Relationship between fuel consumption and roof

I have not notice very much difference between the two, but I do thend to drive more with the top down, no point in having it up...

Steve
 
I've not actually ever tested it, but I assume fuel consumption will increase with the roof down - increased drag. Having the roof up will make the car more aerodynamic. No idea what sort of increase in consumption there will be be honestly I couldn't care as it won't affect what I do with the roof!
 
There is a significant decrease in drag when the roof is up and a furhter decrease if that is replaced by the hardtop. drag with top up is 0.35 and travelling drag .669

I doubt it translates into more than 1mpg, but woudl of course be speed dependant

In their technical literature they focus more on lift when the roof is up/down and the effect of hardtop.
rear axle top up .12
rear axle - top down <.4
rear axle hardtop .10

Bottom line is aside the weigt increase the car is more aerodynamic and stable with top up and even more so hardtop on.
 
cj10jeeper you know way way too much about zeds :P


i was simply going to say more drag = more fuel :oops: and thats the best i could come up with :P
 
Rudd said:
cj10jeeper you know way way too much about zeds :P
i was simply going to say more drag = more fuel :oops: and thats the best i could come up with :P
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x2 ..... signs of a misspent youth perhaps! :rofl:
 
More geeky stuff, but I remember reading that lowering the roof upsets the weight distribution of the Z4 - obviously there's more weight being transferred further back on the car. Whether that's good or bad I'm unsure...

Also, having a hardtop fitted to the roadster raises the centre of gravity which again has an ill-effect on handling. Something to think about.

Of course, are any of us good enough drivers to notice any of these differences?!
 
Putting the roof down will increase the fuel consumption as you are listening to the exhaust more, and therefore raising the revs :)

Well, that is my scientific angle on it ...
 
No doubt in the real world a hardtop will decrease performance on twisty stuff due to extra weight more than outweighing (no pun intended) the minor aerodynamic benefit, although I believe top speed would be higher with it on due to improved aerodynamics.

Not sure about shifting the weight rearwards other than stuffing 10lbs of plastic and canvas back 2 feet.
 
cj10jeeper said:
Not sure about shifting the weight rearwards other than stuffing 10lbs of plastic and canvas back 2 feet.
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Yep, was just me remembering incorrectly. I knew it concerned Z4's but it was evo talking about their long-term E89 with folding hard roof. They claimed it made a significant/noticeabe difference to the weight distribution having the top up or down, with more rear bias with it down.

As you say, I wonder how much the E85 fabric roof mechanism weighs. Probaby not much.
 
a11y said:
cj10jeeper said:
Not sure about shifting the weight rearwards other than stuffing 10lbs of plastic and canvas back 2 feet.
Click to expand...
Yep, was just me remembering incorrectly. I knew it concerned Z4's but it was evo talking about their long-term E89 with folding hard roof. They claimed it made a significant/noticeabe difference to the weight distribution having the top up or down, with more rear bias with it down.
Click to expand...

I wonder if that was what I could feel on the vines day drive of the 35i, when I said it felt heavy compared to the 30i I drove, hmm

30i was roof up, 35i roof down

well that and all the extra gubbins (turbos etc) under the bonnet :?
 
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