Volvo FM340

Beyond the series, the axle formula determines what a truck is actually suited for. The first number counts the wheels (strictly, axle ends), the second the driven ones: 4x2 means two axles with one driven, 6x4 means three axles with two driven (tandem) axles. A 4x2 is the most common and most economical configuration for long-haul work on made-up roads. A 6x2 has a trailing, often liftable, third axle and is also used in long-haul transport where higher payload matters more than a small fuel penalty, whereas a 6x4 with two driven axles gives more traction for construction work and difficult terrain. An 8x4, usually with two of its four axles driven, is typical for tippers, concrete mixers and crane trucks carrying a fixed heavy body.

The FH series naming carries a mix-up that trips up even people who work in the industry: historically, the number after 'FH' denoted engine displacement in litres — FH12 for the 12-litre engine, FH16 for the 16-litre engine, both introduced in 1993. That logic still applies to the 'FH16' designation today, even though the 16-litre engine is now offered in power ratings up to 750 hp — the '16' remains a displacement figure, not a power figure. Across the rest of the FH range, however, the naming was switched over: a designation such as 'FH 460' refers to 460 hp of output from the D13 engine, regardless of its actual displacement. Mixing up the two systems can lead to mistaking a lower-rated FH16 for weaker than an FH carrying a high three-digit number, when the opposite can be true.

When buying used, the axle formula is a key criterion because it can practically not be changed afterwards: a 6x2 with a lift axle is a poor fit for constant work on unmade construction sites, while a 6x4 used purely for long-haul burns extra fuel from the weight of the second driven axle. It is worth checking the condition and operating hours of the lift axle specifically on 6x2 trucks, since it can be overworked when a vehicle has been used outside its intended role. It also pays to cross-check the power figure on the registration document against the model designation, so as not to confuse displacement with output on an FH16.