Okay you eco-freaks, the ScanGuage says I burn about 3% less fuel at highway speed with this thing on the bottom of the car:



I already have the materials to make a better version, will probably get around to it some day.

3% isn't much, but I think it's fun to prove that someone with no particular skills, with some scrap metal and a pair of tin snips, can actually improve on the design Honda probably spent millions of dollars on. Absurd, really. With the next attempt being a bit wider, and actually flat, I hope for 5%. Enough to get me to 40mpg anyway, which is a nice round number.

The gruesome details are here: http://s89686473.onlinehome.us/undertray.html

 

I was wondering when someone would finally do this. The underside of the rear end isn't exactly ideal as far as aerodynamics are concerned.

 

sweet!!!! I was thinking of fabbing up something very similar to this but using sheet metal i might just have to do it now !!!

 

Good

I was wondering if anyone ever considered modding the aeros. I always wondered why cars don't seal off the bottom lumps (heat?)

I know the tesla underneath looks 100% smooth b/c of aerodynamics as well as the fact there's nothing complicated down there in the first place, the tesla being electric.

 

nor the overall shape of the car, no?

 

It's all relative.

 

Related question. Can you tell me the source for the vortex generators you used?

 

sfenders-

if you were to lower your ride and add a verticle air dam under the lip
(or front bumper in your case) to further limit the air going under the
car, would that net any more efficiency in your experiment?

i can see how the rear bumper cover prevents air from freely
flowing under it at speed (it almost acts as a parashute) so the
lower cover you have is a good idea.

my question is how much more air can you direct away from under the
car without increasing drag on the front of the car?

 

Yeah, Airtabs. Anyone who tries those, make sure to put them on straight and at the correct spacing.

 

Probably, I guess. Everything I've read on the subject seems to indicate that lowering the car should give a bit less drag, though I've no idea by how much.

For a front air dam, there's an optimal size... a small one does some good, too big and it just slows you down.

 

ehhhh. looks janky IMO. good for you though for doing the work.

 

yah, that's wat i thought too, that a large air dam would probably
cause more bad than good.

are you going to make a wind cover for under the front too then?
even though it might be a hassle during your oil changes it might
be nice to have it. my other car has a cover i have to remove like
12 screws each time i do an oil change... its a hassle, but worth
it i suppose. keeps crap from getting stuck under the car too.

 

Nice job and great work on your data collection on your site. I think you are on the right track if you make it wider near the suspension. Once you get past the suspension spread it out up to the fenders and all the way across the rear bumper blocking off all the spaces on the underside.

I think kenchan has a good suggestion on the front air dam. Use a piece of stiff rubber possibly attached to the lip attachment points. If made out of stuff rubber it would eventually wear itself down to the proper compromise between too long and too short.

A DIY airdam installed on my last car (not a fit) worked very well increasing the fuel mileage from about 23 mpg up to 26 for the price of a strip of rubber and 1/2 hours of installation time.

 

Does anyone know where you could get a rubber piece for under the front airdam. I was thinking before of pulling off the little plastic one and putting a larger piece but i have no idea where to get one. Also what would be a good compramise on distance to the ground? I guess it would be more then likely a "guess and check method" but i figured i would ask none the less. Sorry for thread jacking but it seems like an easier fix then wrapping the whole underbody. Still a great idea but a bit more work then im willing to get into. I love the vortex generators. We use something similar on our aircrafts

 

Most cities have at least one business that supplies rubber sheeting to local factories that use conveyor belts in their manufacturing process. The sheet rubber suppliers have rubber in any imaginable formula- thick, thin, stiff, pliant, with or without fiber reinforcement cast into the rubber sheets. Stiffness is specified in "durometer". 90-120 durometer rubber would have enough pliancy/stiffness to be formable, and to hold whatever form you want, but stiff enough to keep from collapsing in the air stream and folding flat under the lip.

 

i think HomeDepot should have something you can use in their landscaping area... those black strips of rubber plastic trim you use between your lawn grass and your garden... not sure wat it's called.

 

Maybe next year I'll try that and deflectors in front of the front tires. Don't want to mess with engine cooling though...

Just working out how to do the rear undertray is enough to think about for now. Have to work out how it's going to be around the wheel arch when ice, slush, and mud are building up like they did inside the rear bumper last winter. Guess I'll just keep it simple and see what happens.

Happy to leave it to someone else to try the front air dam, I need all that ground clearance unless it's snowplow-shaped. I had one on a previous car made of fiberglass, stopped it from trying to lift the front wheels off the ground at 90mph.

 

i did this a few times with duct tape and cardboard on my dc2 when i went on road trips, it did help.
i know it cheezy, but what about holes in the bumper? just let the air out instead of deflecting it? fout or five wide oval holes? ive seen it on race cars and dragsters. just not too keen on cutting holes in my bumper to test it out. plus i havent looked upp in there lately, no idea if there is any room due to plastic and the wonderful foam bumpers are made of nowadays.

 

It kinda reminds me of a reverse spoiler. Oh yeah, uh, if this helps you anyhow, I'll try to lend you a hand with my observation as someone who frequently drives with the vent on. If you open all four windows one inch and open the vent, you won't feel anything until 35 mph. If you leave the window closed, you might not feel anything until 60-80 mph. Too bad I can't test to see how much air will travel through vent would go for with the trunk opened. Hehehe, I'm still curious wheather it will help reduce drag and increase MPG if the back window can open.

I've read your article and it makes a lot sense up to a certain point. The fit has a weight distribution of 60% front, 40% rear. You probably reduced the weight of the back using the air pushing against the car. Everytime you do that it torques force to the front. I think you've just invented the first unoticible reverse spoiler. LOL

Oh yeah, and about the filling the gas tank to consistent level part. Have you thought about filling up a backup can of gasoline to the same spot, then measure the change in angle on the fuel gauge with a protractor?

 

Many people do cut out their rear bumpers to reduce aero drag, you just have to make sure that the holes are fairly big because if they're too small the air travelling through the holes won't be able to move fast enough, which would increase back pressure, and increase drag.

If you're concerned about how to make your rear diffuser wider you could always use the Noblesse Honda Fit rear diffuser as a reference point.

And if anyone is interested or looking for a similar piece but for the front of the car Alex Motorsports and Laile/Beatrush make an aluminum panel that fits under the engine.