Firstly, the ratios are carefully calculated to allow the driver maximum scope for maintaining appropriate road speeds without straying outside the most economical rev range. Ratios for the lower gears are more widely spaced than those of the higher gears, enabling brisk acceleration with a minimum of shifts. The narrow steps at the top end make it easy to select a gear that keeps the revs close to the optimum, regardless of speed or road conditions.

Secondly, fuel consumption is improved by a slick, smooth, positive gearchange. Every time a gearchange takes place, a small amount of fuel is wasted. The faster the change is completed, the lower the losses.

Thirdly, fuel is saved by minimising transmission losses caused by needless friction. Inevitably, there will be some friction, especially where gear teeth are engaged to transfer motion from one shaft to another. The design of the gear teeth, allowing for just the right amount of momentary contact as the teeth engage, is a critical factor in minimising friction losses.

Fourthly… also of importance in reducing friction are the lubricating and cooling effects of oil. Too little oil will cause overheating and premature mechanical wear or failure. Too much oil tends to act as a braking force on all the rotating shafts and gears. This in turn reduces the amount of torque transmitted to the driving wheels; extra fuel is needed to maintain road performance. A Scania gearbox has a lubrication system that circulates precisely the right amount of oil at all times.