Can the rims of a car affect the aerodynamic efficiency of a vehicle?

More specifically, is there a difference between rims that are closed, with no holes, and rims that have thin spokes, or rims that have angled spokes?

What I was thinking is if a car has rims with spokes that are like blades of a fan, can they pull out air from under the car to provide extra downforce, or the inverse, can they pull air in under the car to lower the downforce and reduce drag?

  • $\begingroup$ You need to look at what happens in cycling. The most aerodynamic wheel is one with no spokes but there is a problem with stability if there is a cross wind. So compare indoors momnium.com/world-beating-pursuit-bike with outdoors bikeradar.com/road/news/article/best-deep-aero-wheels-49390. Balanced this is having spokes contoured to channel air under a car and increase down force which will reduce aerodynamic efficiency but improve cornering stability. $\endgroup$ – Farcher Dec 15 '17 at 7:50
  • $\begingroup$ Thanks @Farcher, I wondered as well watching the Olympics why the wheels are solid :) On another note, I found an f1technical forum thread talking about this a bit here. It seems a fan pulling air out from the wheel wells would lower drag because air creating turbulence in the wheel wells would decrease, cleaning up airflow. PS I edited 3 times to fix the link and add this bit ;) $\endgroup$ – Sam Chamberlain Dec 15 '17 at 16:45

This idea may contribute to increasing or decreasing downforce, depending on the profile of the blades.

You don't give a speed range, and I'm not sure how this would compare with the downforce generated by underbody fairings, but it's not allowed under FIA rules.

enter image description here

The Brabham BT46 fan car was banned (as it was too damn good), and if you like you could compare the angular velocity of the car's 4 wheels with that of the fan. I think this is a good argument for saying you might be on to something, but although it's easy to work out the wheel speed, I can't find anything on the angular velocity of the fan.

This is getting into EngineeringSE territory, but as I am an F1 fan (sorry) myself, I can't resist a picture to allow you to compare diameters.

The FIA ban might suggest that it is a potentially effective idea, but that it is also inherently dangerous as, at high speed, you don't want one corner of the car to unbalance an otherwise symmetrical distribution of downforce if the wheel blade profiles are not matched properly.

  • $\begingroup$ or if you lock one wheel $\endgroup$ – tfb Dec 15 '17 at 8:38
  • $\begingroup$ I loved the BT46, it's my favorite in F1 history! Thanks for the answer, that really helps settle the question for me, with the downforce symmetry and all. $\endgroup$ – Sam Chamberlain Dec 15 '17 at 16:38
  • $\begingroup$ Hi Sam, welcome to PSE and thank you. It's a half engineeringSE, half physics problem. This is not physics related, but about a year ago I was in Portugal and a car pulled up beside me at traffic lights. His wheel rims were still going around, even when stopped. He must have had tiny electric motors driving the wheel covers, to impress his friends....or something :) $\endgroup$ – user178231 Dec 15 '17 at 17:58
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    $\begingroup$ Countto10 that car I believe had what's called spinners on the rims. Once moving the spinners start to spin up from friction and whatnot, so once he pulled up to the light, the spinners were still rotating though he was stopped. I think spinners are dumb anyways \_('_')_/ $\endgroup$ – Sam Chamberlain Dec 15 '17 at 18:05

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