Aero mods - Volvo wagon
 

How about an aero treatment for the squarish back of a wagon?

I'm considering a sort of spoiler. One that continues the slight downward curve of the roof at rear of car. In cross section it would be a triangle. A lot like what's on some minivans and such, going across the rear at the roof edge. But those are usually only an inch or two, I'm thinking using a wood 4x4 so after "carving" it up I'd have 2-3 inches of lip.
Then do the same thing on the two vertical sides. Sort of a vertical fin,, continuing the inward narrowing taper of the body.

Shucks, I think I could even add a horizontal strip teardrop taper to the rear bumper - it's pretty square. If I use something crushable it should be quite safe in case of impact.

Aero people, does this sound like a good idea?

I've already done some good work on the front. Inspired by Bill in Houston's work with garden edging but I used plywood for a lowered air dam and a front undertray going back 20 inches from air dam. Next step there is to wrap the air dam around the corners towards the wheel wells.

The roof extension/taper sounds good. It will likely not be easy to detect any difference in tank-to-tank driving unless you make it very large though (ie basjoos large).

Not sure what you're suggesting with the rear bumper extension. Post a pic?

I'm currently pics-disabled. Gotta get my own camera. Hopefully soon.

Anyway, for rear bumper: picture a foam cylinder about 8 inches diam, the diam equal to height of protruding bumper. It's as long as the bumper, across the car. Split it in half and stick it on back of bumper. For a better aero profile, use a triangle or a teardrop cross section instead of a split circle.

Aw shucks - you think the taper fin thing is not very noticeable in FE unless its several feet long? Come on, somebody tell me that a few inches helps. All these minivans have little spoilers like that. Sort of like a Kamm back concept - it's the teardrop taper without the end of the cone.

Generally I think everyone is open to possibilities. If you do this, you might use yarn to try to see what effect the shape or additions are having. Maybe you have an idea that hasn't been tested, or has been, but in a different form or on a different vehicle.

I'd love to find out if their is some flavor of what your suggesting that will make a noticable, measurable improvement. Give it a try and let us know.

>>Come on, somebody tell me that a few inches helps

It's a "every little bit helps" situation, but individually the positive changes are smaller than the margin of measurement error. Sure, do the back, do the grill block, drop the outside mirrors, do some wheel spoilers... maybe some skirts.... everything adds up and little and eventually you get your Cd down 4-5 hundreths and you see a difference.

^^ yup, what he said :)

Re: the back bumper - I think it's unlikely that extending it will help at all, since it's already fully in turbulent air.

In my opinion, you stand to see larger gains from rear wheel skirts than a roof extension, but as lca13 says, every little bit helps. It's not an "either or" situation - do it all!

Thanks guys.
Bit by bit - it's getting better.
Original EPA was 19/24. Revise that down by 20% or so for a "modern" EPA number! I'm getting about 30ish now in decent conditions.

Hi brucepick...I used your URL on TBricks to find this place.

My 245 has been deracked & plugged. My highway fuel economy went up almost instantly when I did it last Summer. In March, I added a "JSP Katana" rear lip spoiler to the top hatch. Its fairly small and unobtrusive(39"x1.5"), but I'm not sure if the "M3" design will have any drag reduction benefits when mounted in such a high position.
I'm hoping to be able to mount a more efficient front spoiler and lower the car eventually.

Hello SL8Brick - good to see ya. I hope you'll consider a front air dam extension with forward belly pan like what I did. Before that, glides were more like a rapid drop in speed than a glide. The belly pan part is important: it forces the plywood to the curve shape and cleans the underbody air flow considerably.

I have to say though that basjoos suggested that a front nose like his would probably help more. I think he's prolly right. Considering the shape of the 240 front end, a basjoos approach would probably extend 2' beyond the bumper so that design is not for the faint of heart. In Forums, search for posts by him (basjoos). Then find his car in Garage here.

basjoos, what do you think about the rear spoiler idea?
Basically I'm attempting a Kamm back concept there. Angled surfaces to continue the downward taper of the roof and the inward taper of the two sides.

I think the spoilers would be about 2-1/2 inches "wide", that is from front to rear. That's what you could carve out of a 2x4.