just back from dyno......

[stamford]

Something does not add up there then

[Leasky]

maybe a rubbish dyno

[al_roverMG]

See this is why at the wheels figures are nonsensical at best and a damm right lie at worst. The figure for the flywheel value will vary very little from one set of rollers to the next. The figure for the "at the wheels" (which is a nonsense in itself because it is actually the torque value measured at the rollers then calculated for the power figure at the flywheel and then the losses re-removed to give power at the rollers) will vary dependant on how long ago it was calibrated.

When a rolling road is calibrated the in built losses (ie the losses due to friction, inertia of the rollers etc) is taken into account but over time these change and so the "at the wheels" figure will have inaccuracies.

I spent a long time looking into this (call me sad or just curious to find out how things work) after 2 rolling road days at different places on following weekends with my CTR. Both gave me 238bhp at the flywheel but there was something in the order of 30bhp between the "a the wheels figures" and the second dyno was a brand new chassis dynamics setup which had been installed the weekend before while the other was an old sun rolling road which had been in since Jesus was a little boy. That is why i go into rant mode every time some spouts about "at the wheels" figures.

[RalphG]

The thing is though that rollers only measure the 'at the wheel' figure. They then use a formula to calculate the flywheel value. The better rolling roads calculate the transmission loss for the vehicle by unloading the engine and letting the rollers slow naturally and therefore find the resistance. Other rolling roads use a pre-calculated loss averaged for a sample set of cars of the type.

The only way to get a true flywheel value is to take the engine out of the car and connect it to a dyno. Rolling roads are not dynos.