Metro undertray / belly pan

[majestic]

Anybody know more info on this audi? Specifically im looking at the very small panels located behind the front tires rated at a decrease of 4 counts of drag for each side!

Theres got to be more to those than what the pic suggests.

[Cd]

Originally Posted by majestic

Anybody know more info on this audi? Specifically im looking at the very small panels located behind the front tires rated at a decrease of 4 counts of drag for each side!

Theres got to be more to those than what the pic suggests.

I know this sounds like a lame idea, but I'll post anyways - I will sometimes go by car dealerships and act interested in a certain car, with the real intention of just seeing the underside.
If you can find a used A4, just act like you want to see if it has any leaks and climb under there.
Post pictures if you take 'em !

[MetroMPG]

Originally Posted by Tango Charlie

Darin, did you ever reinstall your belly pan? Swap out springs?
What are your current thoughts/conclusions?

Whoops - super delayed response.

No, I never did either. But both of those are still on my to-do list. (Which never seems to get done...)

[Christ]

Originally Posted by Cd

I know this sounds like a lame idea, but I'll post anyways - I will sometimes go by car dealerships and act interested in a certain car, with the real intention of just seeing the underside.
If you can find a used A4, just act like you want to see if it has any leaks and climb under there.
Post pictures if you take 'em !

If you're good, you can get them to put it on a lift. Don't ask on a busy day, though. Just tell them that you want to get a good idea of what under-car maintenance will involve.

[Synchronicity]

Why not just tell them the real reason you want to look under the car? - to check out the aerodynamics because you know it affects fuel economy.

If enough people did that, the word might get back to car manufacturers that some people car about this stuff & it could potentially influence your decision in buying a new car (well I'm sure it would if you were in the market for one).

[efirefly]

Hi. Does anyone have a template for an undertray for a 96 firefly? Thanks

[MetroMPG]

Hi. I didn't make a template for mine. But it's not that hard to just get underneath the car and figure it out.

The area that needs the most creativity is the rear suspension, since the control arms stick down into what would otherwise be relatively clean airflow. And there's not much distance to taper back "up" before you get to the end of the car. (Plus you don't want to taper up at too aggressive an angle or you cause flow separation anyway.)

[paulgato]

Nice thread. It looks like the potential gains from a full belly pan are modest, but it appeals to me as it is the only aero mod I can think of that is more or less invisible. I don't want my car to attract too much attention. (Well, removing the longitudinal roof bars is an almost invisible mod, but that probably won't make much difference to drag at all.)

[Christ]

The longitudinal bars aren't going to make enough difference to get outside static noise, but it will help unless they serve some other innocuous function to aerodynamics [there's a car that removing the outside mirrors actually makes the aero worse, etc].

On some things, you have to choose between utility and economy to some extent. If you never use the roof rack bars, remove them. If you honestly will use them at some point, leave them there. They ain't gonna hurt anything.

Belly pan is a good mod that is, as you say, basically invisible. It will also help with long-term resale value in some cases, if that's a concern to you, since not only does it protect the engine bay from underneath, but also the entire underside of the car, from dirt, rust, and corrosives.

Wheel spats are also 'basically invisible' because they install under the car behind the tires, and a modest lowering and/or a front 'lip' on the bumper also provide reasonable gains for little expense and will be 'basically invisible'. Between a modest lowering, a belly pan, wheels spats and maybe going up one size on tires [due to reduced aero load] you may see up to a 15% overall gain in fuel economy [depending on the driver and overall configuration, of course] without any/much expense and very little 'noticeablility' increase.

The reason for going up a tire size is because you're reducing aero load and your car was designed with a certain tire size both for aesthetics and to account for average load while cruising. You've altered that load, so your engine will be operating in a less efficient range of the BSFC map while cruising. Going up a tire size will increase load without increasing rolling resistance [generally speaking], and also fills the wheel well slightly better, for added aerodynamic benefit.

[paulgato]

Going up a tyre size is an intriguing idea. Of course that would put the speedometer and odometer out, but perhaps the different tyre sizes can be compensated for in the ECU options? (via VAGCOM or similar?) My tyres are all new though, including my winter set, and are all of the standard size, so I won't be making any changes there for quite a while.

I've had this car for two years and have never used the roof bars yet, and I don't own a roof rack (attaching luggage to the longitudinal roof bars without transverse roof bars is pretty difficult) so my guess is I will never use the roof bars. I didn't in my last car either and I had that three years.

I reckon it would be possible to remove the bars in a temporary and easily reversible manner by cutting neat round holes in the head lining (with a sharpened length of pipe in an electric drill?) to access the six securing bolts, and using PVC electrical insulating tape of a matching colour (black) to cover the six holes in the top of the roof. (I reckon that covering the holes with tape will make corrosion on those holes LESS likely than having the holes hidden under the roof bars, where corrosion can develop undetected.)

As you say the difference that removing the bars will make to mpg will be real but probably unmeasureable. The non-estate version of the Golf has no such bars so I doubt they contribute in any way to aerodynamics.

I'd also like to try a front air dam, as it seems that can have a surprising effect on mpg, but I am nervous that it would look too weird. That's certainly less work than a full belly pan.