DavieGravy reported that all his tires were spinnning in the same direction. My question: does this specific dyno system have four drums (or two sets of wheel rollers)?

If there are two sets of drums (total of four), I'll partially buy off on the test procedure, otherwise, something is suspect.

This is just a personal question that begs an answer. The only four drum dyno I've ever seen was in Europe and was used to determine differential dynamic braking force (i.e. front vs rear or same axle side to side braking force.) The Dutch vehicle inspectors were hell when it came to clearing an American vehicle. The primary reason: insufficient braking force, front/rear or same axle side to side. These guys loved giving you a pink slip that indicated you have a problem. The Dutch didn't seem to understand the dual brake system that was created in Europe. Who else better situated to test right front/left rear braking force!

Still wondering about a stateside four drum roller system designed to test emissions.

Mike