Complex sentence: Many wheeled off-road vehicles have four-wheel drive to keep traction on slippery surfaces; however, in vehicles designed for use both on and off road, this may be changeable so that the vehicle have fewer drive wheels when driven on the road.
Split into simpler sentences: Many wheeled off-road vehicles have four-wheel drive to keep traction on slippery surfaces. Vehicles designed for use both on and off road may be designed to be switched between two-wheel drive and four-wheel drive so that the vehicle uses fewer driven wheels when driven on the road.