Calculating flywheel BHP from Wheel BHP

[Brad Tipp]

How do you convert a rolling road "at the wheels" BHP figure to an at the flywheel one?

 

 

[Simos]

You measure the power lost in driving the wheels i.e. loss in gearbox, propshaft, diff, tyre deflection, tread friction etc etc.

 

The way "some" rolling roads do it is measure the time for the wheels to slowdown from when the power reading was taken. The faster they slowdown, the more power is lost. From this you can have an educated guess as to what the flywheel was generating to give a given at-wheels figure with a coast down time of X.

 

If you want a complete guesstimate then Sevens from the various postings using fairly standard kit (no straight cut gearboxes etc) seem to lose in the region of 30-40hp in the transmission/wheels etc. But as I say that is a complete fudge figure based on lots of replies...

 

Cheers, Simon.

[Roger King]

As simon says (hey we can make this into a game!), it can only be an educated guess based on perceived transmission losses measured.

 

In reality these losses can only be approximated and in any case are different on flat tarmac to round rollers.

 

So take the figures as a guide only.

 

Incidentally, I recently saw a rolling road power sheet that had calculated flywheel power to 1 decimal place of a horsepower. All I can say is, that if the operator genuinely believes this to be a realistic picture, you are probably better off going to someone who uses their brain.