Hi All, Hope I am in the right place for this little question.
Does anyone have any detail on the difference in fuel economy between driving with the Hardtop up, or folded down?
I have the 2l Roadster Coupe, 2008, and spend most of my time with the roof down. Just wondering how my fuel consumption figures are being impacted by this. What kind of % loss.
(I wouldn’t want to drive a whole tank with the roof up, just to get comparative figures, would spoil driving the car).
Thanks
Regards Steve
P.S. I am getting 33.5mpg for my general driving, including my commute to work. I got 34mpg for my trip to Beaulieu on Sunday, and I wasn’t hanging around.
I once saw the comparative Cd figures for a Mk.1 with its roof up or down, though I doubt I could find it now. I recall the aero drag with the roof up was hardly state of the art even for the time, and with the roof down it was dismal (“the aerodynamics of a coffee cup” sticks in my mind).
Having said that, I’ve been keeping mpg records for years and the difference roof up vs down is so small it’s lost in the noise. I do find one or two extra mpg in the summer when the roof’s down vs winter when it’s up (could be due to warmer, thinner oils?).
Sorry to bump an old thread, but I thought I’d chuck my twopence in here. Ive had 43MPG from my car over a 60 mile run on the motorway with the roof up.
However, Im going to be driving to the south of France next week and I am intending to cruise the whole run at about 60-70MPH with the roof down, so I’m interested to hear what adverse effect this will have on economy - although I want to drive as efficiently as possible, I find that driving with the roof up amplifies road and engine noise, which over 10 hours could get quite tiring.
I’ve been keeping track of my fuel economy for years, and the only things which makes a detectable difference are summer vs winter (1 or 2 mpg worse in winter, despite the roof being up) and the school holidays which remove traffic jams from my commute. Stopping and starting is really wasteful.
With all the other confounding variables like temperature, tyre pressure and traffic I very much doubt that you’d be able to tell any difference between roof up and roof down.
Driving on French roads will improve your economy, roof up or down. They are a LOT less congested so you can get it into fifth and sit their at a constant speed for mile upon mile without the need to accelerate, change gear or brake much for other traffic.
It makes no difference that I have ever been able to measure. In summer it’s more than compensated for by the quicker warm-up, lack of headlights*, summer blend petrol and the air being a bit thinner for the car to push out of the way.
*on a Mk1, the drag of the barn doors is more of a problem than the electrical power loss; flip up the lights at 70mph and you actually have to put your foot down harder!
Not too sure about the difference hood down/hood up but I tend to drive hood down on every possible occasion. I have kept a record of every drop of petrol put into the car since bought and dividing that into the total mileage covered works out, overall, at a just over 34 mpg which I reckon is absolutely fine by me. So even if hood up all the time meant more mpg as far as I am concerned the smiles are better than the miles so down it stays!
Mine does about 36-37mpg in summer, 33-34 mpg in winter. I try to avoid short trips as much as possible (I rarely drive the 7 miles to work). On a run it can just about make it to 38mpg. It did 39mpg on its first tank with me, but that was with 5W30 oil which was only in there for a couple of hundred miles as a flush, since the car had missed a service interval; I normally use Mobil 1 0W40.
Most people seem to get in the high 20s/low 30s but I suspect they do short commutes or drive in heavy traffic. Driving the car hard doesn’t seem to make that much difference.
