Interesting question Heinz .... I've had cause to use rolling roads a fair bit but you can overthink it ... I use the same dyno with the same operator (Damien at Daytuner in Ripley for my racer 🙂)... absolute accuracy against some benchmark? ... whether there's a tiny difference in drag between one gear in a box or the next? .... I've just been interested in the comparison between what I had and what I've got after a remap after some 'improvement' I've made .... just a comparison to see if what I did put more power to the road or less ... the graphs are also useful for deciding optimum shift points and setting shift lights (and where to set your rev limiter to not lose anyrhing useful).

I've never needed to look that closely at absolutes ... if, as you say, they just lump the drag of the dyno in with the drag of the car parts then that would go a long way to explaining the variation between different power runs on different dynos (though I assumed there would be some process for identifying the drag of a particular dyno over a period of time and factoring that out of the final graph??) ... glad I'm only interested in comparative figures from one given dyno/operator ... I suspect there's a big can of technical worms waiting to cloud the issue if it's absolutes we seek 🙂

K

Ps ... and that's before we get into the understandable Human desire for a shop who fits go faster goodies to give the punter a graph that makes them happy 🙂