Vitesse a CdA of 0.360. Early Vitesses had a rear spoiler but no deep chin front spoiler, thus it is reasonable to deduce that a rear spoiler on the same bodyshell reduced CdA by 10%. This was a significant change and to understand if it might be true I relate anecdotal evidence regarding the effect of fitting a standard rear spoiler.
A good friend and member of the Rover SD1 club, Keith Hooson, owned a Series 1 3500 Manual SD1, partially converted to Series 2 with items such as Bumpers, Alloys, and other trim. On a very regular basis (once a fortnight for 6 yrs) he motored from Bedford to Leeds, a journey of 150 miles to visit an ailing parent.
A meticulous engineer, his SD1 was always in good condition, he was usually accompanied by his wife and small children and of course, an SD1 is an ideal car for such motoring. His route was all motorway or fast trunk roads and he invariably travelled off-peak so journeys were rarely interrupted by traffic problems. A family man and safe driver in every respect, he could emphatically rely on the trip computer average fuel consumption being about 28 mpg, varying only slightly if wind or road conditions occasionally modified his driving habits.
With a small amout of help from me he fitted a Vitesse rear spoiler and from that day on, and with great repeatability, the same Bedford/Leeds journey now returned a fuel consumption of about 31 mpg, fortnight after fortnight, until sadly his Dad passed away and the journeys ceased.
The unavoidable conclusion is that the rear spoiler improved fuel consumption by 11%. No other changes were made to the car and as there were no other factors involved it would be fair to assume that the CdA was reduced by a similar amount. I doubt the extra weight would be significant because the laden weight would have varied by more than the weight of the spoiler. I have every faith in the recollection of the details related to me and of the integrity of my friend.
So, from two unscientific sources, adding a rear spoiler to an SD1 appears to generate reduction in drag from an otherwise unmodified vehicle. Thus it might be reasonable to assume that not only would the top speed be increased by some lesser amount but its carbon footprint would also be reduced. Not at all bad, and it don't half look good too! Feedback here:
If you can add anything to the above, please contact me for inclusion in the feedback page.
Rover SD1 Tips 'n Tricks - #1 - Vitesse Rear Spoiler
Note. Before taking this proposition at face value please read the alternative feedback/comments on the next page. Essentially the aerodynamisists say a rear spoiler can only increase downforce and increase drag, so what ever happened regarding the story below it was not due to the rear spoiler. Various arguments are put forward to counter the anecdotal finding but they don't explain how the improvement occurred when there was no change to body shape or ride height. Either way it is a thought provoking subject for various Rover SD1 Forums.
Now here is a tip you can't ignore. Do you fancy a go-faster accessory that also improves your fuel economy? Well, if you don't already have a Vitesse rear spoiler fitted to your car then you might want to consider the following.
First of all, its not a speed thing! It's to do with reducing drag and if that can be achieved then it stands to reason that such a result will translate into better economy and more speed.
So whats going on? Basically it's about a feature known as the Coefficient of Aerodynamic Drag or CdA. Karen Pender's book indicated that an '82 3500SE SD1 had a CdA of 0.405 and an early SD1