Torque rolling road vs dyno figures

[haynes]

A power reading from a dyno is at the flywheel, and a power reading on a rolling road is measured at the wheels. More modern rollers then loosely calculate power at the flywheel based on run down. The 2 figures are different due to power loss in the transmission (ok i'm ignoring effect of different dynos on different days etc). Does anyone know if torque suffers from losses through the transmission, - torque being higher at the flywheel than the wheels? In fact isnt torque measured and power then calculated?

[timbrown]

predicting this will be the start of a MONSTER thread...
torque does get lost through the transmission ( and tyres ) between the flywheel and the tyres, but it's multiplied by gear ratios on the way ....
so 100ft-lbs at the tyres could well be 110ft-lbs at the flywheel ( adjusted for gears etc )
have a look at
www.pumaracing.co.uk/mainmenu.htm
for the best explanation I've ever seen

[Mr2Mike]

haynes said:

Does anyone know if torque suffers from losses through the transmission, - torque being higher at the flywheel than the wheels? In fact isnt torque measured and power then calculated?

Torque is the *only* component of power that is lost in the transmission. RPM cannot be "lost" in a manual transmission (an automatic with a non-locking torque converter is obviously different).

[minimax]

hang on, so rolling roads measure torque not horsepower?

[Fatboy]

Directly yes, it's the torque that is measured, and the horsepower is than calculated from the torque and rpm figures...