Wheel Well Covers Greatly Disappointing

[Mr Incredible]

After much fussing and fitting I made some nice sheet steel (20ga) skirts for the rear wheel wells on the CRX. They stuck out no more than required to clear the wheels--not more than an inch away from the wheels. They fit snugly in the opening and the attachment points were solid and sufficient.

Results - 10mpg less than without. Repeated 50mpg w/out. Repeated 40mpg with. I even tried air deflectors under and in front of the rear wheel wells. No change.

Oh, well. I can cut them up and use them for sheet metal repairs prior to painting it this summer.

And I was SO hoping they would do better. They did look cool, though.

[RoadWarrior]

Wow...

Gut feeling theory on that is that they stopped air getting round behind the wheel and filling base drag vacuum from underneath. Weird.

[flapdoodle]

Thanks for sharing that. The things that don't work are just as important as the things that do.

[Drag Limited]

have any pictures?

[101mpg]

I agree - it's important to find things that don't work just as much. I've toyed with the idea of a teardrop shaped CRX - move the wheels in like on the Insight so there is a smaller rear track, with covered smooth outside wheel whells with removable covers - I think that your failed experiment is just more fuel for checking if it DOES work in another mode.

Thanks for the reporting - it helps out others too!

[Mr Incredible]

I didn't take any pictures while they were on. However, for those that may benefit by them I'll get a photo or two of how they were made and attached. Perhaps in the next few days...

[8307c4]

Ouch, well you saved me $100 if that makes you feel any better I've made a few mods that were as much a waste of time (electric fan conversion was one of them thou I didn't LOSE mpg).

I also don't think WOT or heavy acceleration saves fuel, and if it does it wears everything else out it's just not worth it, but the opposite sure is.

[cems70]

I installed some rigid cardboard rear wheel skirts in July '07 for my '95 Civic hatch w/ VX tranny. Same deal as yours...they only extended out as far as necessary to comforably clear the wheel, about an inch. Although I only left them on for one tankful, I felt they hurt my FE, although not as much as yours did. I got about 2.5 MPG less with the skirts on, with almost identical driving from one tank to the next. The car didn't feel like it coasted any better. I was very disappointed with the results because I really thought it would improve FE by about 5% based on the results of others w/ wheel skirts.

[RoadWarrior]

Oh by the way, wheels act somewhat like a centrifugal pump. When the surfaces following the back half of the wheel arch curve away, they may form a coanda surface which is in effect driven or pumped by the outflow from the wheel. This would entrain more air behind the vehicle than normally possible, and reduce base drag. This effect would not of course show up in a windtunnel unless the wheels were spinning... active aerodynamics!

However, if this is indeed the case then the effect might be enhanced by a baffle plate parallel to the axis of the vehicle, spaced a few inches off the vehicle... kind of shading the rear outer third of the wheel and continuing back until the curvature of the bumper or rear quarter drops away.

[eivad1]

well where the pics

[JanGeo]

Wow - interesting to hear this result as I was considering doing something with the rear wheel openings on my xB as well as a rear belly panel but now that this comes up it seems maybe some wind tunnel testing of a spinning tire is needed to see what actually happens to air flow around a tire. Guess the best thing would be smooth wheel covers? Even that may turn out to be false and funny if having air pumping outwards by bladed spokes resulted in lower drag.

[mustngr]

I had a similar experience with my Metro, which I attributed to an increase in "parachute effect". The covers were piling up air that would normally be exhausted through the wheelwells.

A rear belly pan solved this. I intend to vent the bumper to further release any accumulated air.

[bzipitidoo]

In another thread here I saw someone had not done just a grill block, they'd added louvered vents to the hood so air could exit the engine bay through the hood.

If you haven't cut your skirts up yet, maybe you could try adding louvers to the rear area. I've also wondered if a more open area behind the wheels could help.

[BamZipPow]

Looking at this blog they put in some ducts to vent the high pressure from the rear wheels. How open are the wheel wells towards the chassis? Piccies would help...

Also...what were the speeds you tested it at?

[Hateful]

Unlike the rest, I've been happy with my rear wheel skirts. They added a couple mph to rolling down a nearby hill in neutral starting at 40mph. I replaced the original duck tape with fake leather scrapes and galvanized wire.These do have a space in the back half for air to escape. I didn't plan it that way and now don't plan to fix it.