2012 Nissan Leaf with roof rack fittedEnlarge Photo
We’ve passed spring break, the weather is getting warmer and you’ve turned your weekend attentions to camping trips, DIY projects and outdoor sports.
For many Americans, that means digging roof racks out of their winter storage and securing them on top of the family car for the season.
If that car is electric however, you’ll want to think twice: It could severely reduce your car's range.
That’s because fitting roof racks to almost any car increases both the frontal area of the car and its drag coefficient.
In short, a roof rack changes the shape of the car it is fitted to, making it less aerodynamic and increasing the amount of energy needed to push it along.
Even with an empty roof rack fitted, gas car fuel efficiency can be reduced as much as 12 percent. Carrying something like a bicycle could reduce gas-mileage by 30 percent.
In a gasoline car capable of 300-500 miles per tank, a reduction in fuel economy of between 10 and 30 percent will require you visit the gas station more often, hurting your wallet more than anything else. Unless you're going into the wilderness, you'll still reach your destination.
In an electric car with a range of only 80 miles or so per charge however, a 30 percent reduction in efficiency means finding somewhere to recharge every 50-60 miles. That could seriously affect your trip planning.
We experienced the dramatic effect roof bars have on electric cars first-hand recently, thanks to a weekend trip to buy a new shelving unit.
Driving to the store in a 2011 Nissan Leaf with Thule roof rack fitted, we noticed the roof rack’s dramatic effect on the car’s range after a few minutes on the freeway.
Instead of predicting a range of between 50 and 60 miles for a three-quarter full charge, our car predicted nearer to 35.
We arrived at the store after 10 miles, with the Leaf using around a quarter of its charge to drive that short distance.
2012 Nissan Leaf (RHD)Enlarge Photo
After fitting the 95 pound shelving unit to the Leaf, the 10-mile trip home burned through almost all of the remaining charge.
Interestingly, neither handling nor performance seemed that badly affected by our load, with our test car happy to match other cars on the freeway in terms of acceleration and speed.
However, range did suffer, arriving home with enough charge for an estimated 5 more miles of travel.
That day, since unplugging our Leaf with a 100 percent charge that morning, we’d covered just 43 miles. As a reminder, 23 of those miles had been covered without any roof rack fitted, using up just a quarter of the available charge.
Admittedly, our experience combined poor weather, freeway driving and a car laden with two adults, two children and a 95-pound load -- but it illustrates how dramatically load can affect range.
If you’re planning on fitting a roof rack to your electric car, remember that weight, and size of your load will affect how far you can travel on a single charge.
If you’re going longer distances, remember to plan extra recharging stops to account for the loss in range from your heavy load.
Oh, and don't leave roof racks on your car when you don't need them.