[JulianEdgar]

I think the paper is a good find, and I have added it to my 'second edition' file for my book. Basically, I think any published data like this is worth assimilating.

But as (I think) Aerohead said: beware models, especially those without wheels.

And then, as Aerohead didn't say, beware entities with wheels not tested in wind tunnels with rotating wheels.

And then as I say, beware any models versus on-road testing.

Hmmm.

I glanced through the 'real car' stuff in the paper but it will take a fair bit to dig out the essential points.

However, based on the research I did for my book, and on the measurements I have made on the road, I think that all 'rules of thumb' like those in the paper need to be treated with great skepticism.

Basically, so much depends on what is happening ahead of the diffuser. Rear wheel wakes? Even front wheel wakes? Surface discontinuities leading to thicker boundary layers?

Even, as I was reading today, it also depends on the wake strength, because a stronger wake (ie lower pressure) creates better flow attachment on a diffuser.

So much better to simply measure real pressures under your real car on a real road.

(And I don't have any questions for the author at this stage.)