What is a "chassis" Dynamometer, or "rolling road" Dynamometer?

Pretty simple really!  Its a dynamometer that can measure power while the engine is still in the chassis.  By running the wheels on a rolling road or roller, or "drum" as shown here!  Most vehicles are tested using these. Car ones are the same, but use a wider drum, or a pair of drums.  4X4 versions are also becoming more popular.

One of my Motorcycle Chassis Dynamometers fitted in Quill's race exhaust workshop development room.  It didn't stay this clean!  This one is sunk into the nice tiled floor, so that only the top 4 inches show.  Makes it easy to push bikes on and off.  The drum is 16 inches diameter so that's a big hole in the floor!

A "portable" DynoJet car "chassis dynamometer" shown below.  Don't know much about this one other than I think its towable?  But it shows graphically how the driving wheels sit on the Dyno's heavy drum's).  The same arrangement usually is sunk into the workshop floor so you can just drive on easily.

Here a picture is worth a thousand words don't you think?  OK that's Chassis dynos covered!  Oh wait, not quite...   Most of the electric EMF braked dynamometers have  a pair of small rollers close together and the tyre sits "in" the vee between the rollers.  This is bad!  Hurts power, causes tyre damage occasionally, and cars with any real power just wheel spin...  And accuracy is badly effected.

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