Originally Posted by euromodder
Nobody on here has been able to proof they do improve FE, and it wasn't for lack of trying
I still think they could work, but not in the usual massively/truck-sized variety on a regular car.
Something more subtle might do the trick. Renault / Dacia had them on the rear roof line of their eco-Logan.
OK, but Dacia probably had some wind-tunnel time via Renault to try things out ?
We know there is a return with some people from a grill block (although both you and I have tried these and not seen a significant difference - but that might be the difference in Euro vs US driving conditions - long cruises and journeys in the US vs. our more busy and choked roads).
We have seen coast downs with boat tails which seems to suggest an improvement and with wheel covers (front and rear), new noses, wheel spats, mud flaps removal or reversal. Even some differences with mirrors folded and removed vs not.
The coast downs with tabs suggest minimal effect and threads testing them on cars longer term show no difference at all as far as I can tell, or whatever difference is recorded could well be inside an error range.
So at the moment we have to say at best "maybe" or it has "potential", but on a firm this-makes-a-firm-difference basis we have to say "no".
@Neil - I would love to see those instructions and for someone to do some proper testing having followed them.