How to read a Hub Dyno?

[djvoodoo]

Tried searching, but didn't find much.....

How do you read a hub dyno vs a roller dyno, specifically rpm vs power vs boost.

Im accustomed to a roller dyno where i can either see road speed and power or rpm vs power/ boost etc, but hubs read very differently? Example attached.

How do you covert this to a more traditional figure?

[GTSBoy]

The speed reading is axle speed. That is equal to engine speed multiplied by the gearbox ratio (which really should be 1) and the diff ratio.

It's not hard. Unless you don't know the diff ratio. If you don't know the diff ratio, you have to guess and take the hit on the possible error. Most R chassis are going to be 4.11:1. Autos either 4.08 or 4.36.

[Kinkstaah]

Yep usually a decent dyno operator will key in the diff ratio of the car on the dyno, the screenshot you've used.... doesn't... for reasons unknown. 1600 would/should be 6576rpm if that car had a diff ratio of 4.11.

Reading the output of either dyno should be very similar once that's taken into account.

[KiwiRS4T]

The only really useful numbers on a dyno readout are the before and after numbers for your car.  Brands of dynos differ as well as the difference between roller and hub dynos (with the latter not having the problems of tyres slipping)  but also operators can usually choose a wide range of settings which makes it difficult to compare performance between cars on different dynos. Some more annoying  settings are using km/hr instead of rpm   and some use an estimated flywheel power  number.

[GTSBoy]

16 minutes ago, KiwiRS4T said:

Some more annoying  settings are using km/hr

To be fair though, on a roller dyno that's more informative than the native roller rpm number and it at least intrinsic to the measuring device.