Aerodynamic Aids -- wings, spoilers, air dams, deflectors.

Capt. Mike

Transferred to create new topic.

deedu Member Posted September 14, 2006 09:57 PM

I apologize in advance if this is posted in the wrong area/listing, but it does have to do with aftermarket and roofs, and after looking through the rest of the listings this seemed like the best place.

I have an 87 Westy with a fairly-newly rebuilt engine that gets 20-23 mpg, depending on head/tail wind, speed, etc. With gas this year being rather expensive, and realizing that driving a westy is pushing (and pulling) a lot of air, I've wondered if anyone has tried putting a "spoiler" on the rear of the poptop. These (supposedly) cut the vacuum created from the van moving along by pulling some of the air passing across the roof down into the space behind the van. The result is (hopefully) better gas mileage. I see these on much newer vans and SUVs (ugh), so I assume they're not there just to "look cool". I've looked on the GoWesty and a few other sites but have yet to find them advertised for westies. I'd think aftermarket spoilers for other vans, which could be clamped/bolted on to the back edge of the poptop, would work. Any experience with such, or information sources on how much gas one might save - in terms of whether it would be worth the trouble? Thanks in advance!
cheers, deedu

Capt. Mike

Car Body Design has some interesting articles in their Technical Articles > Automotive > Aerodynamcs pages. They are a bit technical but two deal with rear airflow and a third with particulate behavior at the rear of a vehicle.

Anything that reduces the co-efficient of friction, or drag factor, on a vehicle, particularly a large squarish one, can reduce power required and increase fuel mileage. but at what cost and to what effect? Even EPA doesn't have any good research on the subject. They determined aerodynamic effects (wedge or slop-nose) on a trailer could increase mileage 5% at 55mph, but that's far removed from a van.

Wings are solely to increase downforce. A rear wing could increase downforce on the back of a van. Not unthinkable on the nose-heavy Detroit iron, but of marginal value on a rear-engine Westy that is already quite well balanced. If the Westy would go fast enough to work, it could also disturb the under-vehicle airflow and make it nose light for less stable steering. Remember, nothing is free.

Spoilers are to disrupt air-flow and can have several functions. I think you'll find that all the cute wings & spoilers on vans are mostly for visual effect and styling. Yes, they may help but do they offset the disadvantages (height increase, weight) and do gains exceed costs in typical driving use? A higher wing may bar you out of some parking decks, shops and garages. Jury is (far) out.

The amount a spoiler at the roof edge will decrease the vacuum suction at the rear of a Westy, even at 55 mph, is probably not going to materially affect your mileage. How much will it take in fuel savings to pay for a $200-400 spoiler? Adjusting for the fact that at low speeds it may hurt due to increased drag/downforce and probably only achieve any increases in efficiency at full highway speeds. Westies rarely get that 'mostly highway' use.

The most popular of wings/spoilers are for rear window deflection. By moving the vacuum effect back slightly, they do reduce the amount of road dust & grime that accumulates on the rear window. Some deflect an airflow directly across the rear window. theoretically keeping dirt from landing. I don't doubt both help. But so does my rear wiper & washer! Installing that on a Westy that didn't come with them may be as practical as the air damn.