Pace versus Space: BMW and Mercedes Hybrids

BMW ActiveHybrid 5
BMW ActiveHybrid 5
New mid-size hybrid cars from BMW and Mercedes take very different approaches to getting the best from an electric motor’s assistance

They may be arch rivals, but German prestige brands BMW and Mercedes-Benz see the world rather differently. For evidence, look no further than the pair of mid-size hybrid cars that will be offered by the two manufacturers this year.

BMW’s ActiveHybrid 5 – a hybridised version of the 5-Series saloon – is a performance-orientated car that pairs a 340bhp six-cylinder petrol engine with a 40kW (55bhp) electric motor. The result is remarkably muscular – the engine alone is the same unit that powers the 535i, which is not known for its lack of grunt. As a result, BMW’s hybrid can get to 62mph in just 5.9 seconds. Economy, meanwhile, is in the 40mpg to 44mpg range and CO2 output will vary from 149 to 163g/km, depending on the width of the car’s tyres.

Mercedes E 300 BlueTEC HYBRID
The hybrid plan at Mercedes is somewhat different, with a more obvious focus on frugality rather than outright pace. The upcoming hybridised E-Class is unlikely to be mistaken for an AMG Mercedes, even if it isn’t exactly a slug. The E300 BlueTec Hybrid can complete its sprint to 62mph in a respectable 7.5 seconds, but the benefit of this lower outright performance will be felt at the pumps, where the official figures are 62.7mpg and 109g/km of CO2 – remarkably good results for such a large car.

The excellent economy is partly due to the choice of a diesel rather than petrol engine under the bonnet. The E-Class hybrid combines a 20kW (27bhp) electric motor with a 204bhp, 2.1-litre four-cylinder turbodiesel.

While the performance and ethos of the BMW and Mercedes cars may differ, much of the engineering is similar. Both manufacturers have integrated the electric motor closely with an automatic transmission, for example – an eight-speed gearbox in BMW’s case and a seven-speed unit in the Mercedes. Closely coupling the motor and transmission allows the electric motor to propel the car with the engine switched off – although neither car will manage much in electric-car mode.

The E300 hybrid can run on electric power alone at up to 22mph and for less than a mile, while the BMW needs to call on its petrol engine beyond 37mph or the wrong side of 2.5 miles. In practice, both cars use their batteries more often as an energy buffer than a true power source, squirreling away braking energy to assist in subsequent acceleration.

BMW has sited its 675Wh lithium-ion battery between the rear wheels, in pursuit of better weight distribution for handling, while Mercedes has managed to find room for its 800Wh battery, also a lithium-ion unit, under the bonnet – supplanting the ordinary lead-acid battery. This arrangement has been to the benefit of luggage space, and indeed the hybrid Mercedes can be ordered in estate car or saloon format.

While the E300 hybrid’s boot space remains unchanged compared to plain diesel E-Series cars, the same consistency is not on the cards when it comes to price. UK costs have yet to be confirmed, but converted continental euro prices suggest a starting point around £43,000.

The BMW ActiveHybrid 5, meanwhile, costs from £45,950 – a £5,470 premium over the 535i.

For more information on the hybrid small family car, click here.

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