Hello from Tampere, Finland
 

I stumbled upon this site while looking for info how to make my smart Roadster more fuel efficient at highway speeds. For those who don't know about smart Roadster here's a good article about it (http://www.carpages.co.uk/smart/smar...1_07_02_04.asp) . The car in the pictures is similar to mine except for the wheels.

As you can see from the pictures the shape of the car body is far from optimal aerodynamically and I quess there's quite a bit to be done to drop the Cd value from the stock 0.40 to more acceptable level. As standard the fuel consumption rises quite dramatically at speeds over 100kph and at the 120kph, the legal top speed on motorways here which I do a lot, the fuel consumption equals that of a much bigger and heavier car. For comparition the best result I ever achieved was 3.8L/100km @90kph while closely trailing a semi truck on motorway and normally @120kph the consumption rises to nearly 7 liters per 100km which almost halves the mileage compared to my best achievement.

Where should I start? Which mods should I expect to achieve the best result at least effort and cost? Vortex generators, side skirts, front spoliler??

Welcome to the site! Do you already have fuel economy instrumentation?

I think the smart is pretty well equipped for that. The onboard computer displays fuel consumption with precision of 0.1 liter and the distance travelled with precision of 1 km. If that's not accurate enough I can measure the distance using GPS and I can also monitor many engine parameters like calculated load, trottle position etc with laptop computer pc connected to the OBD socket using Elmscan5 wireless bluetooht scantool. If there's an actual difference I think I'm able to spot it.:)

Welcome to the community!

Welcome to the website. :) That's a pretty nice looking ride.

Slightly OT, someone needs to add a forum feature that displays these ratings in mpg or L/100km based on the user preference. You could put the number in a tag like .

Cd of .40? thats quite a bit for such a small vehicle.

0.4 x small area = low drag

it looks good don't it

Yea, I know that, but most cars that small are usually decent at aero. It doesn't look all that bad either.

You have a smart Roadster?!? *jaw drops*

Welcome :)

The reason why I've become concerned about this lately is that I do quite a lot of motorway driving, something like 15000 miles per year at 120kph (75mph) and at that speed I think even a little drop in the Cd would mean some real savings especially when the gasoline is so heavily taxed and expensive round here. A liter cost around 1.45 euros and converted to US dollars that's about $8 per gallon. In other words 15000 motorway miles per year at 35mpg cost me about $3500 in gas so there's quite a bit to be gained if I manage to make this ride even a bit more aerodynamic.