Half the range

The bike on the roof costs one or two liters more fuel, as experienced drivers know. But how does the additional consumption behave in e-cars? The ADAC did the test.

More drag

A trailer or a transport body increase consumption, logically. More weight and higher drag require more energy. However, energy is a precious commodity, especially for purely electric cars. Because the range is shorter than with combustion engines and the charging process takes longer than filling up with fuel.

The German motorists’ club took a Kia EV6 and ran through various scenarios: both with bodies and with trailers.

At 120 km/h, the testers raced down the autobahn with a roof rack and no bicycles. The additional energy consumption was comparatively low at five percent (see graphic). However, if two bikes are strapped in, consumption increases by a whopping 33 percent. And thus achieved the same result as a roof tent. The sensible alternative is a bike rack mounted on the trailer hitch at the rear. There, the testers measured an acceptable additional consumption of eight percent.

Extreme additional consumption

If the driver hooks a trailer, the energy consumption increases drastically. An unloaded single-axle trailer is of course hardly noticeable, consumption increases by one percent. However, if a body is mounted, 24 percent add up to the standard consumption. A horse trailer recorded an increase of 83 percent, a caravan even 103 percent. The latter thus halves the range.

Saving at low speeds

While the weight is noticeable on inclines and when accelerating, the air resistance is decisive at higher speeds. The following formula applies: the air resistance increases with the square of the speed. The ADAC provides an example from practice to clarify this. At 80 km/h the additional consumption with a trailer hitch was 54 percent, at 90 km/h it was 79 percent and at 100 km/h it was 103 percent. This proves that when traveling with the caravan, the range can be positively influenced by gentle speed. Swimming along with truck traffic is an efficient driving style.

How much influence does weight have on fuel consumption? Here, too, the ADAC technicians tested various scenarios. Empty, with low weight, higher payload and maximum load: The testers accelerated from a standstill to 100 km/h and then braked to a standstill.

Weight: little impact

The result is astounding: additional loads show a rather small influence on consumption. The difference between unloaded (driver only) and fully loaded (plus 280 kilograms) was a total of just six percent.