Improving the Aero on my road car

[fussell]

Hi All

I have an idea of improving the aerodynamic efficiency of my Smart Roadster. It has fake intakes either side, but on the passenger-side it is half open, with ducting behind directing an airflow to the airfilter. While the driver side is completely fake, and blanked off.

I was wondering if I opened up these intakes and directed the airflow thru/over/under the engine bay, via sealed ducting. Then out the fake outlets at the rear. Would this improve aero or not?

[Bazza]

The first problem is owning a Smart roadster; improving it's aero efficiency is really the least of your concerns.

Though if for some strange reason you want to improve it, there's a lot of ways you could go.

The ducting probably wouldn't do a whole lot. The intake is tall and thin, probably right in the wake of the front wheel and once routed through and around and in and out of the engine bay the airflow would be next to useless. It MIGHT help relieve the step from the blanked off intake by bleeding pressure into the engine bay (if it even goes that way at all). I can't tall from the pictures, but if the blanking isn't that recessed into the duct and you open it up, then air could end up coming out of the engine bay and backwards through the duct (high-speed, low-pressure air outside the car relative to whatever's in the engine bay).

If you wanted to improve it, some rim blanking would be a good start. A simple front splitter and underbody panels would probably work wonders (don't quote me on it though, I haven't seen the underside of a Smart). That wing seems dubious at best, too.

[richard_leeds]

Surely the best aero improvement would be to get rid of the inlet by replacing it with more streamlined bodywork? OK, that might be more radical than you intended, but this could open up some interesting hypothetical discussions.

Have you seen this Mitsubishi study about vortex generators on road cars? Simple and evidence based.
viewtopic.php?f=3&t=6250
http://www.mitsubishi-motors.com/corpor ... 16E_03.pdf

Also:
viewtopic.php?p=197685#p197685

As an aside, it's really annoying how stylists add fake aero features such as fake intakes, spoilers or those exaggerated diffusers on Ford ST variants.

[Jersey Tom]

"Improved" aero is awfully vague and doesn't really say what you're trying to accomplish.

Is less drag what you're after? Or what?

[fussell]

Jersey Tom, Ye I mean 'less drag'.

Bazza The fake intake is only set back about 10mm.

My idea was that the fake intake creates a blockage, and to eliminate this I thought of opening it up and then spilling the airflow out of the back, into the vacuum behind the car.

[marcush.]

I will have to dig a bit for it ,but panel adjustment and gaps is also a very worthwhile area to improve aero !
Hopefully i can retrieve the relevant example pictures...

for starters:
http://www.ltas-aea.ulg.ac.be/cms/uploads/VehicleAerodynamics02.pdf

[machin]

What do you hope to gain from reducing the drag?

At 70mph your car will be absorbing something in the region of 20bhp in aero drag.... if you cut that by 10% (which I would consider to be a lot), it will only "free up" 2bhp for acceleration... at 35mph it'll free up less than 1bhp.... If you only use your car on the road (as opposed to in some sort of competition were every 0.001secs can make the difference between places) and you want to make the car feel quicker then I would put effort into other mods (power and weight).

I love the Smart roadster by the way; light weight, low emissions and above all: fun! good choice!

[marcush.]

Lower the car mount skinny tyres chop off the roof and you will reduce drag

But think again ,the smart has a lot of tailored blanks sheet metal -you will have a hard time cutting through the sheetmetal...

Seriously ..the front does not look prettty nor is it very clean ..In formula 1 they say good aero starts at the front..maybe a good starting point for that one ?

maybe some good source to find drag sources ..even if that is for planes...
http://www.aerodrag.com/

[Cam]

I will have to dig a bit for it ,but panel adjustment and gaps is also a very worthwhile area to improve aero !
Hopefully i can retrieve the relevant example pictures...

for starters:
http://www.ltas-aea.ulg.ac.be/cms/uploads/VehicleAerodynamics02.pdf

+1 Perfect starter that simply demonstrates the point. Nice work. Nice read too.

[mep]

You probably gain more by just increasing tire pressure to reduce rolling resistance
If you guide the air with custom made sealed ducting it might do something. The manufacturer probably didn't want to do that for cost reasons. I guess just opening the holes will increase drag otherwise they would be open already. The Coupe btw. has lower drag.
However if you want to improve general performance think about lowering ride height and things like that. I have seen once a forum where somebody had a Smart and wanted to fit a more powerful engine to it. Actually I think it is possible to generate a really good race car on the basic principle of the car as Brabus did.

[marcush.]

you might be able to retrieve the biengined development hack (6cylinder engine !) somewhere in the net...seriously..the key is weight with this..maybe someone has a set of elise MK1 brakediscs and pads to reduce unsprung weight...
The smart cars are incredibly fat .A long saturday spent to find unnecessary parts should yield a good 5 to 10 kgs ...or more.
Does a little roadster need to weigh 800kg? A Mini of the old days can be stripped with minor effort to 620kg and this with 4 cylinder full greycast iron block and head....

[fussell]

Hi All,

Some really good links posted. It was just a 'day dreaming' idea I had to reduce drag and improved fuel consumption, with the added bonus of a small performance increase. My car is lowered, but I do just drive it on the roads - too slow for a track

Since reading the posts I realise that this idea doesn't have huge benefits, but benefits never the less, and that there are other areas that I can improve. Maybe a complete rebody of the car - I'll save my pennys and get sketching

[andylaurence]

I used to have a Roadster and spent some time reducing drag to improve fuel economy. The biggest gain I got was from fitting Michelin Energy tyres on the standard 15" wheels, rather than the sportspack 3 spoke wide wheels. A grille block at the front is worthwhile - I never had a cooling problem with it whether in traffic or on the track. The car has a flat undertray from the front of the car to the engine bay. Extend it to the rear bumper and you'll see a benefit. I didn't see a measureable benefit from removing wing mirrors, so it's probably not worth bothering there. Unfortunately, it's not practical to convert the Roadster into a Coupe as that gets a noticable decrease in drag and increase in boot space! There's not much scope for weight reduction in the car, which is surprising, but the seats are the biggest way to reduce weight by replacing them with a pair of fixed back bucket seats. If you want a performance increase, then a replacement TIK and a remap will take a standard 80bhp Roadster up to >110bhp. All of the above will see change from £500 and the car will be much lighter, more economical and much faster.

Post your progress!

[marcush.]

´sure there is a loz weight to be found...it may not beobvious but belive me all you need is a decent set of scales and patience.
On my mini projects I had 10kg removed just through selecting parts by first weighing them ..some bits had an encridible spread in terms of weight - the rubber donuts a very notable example with 4oo gr tolerance for example.,also the cast suspension legs and engines as well as gearbox castings.

[andylaurence]

Yes, I've had a Mini too. Parts didn't get quite the same quality control back then as they do now. Of course, I'm sure if you're building from the ground up and have a box full of parts to choose from, then you can lose a few kg, but there are not enough Roadsters about to have a stock of parts to compare. I'd say that's pretty low down the list of things to do.

There's weight to be lost in the Roadster, just not as much as you'd expect. Some components are just plain heavy, like the roof bars. When I looked at what I could reduce weight on, there were no big gains to be had other than the seats as everything was already remarkably light. Of course, if you're building a track car, you can pull out lots of things you don't need, like aircon and if you're willing to machine new aluminium uprights, you could save a few kilos there too. Small gains though.