How do you calibrate a rolling road?

[wazza]

I was asked this at work the other week.
One of the guys suggested that you get a horse to stand on the rollers and get it up to a gallop

[johneroberts]

still sounds funny paul
but how do they calibrate it?
cheers
jr

[simple1]

And I thought Thursday was April Fools day

[Ryan_s3]

Load cell types use a known weight on a known lever arm length to apply
a known torque to the arm that depresses the load cell itself. The load
arm is then either adjusted in length or the cells electronics tweaked
to calibrate. If you are a lateral thinker, then yes, this means results
are easily fiddled .
answer from my tuner;
You have 2 different types of chassis dynos:
1) Load Cell dynos
2) Inertia dynos
The latter are not normally as accurate as load-cell dynos.
You use a load hung from a long arm, at 90 degrees, and
this will apply a set load/torque to the rollers. Ideally, we want to
put 10 lb/ft of torque into the roller. So, if we use an arm that is
3.33ft in length, and hang a 3lb weight from it, we have 10lb/ft of
torque generated. The output of the load cell is then measured to
ensure that the electronics are perfectly calibrated to the
mechanical side of things.
Now, the dyno software will have 2 main inputs to measure everything
we need for power:
1) Load (as measured by the load cell)
2) Roller speed (equivalent to our engine speed)

By knowing these 2 values, the dyno can then work out power from the
torque measured, etc, etc, etc.

There are MANY variables that can be changed on such dynos to give
different readings, and in the UK a great number of rolling road
centres give "optimistic" figures, as this is generally what the
public want to see, but then it causes issues when you take the same
car to a more "pessimistic" dyno and wonder where the power went.

bit of a chopped down reply because it was rather long..regards Ryan

[simple1]

I prefer the first version, although the second is probably far more accurate

[Louis]

I was asked this at work the other week.
One of the guys suggested that you get a horse to stand on the rollers and get it up to a gallop

Then you "must" Check Linearity at "walk, trott and canter.

[simple1]

[ Linearity .

To me that would imply tracking.........can you get four hoof alignment????????????

[Louis]

Neigh. All that horse power could lead to quite heavy Emissions though
Who has the most accurate dyno? Just out of interest.