Fly wheel power/torque versus power/torque at the wheels ?

[davetripletvr]

Hi all, can someone explain to me the difference between Fly wheel power/torque and power/torque at the wheels. What do the different figures equate to ?

[ClassiChimi]

There the same thing just taken at different points Hp at the flywheel as opposed to the actual power you feel on the road as through wheels via gearbox and dif which will be lower due to losses through the drive train.

[Super Slo Mo]

Kind of. Power at the wheels relates more or less directly to power at the flywheel, although you have to take into account the losses (usually due to friction) in the gearbox, hence why the wheel horsepower is lower than the flywheel figure. The wheel horsepower figure is the most relevant though as it's that which pushes the car down the road.

Wheel torque however is not so directly related to flywheel torque as you have to multiply it by the gear and final drive ratios.
If you knew wheel RPM for a given wheel power you could work out the torque easily enough though.

[phazed]

All we know is that "more is best........" as quoted by Stiggy.

[andy43]

I'd bet a lot of the loss is the tyre/roller interface. Rule of thumb of overall loss is 15% I think.
Those clamp-to-the-hub dynos probably give you a better "at-the-wheels" figure than roller dynos 'cos there aren't any tyres

[Super Slo Mo]

The roller is probably more representative of what's going on at the road though, since you need wheels and tyres to be able to use the car.