Those wacky 9-X wheels
During the launch of the Saab 9-X BioHybrid, I referred a few times to the fact that the wheels were on the wrong sides. This may have led some to scratch their heads in wonder about whether or not I was off my rocker.
Here’s the car at the premiere event prior to the Geneva show:
And here’s a shot of the car at the show itself. It seems the Saab design people got busy with the trolley jacks after the premiere night 
The difference you’re looking for is in the fanning of the spokes. As you can see in the second shot, they’re drawing air in as the car goes forwards to aid in cooling the brakes. Whether or not this works in practice is another matter, but that’s the theory at least. Ubermich opined that it might actually create unwanted turbulence underneath car.
I hope they’re getting plenty of promotional shots with the wheels the right way around as all the pics from the premiere show it in just a slightly compromised fashion.
And should I say again how good this looks…….?
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I enjoyed the original 9x and am beginning to think this one is a step in the right direction. It looks good.
Just as a reference, remember the Aero-X:
http://www.vettochetikett.info/SAAB_AERO_X/index.htm
There was also discussion here, IIRC on the wheel direction. Maybe Saab is still working the logic out in their heads? It makes sense that air outside the car will be cooler, but you then run into the high-pressure vs low-pressure vs “not enough of anything to make a difference” pressure.
Naturally, the best way to find out will be to have two Aero-Xs (fully-functional and production-ready) side-by-side… And naturally, I hereby volunteer to drive one!
I’ll happily drive the other!!
All in the name of science, of course….
They should really draw air out as the wheel wells are usually a site of low pressure.
Those turbine wheels are just awesome. That’s exactly how they should appear in production.
As far as air flow goes with these wheels, it’s just engineers playing with numbers. In real life, it makes little difference. Axial-flow fans (the wheels would be in this family of fans) have a very low pressure rise anyway, and at a high angle of attack (air passing almost perpendicular to desired flow would qualify) the fan would be in “stall” — an operating region where nothing moves because the inherent pressure rise is offset by opposite forces predicted by convertional fluid dynamics (this force related to centrifugal force) and by Bernoulli’s Law (the principal that lets airplanes fly).
On the plus side, having them in stall would let the car travel without much additional drag from the wheels — if they were really pumping air under the car, the drag would be significant.
Plus, they’re
butt-uglybeautiful. I want some!!I can edit your stuff too, pal
Do production cars have different wheels on the left and right side? You need that in order to make the fans move air the same way on both sides of the car, don’t you?
I really doubt that it makes much of a difference either way, but I wouldn’t make any assumptions on which way is better.
If the under-hood area is a high pressure zone (because of air being fed to the radiator/intercooler), it could make more sense to have the wheels vent outwards. Then again, the wheels probably don’t have much of a brake cooling effect, so they may be most efficient operating in a near vacuum (less drag).
There could be side-to-side differences as well due to component placement. One potentially important factor is that the wheels are not moving relative to the road at the bottom, but they are moving at twice road speed at the top…
The situation may be different in the rear, and it may vary depending on whether or not the rear diffuser is deployed.
I think that what is really needed is “active” wheels that provide minimum drag when the brakes are cool and maximum drag when they are hot. These should be controlled by a fuzzy logic algorithm taking into consideration outside temp, underhood temp, atmospheric pressure, underhood pressure, road speed, braking/accelerating force, cornering force, the proportion of engine braking to friction braking, atmospheric conditions (rain, snow load), dynamic and static weight distribution, the current cost ratio between brake pads and gasoline/E85 (extrapolated forward to the next service interval or refill), the GPS location (mountain or flat terrain), live traffic reports, radar-computed inter car distance, local noise regulations, and a few other factors (including an owner-provided “go fast vs. look good” weighting).
I’ve always been a fan of any turbine style wheels. I subscribe to the belief that they should be positioned to draw air out from under the car to create a vacuum to hold the car down. Also, you always want to draw heat away from the car. Whether or not it happens doesn’t matter to me. That’s just the way I think they look better.