Speed versus fuel economy

Speed versus fuel economy

How much does your speed affect your fuel economy?

Hammer it, and you'll kill your fuel economy. But there's more to the story than than. Ford SVT Lightning shown burning it up.

We all seem to be in a rush these days. Life's time demands seem to only increase, with the delicate balance of work, family, and recreation pressuring us to maximize every minute. As a result, there is real temptation to edge beyond the speed limit to shave seconds off each mile.

But while driving fast may get you there sooner, there are some real downsides, such as diminished safety for yourself and fellow motorists; risk of a speeding ticket; and decreased fuel economy.

To quantify the impact a heavy right foot can have on your wallet, Consumer Reports recently conducted a seven-vehicle test comparing the fuel economy of each at speeds of 55, 65 and 75 mph (about 88, 105 and 120 km/h). The results show the faster you drive, the more fuel you burn - no surprise there. However, the most significant change in fuel economy comes from the most fuel-efficient vehicles tested.

The Honda Insight hybrid showed the largest drop in fuel economy - over 15 mpg (18.8 L/100 km) going from 55 to 75 mph. The Toyota Camry returned 40.3 mpg (7.0 L/100 km) at 55 mph, but that reduces to almost 35 mpg (8.l L/100 km) when the speed moves up to 65 mph and drops to almost 30 mpg (9.4 L/100 km) when speeds reach 75 mph.

That's a drop of about 5 mpg for every 10 miles over 55. Vehicles with lower fuel efficiency had the smallest drop. The V8-powered Mercury Mountaineer (not available in Canada) has a fuel economy of 23.8 mpg (11.9 L/100 km) at 55 mph and that drops to 21.2 mpg (13.3 L/100 km) at 65 and 17.8 mpg (15.9 L/100 km) at 75 mph. See the chart below for more details on all the vehicles tested.

In this economy, saving money is important. But it's not that simple. As the adage goes, time is money and it can sometimes be worth spending more to get somewhere faster.

Another consideration is traffic. There is debate as to whether driving slightly over the speed limit is more dangerous than going slower. Some say it is the difference in speed of vehicles that contributes to accidents - not speeding - and that it's best to move with the flow traffic.

Make & model	55 mph	65 mph	75 mph
Acura TSX 2.4-liter 4-cyl.	39.9 mpg	35.5 mpg	30.7 mpg
Honda Insight 1.3-liter 4-cyl.	51.9	44.8	36.5
Lexus RX350 3.5-liter V6	30.9	27.4	23.0
Mercury Mountaineer 4.6-liter V8	23.8	21.2	17.8
Toyota Camry 2.5-liter 4-cyl.	40.3	34.9	29.8
Toyota RAV4 2.5 liter 4-cyl.	34.6	29.3	25.9
Toyota Yaris 1.5-liter 4-cyl.	42.5	37.9	34.0

Source for chart: Consumer Reports

CarTest.ca. Posted Nov. 4, 2009

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