake of science, I've been making a nuisance of myself over the past month and a half. How so? By sometimes driving exactly speed limit... aside from the occasional Prius, I felt like I was about to be run into more often than not. Why was I doing this? Read on.

Common sense dictates that driving slower uses less gas! It's simple logic... if your engine turns less RPMs, then you are therefore pumping less fuel through it and creating less power.

But, exactly how much does slowing down save? (Or conversely, how much does speeding up cost?)

Over the last little while I've been keeping track of how my speed affects my fuel economy. Using a Scan Gauge (an essential tool for all hyper-milers and anyone concerned with saving gas) I've been able to verify just how much (or how little) fuel I use during my daily commute. Unfortunately, there's far too many variables involved in my entire commute to give anything close to accurate numbers for comparison.

However, there's one stretch of exactly 16.0 kms which is generally congestion free. Many mornings I can turn on the cruise control and not have to touch a pedal for the duration. This doesn't always work though, and from time to time my test was binned because I had to either slow down or speed up to avoid getting into, or causing, accidents.

This stretch includes a few curves in the highway, 3 underpasses, 2 overpasses, one long uphill, and another downhill section.

I ran many tests at varying speeds, alternating randomly between 100kph (the posted speed limit), 105kph, 110kph, and 115kph. The speed driven on any particular day was chosen randomly. The randomness was to prevent any one factor from unduly influencing the results. Things like aerodynamic drag (tried not to spend too much time behind any other cars on the highway), temperature (it was marginally warmer when I started running these tests), the amount of gas in the tank (full vs. empty, different weight), etc. were hopefully negated by averaging out multiple tests over nearly two months of trials. Results that were inexplicably high or low (severe headwind/tailwind perhaps) were thrown out.

Below are the results of 5 different trips at each speed, taken on entirely random days over the last 6+ weeks.

100 kph:
6.8L/100km - 6.5L/100km - 6.4L/100km -6.4L/100km - 6.5L/100km.
Average: 6.52L/100km

105 kph:
6.8L/100km - 6.7L/100km - 7.2L/100km - 7.0L/100km - 6.8L/100km
Average: 6.9L/100km

110 kph:
7.3L/100km - 7.2L/100km - 7.6L/100km - 7.2L/100km - 7.4L/100km
Average: 7.34L/100km

115 kph:
7.8L/100km - 7.7L/100km - 8.1L/100km - 7.9L/100km - 7.7L/100km
Average: 7.84L/100km

So what does speed cost?

Driving 5% faster than the speed limit costs 5.9% more in fuel.

Driving 10% faster than the speed limit costs 12.6% more in fuel.

And finally, driving 15% faster than the speed limit costs you 20.25% more in fuel!

I'd like to try higher speeds to see exactly how much fuel consumption increases with every 5kph, but there are consistantly police along this particular stretch of highway as well, in at least four different spots, so going any faster for the sake of this blog just isn't worth it.

The increase is definitely steep though. Aerodynamic drag increases exponentially with speed, and therefore increases fuel consumption sharply. Looking at my numbers above you can do the math and see that 20% faster than the 100kph speed limit will cost roughly 28-29% more in fuel.

So, is driving fast worth it to you? I suppose it depends how late you are.

Or how much money you want to burn.

Save Fuel By Driving Less!

That's the brilliant advice offered by Toyota on their corporate blog. Seriously, they've got some pretty intense, hard-hitting journalism there. I never would have thought that not driving my car uses less fuel.

In all fairness though, they do make one or two valid points... things that not everyone may think of. In that same blog posting they link to an earlier article about "hypermiling", which is the practice of adjusting your driving habits & style to improve fuel economy. It's a good article that is definitely worth taking a few minutes to read. Lately I've been making a concerted effort to apply certain hypermiling strategies as often as I can. It's not always feasible, but the techniques do make a difference.

The two biggest changes I've coerced myself into making is avoiding heavy use of the gas pedal, and eliminating idling as much as I can. Accelerating modestly isn't nearly as fun, but driving like your grandmother is in the passenger seat saves a ton of gas! (I'll admit, this is still the hardest change to adopt... I just love really driving.) As for avoiding idling, I don't turn my car off for every stop-light, but the lights that I know are particularly long... lights I wait at nearly every day of the week... for those I definitely cut the ignition. The traffic light to leave my office can be well over 3 minutes. Drive-thrus are another trap to be avoided like the plague. That is much too much time spent with the engine running while not making any forward progress. Nine times out of ten, when I go inside there's barely any line-up there... yet I can't say the same about the drive-thru window.

The other tips mentioned in the article linked above all help too.

I've personally seen a difference of as much as over 18% between the mileage of a tank of gas driven how I usually drive, and a tank of gas hypermiled as much as possible. Even a "moderate" amount of hypermiling saves me over 12% per tank. Over a year that's nearly 10 tanks of gas for me.

Ten tanks of gas at well over $70 per fill-up (@ $1.499/L - current price) is over $700 that I would much rather see in my pocket than the oil company's.