(Ugly) Aerodynamic Wheels
Discussion
I gather that reducing drag is an important part of efficiency for an EV hence the fitment of aerodynamic wheels, but pretty much invariably I find the design of such wheels quite ugly. What is it that makes a wheel aerodynamic, having a flat face?
I tend to favour more traditional designs like a five to ten spoke motorsportesqe style. What kind of difference would changing the wheels of a EV make to efficiency?
I tend to favour more traditional designs like a five to ten spoke motorsportesqe style. What kind of difference would changing the wheels of a EV make to efficiency?
xu5 said:
I gather that reducing drag is an important part of efficiency for an EV hence the fitment of aerodynamic wheels, but pretty much invariably I find the design of such wheels quite ugly. What is it that makes a wheel aerodynamic, having a flat face?
I tend to favour more traditional designs like a five to ten spoke motorsportesqe style. What kind of difference would changing the wheels of a EV make to efficiency?
Flat wheels allow the passing air to flow directly over/past the wheel and continue down the side of the car; where as traditional, more open designs would suck air into the wheel well and create a pocket of turbulent air, creating a small amount of drag. It's why high-end sports cars have functional vents at rear of the wheel well to allow trapped air to escape. I tend to favour more traditional designs like a five to ten spoke motorsportesqe style. What kind of difference would changing the wheels of a EV make to efficiency?
What I've never understood with the new generation of EVs is designers returning to the concept of enclosed rear wheels to max the aero dynamics; I gather this is based pretty much on design aesthetic and its a line most aren't willing to cross, despite all the other "progressive" design choices they decide to push out there.
Theres so much at play with aerodynamics for someone not involved in it it's really hard to even try to predict.
From my limited experience with designing high performance cars with heavy aero influence, wheel arch pressures play a huge factor. Having high or low arch pressures can make/break aero gains massively. Particularly where you're chasing higher levels of DF as it could completley kill or activate the floor which is where most downforce comes from.
In the projects I've been involved with arch pressure has been controlled with ducts, flow routes and bodyshape. At the speed we're chasing any discernable DF (80-180mph), the wheels are rotating at such a speed that they're basically treated as "solid" anyway. The vehicle velocity and airflow create much larger pressures than any wheel shape could possibly change.
Obviously that's a different aim to maximising efficiency, where you probably want it to be very neutral, but the floor and wheel arch pressures will play massively into that, especially at motorway/autobhan speeds. I would be really interested to know how specific wheel design changes arch pressures at road speeds, say 40-70mph.
From my limited experience with designing high performance cars with heavy aero influence, wheel arch pressures play a huge factor. Having high or low arch pressures can make/break aero gains massively. Particularly where you're chasing higher levels of DF as it could completley kill or activate the floor which is where most downforce comes from.
In the projects I've been involved with arch pressure has been controlled with ducts, flow routes and bodyshape. At the speed we're chasing any discernable DF (80-180mph), the wheels are rotating at such a speed that they're basically treated as "solid" anyway. The vehicle velocity and airflow create much larger pressures than any wheel shape could possibly change.
Obviously that's a different aim to maximising efficiency, where you probably want it to be very neutral, but the floor and wheel arch pressures will play massively into that, especially at motorway/autobhan speeds. I would be really interested to know how specific wheel design changes arch pressures at road speeds, say 40-70mph.
xu5 said:
What kind of difference would changing the wheels of a EV make to efficiency?
rigga said:
The aero wheel covers on Tesla cars don't look too bad.
The alloy wheels underneath look far far better though.
I read that removing the aero covers on a Tesla Model 3 wheels reduces the range by about 5%.The alloy wheels underneath look far far better though.
cuprabob said:
To be honest even the wheel designs on the majority of current ICE cars are pretty ugly in my opinion. I also don't get the obsession with diamond cut finishes which again in my opinion are not robust enough for last a UK winter.
Indeed, it will be nice when the trend for black and diamond cut wheels moves on. My oem diamond cut wheels have been relegated to winter use and will be getting powder coated as despite never being kerbed are absolutely covered in corrosion. Scrump said:
xu5 said:
What kind of difference would changing the wheels of a EV make to efficiency?
rigga said:
The aero wheel covers on Tesla cars don't look too bad.
The alloy wheels underneath look far far better though.
I read that removing the aero covers on a Tesla Model 3 wheels reduces the range by about 5%.The alloy wheels underneath look far far better though.
rigga said:
The aero wheel covers on Tesla cars don't look too bad.
The alloy wheels underneath look far far better though.
I disagree. The alloys look like some Halfords off the shelf bargain basement specials. The car was designed to have the aero covers so keep the aero covers on! (IMO)The alloy wheels underneath look far far better though.
An exception is the new model Y.....but i think that's because the trims they have on as standard are particularly grim...and the alloys look better....
Just IMO.
swisstoni said:
Much more to be gained by turning the a/c off than by a change of wheel design I would think.
With modern cars I'm pretty sure that's no longer true. I did some reading about this, and iirc the impact of the wheels, tyres and wheel arches can be about 25% of the total drag of a car. If you think about what an aero shape looks like, they're simply not easy to optimise for a smooth flow and no turbulence, compared to the rest of a car shape. You're trying to have smooth flow, and generally minimal turbulence, and an open set of spinning wheels essentially act like a fan creating turbulence.
There's relatively little available research on specifics, but the figure I saw a few times is that wheel choice can impact overall drag by as much as 10%, and broadly the more metal and the fewer gaps the better (assuming you don't want to go for narrower wheels or enclosed wheel arches). I took that 10% to be the difference between massive wheels with big gaps - 5 narrow spokes on some 20s for example - against something that's close to completely flat, with just enough gap for brake cooling.
There's a guy called Julian Edgar who's done some YouTube videos about this, I think one was based on some research Porsche published, and there's a chapter in his book about the impact of wheels (the rest of his book was quite interesting too).
I'm planning to change the 5 spoke 20s on my 640d for something more aero friendly, so will be interesting to see whether there's any noticeable difference in economy or acceleration.
I suspect far more could be gained by reducing the width of the tyre. That would provide an aerodynamic and rolling resistance improvement.
The 16 inch wheels (205/55 tyres) on my car would have been seen as too wide and low profile for an average car 30 years ago, and would only have been seen on the performance variant. These days they look like bicycle tyres compared to most vehicles in the supermarket car park.
The one bit I don't get though is why put plastic covers on alloy wheels. Alloy wheels with rubber band tyres really only became widespread on mainstream cars because they "look better" (or at least some people think so). If you're going to cover them up why not just have a steel wheel underneath.
The 16 inch wheels (205/55 tyres) on my car would have been seen as too wide and low profile for an average car 30 years ago, and would only have been seen on the performance variant. These days they look like bicycle tyres compared to most vehicles in the supermarket car park.
The one bit I don't get though is why put plastic covers on alloy wheels. Alloy wheels with rubber band tyres really only became widespread on mainstream cars because they "look better" (or at least some people think so). If you're going to cover them up why not just have a steel wheel underneath.
Evanivitch said:
SkodaIan said:
I suspect far more could be gained by reducing the width of the tyre. That would provide an aerodynamic and rolling resistance improvement.
Which BMW did on the i3 but only have limited tyre choices.E63eeeeee... said:
........I'm planning to change the 5 spoke 20s on my 640d for something more aero friendly, so will be interesting to see whether there's any noticeable difference in economy or acceleration.
That will be interesting, I guess any weight difference will come into it aswell.Gassing Station | General Gassing | Top of Page | What's New | My Stuff