The two principal categories of 2WD dynamometers are single-roll (large-roll) and twin-roll. The 48" single-roll machine shown below was originally designed by Real Time, and is now available through AVL North America, Inc. It is the original "motor-in-the-middle" design in which the two rolls are suspended on the extended shaft of the central AC motor. This produces a compact design that fits into a relatively small pit.
Our most popular 2WD dynamometers are probably the Electric 8.65c and Electric 20n series. These are robust machines designed originally for the IM-240 emission testing market. They have electric inertia simulation that allows testing of vehicles between 2,000 and 5,500 lbs.
The machine shown below was installed above-ground, and includes a special ramp. The vehicle drives either forward or backward up the ramp until the drive wheels settle into the rollers. The vehicle brakes are applied, and the ramp is then raised to the horizontal by means of an air-actuated lift. This system had the advantage that no pit excavation was required. The machine can be disassembled and moved to another location with minimal modifications to the buildings.