I've been reading an article on cars and their CW values and what it
means for efficiency. The article is in German but I thought the figures
given for the MX-5 may be interesting so here it goes.
Top down: 0.45 cw
Soft top up: 0.39 cw
Hard top up: 0.37 cw
At 150 KMPH The Hard top uses 0.3 litres of gas less than the soft top
per 100 KM. With the top down 1.4 litre extra gas is used per 100 KM
(also at 150 KMPH). This can of course also be translated to possible
top speeds but the article does not do that - it only comments that no
one drives top down at more than 150 KMPH (Sort of making me "no one" as
I do - it's loud but otherwise fine).
http://www.autobild.de/artikel/autos-im-windkanal_666465.html
http://www.autobild.de/mmg/mm_bildergalerie_668619.html?tab=0&page=15&bid=0&m=&e=&i=
http://www.autobild.de/mmg/mm_bildergalerie_668619.html?tab=0&page=16&bid=0&m=&e=&i=
http://www.autobild.de/mmg/mm_bildergalerie_668619.html?tab=0&page=17&bid=0&m=&e=&i=
No real surprise that the soft top is a little less smooth or that top
down is even worse when it comes to smooth airflow.
Here are some other figures (also from the article):
The ten most efficient
1. BMW 5er 0,26
1. Mercedes S-Klasse 0,26
1. Lexus LS 460 0,26
1. Toyota Prius 0,26
2. Audi A4 0,27
2. BMW 3er 0,27
2. Mercedes E-Klasse 0,27
2. Mercedes C-Klasse 0,27
2. Mercedes CL 0,27
2. ****sche 911 0,27
And the ten less efficient
1. F1 Race car 1,2
2. 2 Mercedes Actros 0,81
3. 3 Morgan Roadster 0,6
4. 4 Land Rover Defender 0,59
5. 5 Hummer H2 0,53
6. 6 Mercedes G-Modell 0,52
7. 7 Morgan Aero 8 0,51
8. 8 Jeep Wrangler 0,49
9. 9 Jeep Commander 0,41
10. 10 Chrysler PT Cruiser 0,38
Kind regards
Bruno
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