Effective speed
The speed a vehicle can actually hold on a given ground type, rather than the cap printed on its specification sheet.
Also known as real speed, achievable speed.
Top speed is a limit the engine may never reach. Effective speed is what the engine, the weight and the ground resistance produce together, computed per terrain type, and it is usually well below the quoted figure on anything soft.
It is the number that explains why a vehicle rated at 55 kilometres per hour crawls across a field while another rated at 45 crosses it comfortably.
Related terms
Top speedThe highest speed a vehicle is allowed to reach, which it only attains with enough engine power and forgiving ground.Terrain resistanceHow much each ground type slows a vehicle down, quoted for hard, medium and soft terrain, where lower is better.Power-to-weightEngine horsepower divided by the vehicle's weight in tonnes, the single best predictor of acceleration.AccelerationHow quickly a vehicle reaches speed from a standstill, which matters far more in practice than its top speed.