IS it really as simple as A, B and C? Mercedes-Benz thinks so. Its B-class slides right into a segment above the A-class but below the C-class, thereby filling a niche that many didn’t think existed. Its 100kW and (turbocharged)142kW 2.0-litre petrol engines have been around since late last year and now Mercedes has joined the diesel putsch with an 80kW 2.0-litre turbo-diesel. But don’t let the kiloWatts fool you. The B180 CDI – don’t ask about the model designation because we're confused too – develops a meaty 250Nm from 1600rpm, just 30Nm shy of the force-fed B200 Turbo. With that type of low-down torque the B180 CDI is spirited and frugal. But while performance, economy and value (it's the same price as the entry-level B200) are strong points, the driving experience isn't as sharp as we expected.