[JulianEdgar]

When I was writing my book, there was a disagreement between the aerodynamicist I was working with (Dick Barnard) and another aerodynamicist giving me feedback on the draft (Adrian Gaylard).

The disagreement was basically this: are car vortices created by lift/downforce (as in an aircraft wing), or are the vortices themselves responsible for the lift/downforce (and of course drag)? Dick said vortices come from lift/downforce; Adrian said on cars they were not directly related to lift/downforce. So I did a panel in the book ('Chicken or the egg?' on Page 19).

Based on what Dick told me, I've been advising people that getting the car neutral in lift/downforce will therefore result in lowest trailing vortices, and so drag.

But I've now got feedback from two more professional car aerodynamacists that I think perhaps changes that.

One aerodynamcist has said that there will be vortex development associated with both up and down forces, and that therefore a car (as opposed to a wing) with zero lift may still have strong vortex drag. Furthermore, developing low pressures under the car to counteract lift may in fact cause more vortex drag than if this were not done.

The other aerodynamcist had a bet a little both ways, as I did in my panel in the book. But he put it even more simply, saying that he doesn't think so much in vortices as in separation - and it is separation that leads to vortex development. (But then he adds that my statement in the book that 'any shape that creates lift or downforce develops drag' is definitely correct!)

Both aerodynamicists I am quoting have worked for major car companies well known for their aero excellence. One is the current head of aero of his company.

So I still am not quite sure, but I think the statement that I have made here that lowest drag will come from having no lift / no downforce should at minimum be qualified.

But there's another dimension too: on cars with lift, surely it depends on how that lift is reduced. As Dick said to me, if you place a fence across the roof, that will reduce lift - but also create lots of drag. So a smooth undertray that demonstrably reduces lift - does it also increase drag? I wouldn't have thought so - compared to having no undertray, anyway. Solar race cars aim for lowest lift/downforce for lowest drag...

Now on a personal level, I'd go for no lift (or even downforce) purely for the stability and improved driving dynamics. But anyway, reducing lift may not always reduce vortex strength and so drag, it appears.