I've actually just started planning a video about this, specifically looking at the tires effect as the latest models from the tire manufactures show huge savings due very small changes in the sidewall profile or smoothness. Maybe we ought to have a chat sometime
For the Tesla Model 3 we worked with Michelin specifically to sculpt the tyre shoulder shape and sidewall detail for an aero benefit. They joked that it was easy enough for them to do, but nobody had asked before.
So, I tried it out. 80% front wheel covers only, plus 50% upper and lower grille blocks, and fog light tape over. My usual to work trip, 26kms highway/4kms city… I used 22kms of fuel instead of my usual 28-30kms depending on amount of stop lights. This is in a 2015 Mazda cx-5. Thank-you!
Just found your youtube channel. I remember the name and dug out my very old copy of 21st Century Performance to confirm. Good to see you're still at it. Still remember your R32 GTR with centre diff potentiometers.
Lots of books since 21st Century Performance... www.amazon.com.au/stores/author/B00C3MRYN4/allbooks?ingress=0&visitId=05bf8335-6517-4f50-a6d2-c55ac1ce2caa&ref_=ap_rdr
I remember once you made a video about a porsche patent that redirected hot air from the cooling system to the front of the wheel. that improved both cooling but also decreased drag. I just cant find the video but i do remember you talking about that.
Im lucky with my car, that I still have steel rims. With that I was able to mount Mooncaps. This alone helped reduced drag and also reduced Fuel usage (only by 0,1-0,2L/100km, but its something!). Same I am going to try with narrow tires, since I need new tires anyway. Just bought two of your books and very love the detailed Information in there! Hats off and Thank you!
As I thought, the factory wheels that Honda fitted to their cars, thinking of your Insight, and my 4WS Accord. Good to know, and thanks. Excellent video, mate.
Hi Julian ! I learned tonnes of technical info and aerodynamics from your articles in AUTOSPEED mag some years back. Thank you Sir for that education🎉🎉❤
I finally bought your book! Both this and the history of aerodynamic work on car designs. I've been watching your videos for some time, studying to apply relevant principles to electric motorcycle streamlining for range increase. It has been very tricky to apply lessons, as a lot of the constraints, proportions, and circumstances are different, but I definitely want to say I appreciate what you do, and that videos like this are very good exposure for people to what factors use up power in their cars.
I just found your channel and am looking forward to going through it! This is important content: no frills just good explanation and interesting topics.
I have all you books and absolutely love them. I have enacted a lot of little bits on my own dirt speedway race car with great results. How about a focus video on what us dirt racers can do to reduce lift from air getting under the roof of the car (no windows)?
It's crazy how basically no company addresses this but Tesla with their drag reducing covers Thank you so much Julian I'm so glad there's someone out there who is honest and actually knows what they are talking about.
If you look at the wheels on a lot of electric cars the rims have a lot of flat surface on the outside with smaller gaps in between the spokes. I think there's an attempt to make more aerodynamic rims while keeping a normal look so as not to alienate buyers. Even Tesla's covers tend to be black and blend in.
I have seen quite a few cars over the years with drag reducing wheels, both subtle and not They're especially prevalent on EVs though given the smaller amounts of energy they carry
@@robinrai4973 this is true the insight another vehicle Julian has I believe has aero wheels. How ever what im saying is Tesla are pulling the people into it by giving them that hot swap ability and they give ROLLING cds as well rather than just drag coeffiicne f
Measuring changes in drag with wheel covers is marginal in on-road testing. Pressure and tuft testing give you an indirect picture of what is going on.
intersting insights! i am especcialy curious about how the mclaren at 6:13 seems to have stationary covers in the front, i wonder how much the not spinning of the covers affects drag.
Just purchased your book on Amazon, should arrive on Saturday. What % of vehicles would you anticipate full smooth wheel covers would not being beneficial? I have a quite slippery vehicle, the ioniq 6-and the base model wheels are much more efficient than the spoked 20” wheels on my trim level. Thanks for the video!
Would you consider having a digital version of the book? I agree the turbo wheel covers look cool, I made myself some on a 3d printer. Doubt that they help with aero much, since I made them stand out by about 30mm, maybe someday I'll try to make real aero ones.
@JulianEdgar at 4:48 in the video you discuss a technical paper on the design of the Tesla Model S wheels which I also have on my Tesla Model X. The problem with them that has been discussed since the wheels were released is that if they are designed to be extremely aerodynamic they forgot to reverse the pattern for one side of the car because on the passenger side the flat edge of the blades faces forward which should be creating far more drag on that side than the drivers side. Wouldn't you agree? I will test with tufts of yarn on both sides to see the difference.
Very interesting. I am curious if you tested a smooth wheel cover that covers the edge of the wheel inward but leaves the center open vs the design with pizza dish covers that cover the center of the wheel outward but leaves the outer edge of the wheel open? Is there a difference in cooling or drag with different designs? I am also interested in the inflatable front air dam as used by Porsche a few years ago and how it would benefit reducing tire drag but also increasing total frontal area when inflated. I assume it would help keep the air flow smooth around the front and into the sides of the vehicle more than any added frontal area increase for a net benefit. Great channel and I look forward to getting your book.
We studied this for the (notorious) Aero Wheels on the Tesla Model S. Whether rim perimeter or rim hub closure is better depends quite a lot on the design of the vehicle's whole front quarter, and how much transverse flow there is through the wheel & wheelarch cavity. If the bulk of the flow is longitudinally aligned, then perimeter closure is better. If there's a strong lateral component, then hub is better. It has to be optimized as a system, not a bolt-on performance item.
Julian, as a fellow Aussie I would like you to contact Carbon Revolutions. They make Carbon fibre wheels but none are aerodynamic and therefore few people with EV's would consider their wheels (and many stock wheels on EV's are either ugly or not very aero). If they made aero carbon wheels I believe they would sell like hotcakes.
I was once a fan. These days, watching how they promote the vehicle and solicit $$, I wouldn't give them the time of day. Hopefully I am quite wrong, but we will see.
Would be active ventilation for the brakes a solution to better cover the wheels? With temperature controlled fans blowing a the brakes, it also would have the advantage, that cooling can continue at stop or low speed driving, while self ventilated brake disc only cool at higher rotation speed.
Recently retired and building a camper to go on the back of my truck. I'm trying to find information about aero and sharp/curved edges with an eye to rounding all edges to allow for better aero. From another of your videos, you mentioned rear spoilers with sharp edges for clean seperation, but I cant seem to find info on how rounded frontal/side edges should be. Any suggestions on publicly available info? thank you.
I strongly suggest you buy the book - the money you save by making the correct decisions in the camper build will pay the cost of the book many times over. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8
What's your take on wheel spat attached to the bodywork rather than covers on the rear wheels? I have a theory that turbofan style covers on the front wheels only to actively evacuate air from the front paired with bodywork mounted rear spats and an undertray would generate overall improved performance.
Does the exhaust outlet have a lot of influence on aerodynamics? Does its position influence the gas output? Old nascars use the barrel at 45 degrees, modern ones are straighter in relation to the body.
The exhaust has very little effect. The exhaust volume is low relative to the air passing the car, and the exhaust volume also varies with engine load.
For an enthusiast, would there be a setup possible with a spinning wheel and measuring wind speed in certain positions ? Would such a setup be viable/useful to come to some conclusions and see what design of wheel causes least drag ? Or can it only be measured on the car itself ?
As I describe in the video, one cause of wheel drag is how the wheel's flow disrupts / changes flow on the car. Testing in free air probably ignores 75 percent of what is actually going on (even ventilation drag is affected by the presence of the car).
Definitely getting moon discs on my next car, even if they were to inadvertently increase drag - the cool factor would more than make up for it! Also love cars with enclosed rear wheel fairings - that should come back. Love the air suspension that lowers with speed as well.
What about removable covers that cover the entire rear wheel wells? Slightly less convenient to change the wheel but would retain the body shape throughout the rear quarter.
“Fender skirts” were used on big American cars in the 1950’s and 1960’s but they only covered about ½ the exposed wheel/tire. They were for appearance only, allowing the stylists to continue their visual design rearwards without the wheel opening interrupting. They were also available as aftermarket add-ons, along with exterior sun visors over the windshield and rubber mud flaps with your choice of symbols or cartoon characters, oh, and reflectors.
At around 9:50 there is a loud “ding!” noise. I thought I’d received a text. So I ran the video back and sure enough, it was YOU. April Fools joke? Ya got me.
My old pre-facelift benz w124 had aero style flat hubcap and some say it helping cooling the brakes, but my question is can this cooling effect and hubcap fin design ruined aerodynamic?
@@JulianEdgar I can not attach pictures of CFD analysis but the old little notchbacks like the Toyota mr2 aw11 notably has a sharp edge and seperation at the leading edge of the roof, creating a big low pressure and also making most aero work at the back of the car useless.
I have read that if the bottom of a vehicle was smooth, increasing ground clearance helps lower drag. But if the surface is uneven, then lowering the vehicle is better? It seems counter-intuitive to me that difference a small difference in the frontal area of tires, in proportion to the rest of the vehicle, would make any meaningful difference?
If rear wheel covers don’t do much to help keep flow attached to the body behind the wheel, why did you put them on your Nismo? There’s not much body after the rear wheels on it.
@@Y2Kvids the large tread blocks behave like scoops trying to move the air which creates heaps more drag. while the slick has no tread to interact with the air. yes their frontal area is the same, but their drag values will be very different at speed.
@@JulianEdgar the shiney part around the edge is the lip, fat because it's wide... ie, my car has 3-piece 18x9 wheels with +11mm offset, so there is ~3" of polished aluminum between the tire & painted wheel face.
@@JulianEdgar less face in the airflow, yes, and if the wheel is pumping air from behind then face (under the car), then the wheel won't be interfering with airflow directly. it will be in a low pressure area, & less pressure = less drag
Turbofans are essentialy just plates you put on top of normal rims to get more of an aerodynamic shape Similar to those used in time attack bikes, but not as effective, I would assume Also similar to the makeshift ones you showed in the video
I did a quick search and it shows a fan-like arrangement behind the flat covers. That will massively increase ventilation drag. bimmerlife.com/2022/08/21/turbofans-are-the-best-hubcaps/
Have you seen those panels on large 18 wheeler trucks? They put them behind the wheels to push the wheel wake outboard. When you do that to a wheel, the wheels turbulence turns into a coherent vortex, which has less drag, and makes the wake easier to manage, keeps it from getting under the body, which increases downforce, as there's less turbulent mixing from the tire wake with the fast moving flow under the body of the trailer. This also works in cars, you can achieve this two ways, by outwashing airflow behind the tire, or adding static toe out to your alignment. Of course the former is preferable because using toe out makes a car harder to drive and affects tire wear and rolling resistance.
Do you have any evidence (peer reviewed papers or textbooks) that support what you have said here? There appears to be multiple problems with your comments.
@@JulianEdgar Start here "COMPUTATIONAL INVESTIGATION INTO THE INFLUENCE OF YAW ON THE AERODYNAMICS OF A ROTATING WHEEL IN FREE AIR" Then this: Computational Investigation of the Combined Effects of Yaw, Rotation and Ground Proximity on the Aerodynamics of an Isolated Wheel Then this: The Effect of Camber and Yaw Angle on the Aerodynamic Performance of Rotating Wheels in Contact with the Ground I'm afraid CZcams won't let me link my own data, or the papers directly. This should help you get started, good luck.
@@JulianEdgar But you don't have to trust me, or peer reviewed CFD studies, or the fact that Porsche and BMW are putting out washing vanes behind the front wheels on their latest performance cars. They could just be doing it for ships and giggles. You can do your own measurements and prove it for yourself. It'll be great content for your book/youtube channel.
The first paper, and the second thesis, are about rotating wheels in free air - irrelevant to road cars, that don't have rotating wheels in free air. The final thesis shows that yes, camber and toe impact aero drag - not surprising (however, again it appears to show the modelled wheel in free air). None of your cited references support what you said in your comments.
@@JulianEdgar Well to that I say that trailers on transport trucks are free wheels, they have mud flaps but are otherwise in free air. Furthermore, I know you know that angle of attack isn't relative to the true dead ahead, but relative to the direction of flow. You've even made videos about it. Now consider that moving airflow outward by 15 degrees relative to the wheel, would in essence be the same as having the wheel toed out 15 degrees, and perfect axial flow. The relative interaction with the wheel and the air would be the same. Therefore aerodynamically out washing air behind the wheel, changing the flow path and relative motion of air across the wheel, will produce the same effect as yawing out the wheel. Again, you don't have to take my word for it, you can test it yourself, I mean the trucking industry is doing it for a reason. Porsche and BMW is doing it for a reason. Actually most modern cars, almost like this is a recent discovery. Then again this has been the ethos of most race car aerodynamics in the prototype class, it's all about out washing the wheel wake with bodywork.
I read "The Aerodynamics Development of the Tesla Model S - Part 2: Wheel Design Optimization" paper and got a few points from it: 1. Reducing the rotational moment is part of overall efficiency and contrary to a fully covered wheel 2. A covered wheel increases pressure inside the wheel, which adds a lot of lift 3. A more exposed wheel can energize air flow, which can reduce the functioning of diffusers (like in czcams.com/video/hgXni_LUgwc/video.html ), but might be desirable (e.g. at the front of the car?) Is this right? Makes it seem like a covered front and open back is better on a car without a good diffusers (Speedtail), since it gives rear downforce; but otherwise front and back each have good reasons to be covered or not...
It's a good paper but its conclusions apply only to the car in development - the Tesla Model S. As one of the authors of the paper (Rob Palin) said in his comments here yesterday, the wheels have to be optimised as part of the car system, not as bolt-on performance items. It's why in my book I always look at multiple technical sources (papers and books) before drawing conclusions. The recommendations I make in the book regarding wheels are based on many sources, not just one.
Has anyone actually done the opposite, and to deliberately send airflow into the wheelwell, and thus cool the brakes? I've had a mild idea that the wheel itself could be designed to work like a fan, with blades, to suck cool air into and over the brakes.
That's so funny, I had this thought just today as well. I think the idea is to pull air from underneath the car and out through the wheel rather than push it in. This might be because there is a pressure differential between the high pressure floor area and the low pressure wheel well. As for the fans, I think thats what the 80s rally cars were doing with the turbofan wheels. Hi from Australia
@@JulianEdgar You mentioned in another video that by lowering the floor under the engine bay you were able to generate a high pressure region and get a bit of a venturi effect. This is no doubt covered in your book ;) I haven't bought it yet but I subscribed to your channel as a reminder a while back.
Thought you might get a kick out of the moving front wheel spats on my RX7. It's primarily aesthetic, but also intended to reduce drag. czcams.com/video/B-Mk5TCV0VQ/video.html czcams.com/video/qbSDIWw-zxQ/video.html Anyway, was just going through some of your videos thinking about making some type of front air dam to help increase pressure for the bottom feed radiator, and considering the trade off for increased drag. I intend to do a flat bottom and rear diffuser next, would hate to disrupt the under car flow too much. Better buy your book before that 😁
I've actually just started planning a video about this, specifically looking at the tires effect as the latest models from the tire manufactures show huge savings due very small changes in the sidewall profile or smoothness. Maybe we ought to have a chat sometime
Oh hey, one of my two favorite channels! Glad to see you here! :)
Yes yes ❤ you guys need to chat
For the Tesla Model 3 we worked with Michelin specifically to sculpt the tyre shoulder shape and sidewall detail for an aero benefit. They joked that it was easy enough for them to do, but nobody had asked before.
Love your channel! Can we put in a request for a tire efficiency test!
Push bike tyre have been developed for aerodynamics for at least a decade.
nooo RIP the aero Insight 😭
It's still alive; just parked and no longer registered for the road.
@@JulianEdgar woo! compete in motorkhanas with it! there's one on this sunday at Nirimba Tafe
Did you cover the efficiency gains from the aero mods in one of your videos?
No, because most of the aero mods were aimed at gaining downforce. Those results are quantified in my book.
So, I tried it out. 80% front wheel covers only, plus 50% upper and lower grille blocks, and fog light tape over. My usual to work trip, 26kms highway/4kms city… I used 22kms of fuel instead of my usual 28-30kms depending on amount of stop lights. This is in a 2015 Mazda cx-5. Thank-you!
Nice, but fuel consumption testing needs to be done over a very long distance to give you certainty in the results.
@@JulianEdgar yes, understood. I unfortunately do not drive long distances so I do not have a good gauge of what a long distance mpg would be.
30%, I would have never thought that. Every day is a school day. Great info as usual Julian.
Just found your youtube channel. I remember the name and dug out my very old copy of 21st Century Performance to confirm. Good to see you're still at it. Still remember your R32 GTR with centre diff potentiometers.
Lots of books since 21st Century Performance... www.amazon.com.au/stores/author/B00C3MRYN4/allbooks?ingress=0&visitId=05bf8335-6517-4f50-a6d2-c55ac1ce2caa&ref_=ap_rdr
I remember once you made a video about a porsche patent that redirected hot air from the cooling system to the front of the wheel. that improved both cooling but also decreased drag. I just cant find the video but i do remember you talking about that.
Yes, and covered in detail in my book on the history of car aero - www.amazon.com/Century-Car-Aerodynamics-science-airflow/dp/B095RLP52B
I’ve always thought the bmw i3 had very skinny tires. Now it makes sense! Great video!
Wow super underrated channel. This was great stuff man.
Glad you think so!
Im lucky with my car, that I still have steel rims. With that I was able to mount Mooncaps. This alone helped reduced drag and also reduced Fuel usage (only by 0,1-0,2L/100km, but its something!).
Same I am going to try with narrow tires, since I need new tires anyway.
Just bought two of your books and very love the detailed Information in there! Hats off and Thank you!
Yes! Moons! Nobody seems to remember them.
Thank you
that’s about 3% so still something
The video highlighted moons in the middle, regarding salt flat racing. He even says full covers are less effective than partial.
So what your telling me is gm salad shooter wheels not only look good but are the best aerodynamically
As I thought, the factory wheels that Honda fitted to their cars, thinking of your Insight, and my 4WS Accord. Good to know, and thanks.
Excellent video, mate.
Hi Julian ! I learned tonnes of technical info and aerodynamics from your articles in AUTOSPEED mag some years back. Thank you Sir for that education🎉🎉❤
No problem. AutoSpeed is a long time ago in the context of what I've been writing in the last few years.
I finally bought your book! Both this and the history of aerodynamic work on car designs. I've been watching your videos for some time, studying to apply relevant principles to electric motorcycle streamlining for range increase. It has been very tricky to apply lessons, as a lot of the constraints, proportions, and circumstances are different, but I definitely want to say I appreciate what you do, and that videos like this are very good exposure for people to what factors use up power in their cars.
Glad you like them!
I just found your channel and am looking forward to going through it! This is important content: no frills just good explanation and interesting topics.
Welcome aboard!
Amazing as always, legend!
I have all you books and absolutely love them. I have enacted a lot of little bits on my own dirt speedway race car with great results. How about a focus video on what us dirt racers can do to reduce lift from air getting under the roof of the car (no windows)?
It's crazy how basically no company addresses this but Tesla with their drag reducing covers
Thank you so much Julian I'm so glad there's someone out there who is honest and actually knows what they are talking about.
If you look at the wheels on a lot of electric cars the rims have a lot of flat surface on the outside with smaller gaps in between the spokes. I think there's an attempt to make more aerodynamic rims while keeping a normal look so as not to alienate buyers.
Even Tesla's covers tend to be black and blend in.
I have seen quite a few cars over the years with drag reducing wheels, both subtle and not
They're especially prevalent on EVs though given the smaller amounts of energy they carry
Thank you
@@robinrai4973 this is true the insight another vehicle Julian has I believe has aero wheels. How ever what im saying is Tesla are pulling the people into it by giving them that hot swap ability and they give ROLLING cds as well rather than just drag coeffiicne f
Hyundai and Mercedes also put a lot of RND into aero rims for some of their models. Namely the Ioniq line from Hyundai and the EQS from Mercedes.
Amazing!
Thanks!
Yiss! Been looking for this
Good show. Would love to hear in a future video by how much these contraptions were measured to reduce the drag on the cars you've modified
Measuring changes in drag with wheel covers is marginal in on-road testing. Pressure and tuft testing give you an indirect picture of what is going on.
hmmm 🤔 may be then a simple MPG (km/L) average would be a cool thing in some future content 😅
Covered in my book - basically of no use without averages over huge distances.
intersting insights! i am especcialy curious about how the mclaren at 6:13 seems to have stationary covers in the front, i wonder how much the not spinning of the covers affects drag.
Huge!
I put some fender skirts on my car. Now I'm contemplating putting a moon disc cover on the rim behind the fender skirts.
The ecomodder forums have some fairly modified vehicles and many of them forego the rear covers once arch covers are installed.
Just purchased your book on Amazon, should arrive on Saturday. What % of vehicles would you anticipate full smooth wheel covers would not being beneficial? I have a quite slippery vehicle, the ioniq 6-and the base model wheels are much more efficient than the spoked 20” wheels on my trim level. Thanks for the video!
Read the book's section on reducing wheel and tyre drag and then you'll have a better idea as to the answer to that question. It's not simple.
I'd love to build an aero CR-Z
Would you consider having a digital version of the book?
I agree the turbo wheel covers look cool, I made myself some on a 3d printer. Doubt that they help with aero much, since I made them stand out by about 30mm, maybe someday I'll try to make real aero ones.
No, digital books get pirated within hours. I am not greedy, but I need to earn something.
@JulianEdgar at 4:48 in the video you discuss a technical paper on the design of the Tesla Model S wheels which I also have on my Tesla Model X. The problem with them that has been discussed since the wheels were released is that if they are designed to be extremely aerodynamic they forgot to reverse the pattern for one side of the car because on the passenger side the flat edge of the blades faces forward which should be creating far more drag on that side than the drivers side. Wouldn't you agree? I will test with tufts of yarn on both sides to see the difference.
It might make a *tiny* difference.
Who knew pizza dishes had such a cyberpunk vibe.
Very interesting. I am curious if you tested a smooth wheel cover that covers the edge of the wheel inward but leaves the center open vs the design with pizza dish covers that cover the center of the wheel outward but leaves the outer edge of the wheel open? Is there a difference in cooling or drag with different designs? I am also interested in the inflatable front air dam as used by Porsche a few years ago and how it would benefit reducing tire drag but also increasing total frontal area when inflated. I assume it would help keep the air flow smooth around the front and into the sides of the vehicle more than any added frontal area increase for a net benefit. Great channel and I look forward to getting your book.
Road testing of different wheel covers is not sufficiently accurate to show measurable differences between such subtle changes.
@@JulianEdgar So would only a rolling road wind tunnel test be accurate enough to find what works better?
Good question. I don't know - the experts tell me that accurately measuring wheel drag in wind tunnels is very difficult indeed.
We studied this for the (notorious) Aero Wheels on the Tesla Model S. Whether rim perimeter or rim hub closure is better depends quite a lot on the design of the vehicle's whole front quarter, and how much transverse flow there is through the wheel & wheelarch cavity. If the bulk of the flow is longitudinally aligned, then perimeter closure is better. If there's a strong lateral component, then hub is better. It has to be optimized as a system, not a bolt-on performance item.
Julian, as a fellow Aussie I would like you to contact Carbon Revolutions. They make Carbon fibre wheels but none are aerodynamic and therefore few people with EV's would consider their wheels (and many stock wheels on EV's are either ugly or not very aero). If they made aero carbon wheels I believe they would sell like hotcakes.
I'd like to know what you think of the "Solar powered" aptera, that thing was designed to be aero and efficient!
I was once a fan. These days, watching how they promote the vehicle and solicit $$, I wouldn't give them the time of day. Hopefully I am quite wrong, but we will see.
Would be active ventilation for the brakes a solution to better cover the wheels? With temperature controlled fans blowing a the brakes, it also would have the advantage, that cooling can continue at stop or low speed driving, while self ventilated brake disc only cool at higher rotation speed.
Yes, that's a good point.
Recently retired and building a camper to go on the back of my truck. I'm trying to find information about aero and sharp/curved edges with an eye to rounding all edges to allow for better aero. From another of your videos, you mentioned rear spoilers with sharp edges for clean seperation, but I cant seem to find info on how rounded frontal/side edges should be. Any suggestions on publicly available info? thank you.
I strongly suggest you buy the book - the money you save by making the correct decisions in the camper build will pay the cost of the book many times over. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8
Sr i have a question i found your books on amazon usa but id like to get them signed for my collection, is there away we can get that done??
The only way would be for me to send you a signed copy. But by the time you pay for the book and postage, that would likely be very expensive.
What's your take on wheel spat attached to the bodywork rather than covers on the rear wheels? I have a theory that turbofan style covers on the front wheels only to actively evacuate air from the front paired with bodywork mounted rear spats and an undertray would generate overall improved performance.
Yes wheel spats work well. But don't have theories - test, measure and develop. Guesswork / theories are usually wrong!
Ive often wondered if fitting wheels spacers noticeably increases drag by plasing your spinning turbine blades (wheels) more in the path of the air?
I've not seen any research on this but it is very likely to be car-specific. eg if the wheels are deeply inset, spacers may improve drag.
Does the exhaust outlet have a lot of influence on aerodynamics? Does its position influence the gas output? Old nascars use the barrel at 45 degrees, modern ones are straighter in relation to the body.
The exhaust has very little effect. The exhaust volume is low relative to the air passing the car, and the exhaust volume also varies with engine load.
To reduce drag, remove the nismo package 👍
Why?
@@JulianEdgar downforce is drag
So, equally, is lift.
For an enthusiast, would there be a setup possible with a spinning wheel and measuring wind speed in certain positions ? Would such a setup be viable/useful to come to some conclusions and see what design of wheel causes least drag ? Or can it only be measured on the car itself ?
As I describe in the video, one cause of wheel drag is how the wheel's flow disrupts / changes flow on the car. Testing in free air probably ignores 75 percent of what is actually going on (even ventilation drag is affected by the presence of the car).
Julian, how would attaching stiff rubber seals down the side of a car by the pitch welds (similar to PSNI Riot Land Rovers) affect drag?
The effect of side skirts is car-specific. Test and measurement is your answer (as it is with nearly every question that people pose here!).
Hello,
Which paper did you reference about the Tesla Model S wheel dsign aerodynamics?
best regards
www.sae.org/publications/technical-papers/content/2012-01-0178/
Definitely getting moon discs on my next car, even if they were to inadvertently increase drag - the cool factor would more than make up for it!
Also love cars with enclosed rear wheel fairings - that should come back. Love the air suspension that lowers with speed as well.
What about removable covers that cover the entire rear wheel wells? Slightly less convenient to change the wheel but would retain the body shape throughout the rear quarter.
Sure, you could do that.
“Fender skirts” were used on big American cars in the 1950’s and 1960’s but they only covered about ½ the exposed wheel/tire. They were for appearance only, allowing the stylists to continue their visual design rearwards without the wheel opening interrupting. They were also available as aftermarket add-ons, along with exterior sun visors over the windshield and rubber mud flaps with your choice of symbols or cartoon characters, oh, and reflectors.
At around 9:50 there is a loud “ding!” noise. I thought I’d received a text. So I ran the video back and sure enough, it was YOU. April Fools joke? Ya got me.
Not intentional... I just got a text.
My old pre-facelift benz w124 had aero style flat hubcap and some say it helping cooling the brakes, but my question is can this cooling effect and hubcap fin design ruined aerodynamic?
No, Mercedes has an excellent understanding of car aero, including on the W124.
@@JulianEdgar thank you for the information maybe it's better to keep aero caps than changing to gullideckel style wheels
could you make a video on how to deal with old car shapes with sharp windshield leading edges causing unattached flow and lift on the roof?
I’d need to see some evidence that’s a problem first. No car I have ever tested has flow separation on the roof.
@@JulianEdgar I can not attach pictures of CFD analysis but the old little notchbacks like the Toyota mr2 aw11 notably has a sharp edge and seperation at the leading edge of the roof, creating a big low pressure and also making most aero work at the back of the car useless.
You're looking at amateur CFD that is usually all wrong. Do some tuft testing - there won't be flow separation on the roof.
I have read that if the bottom of a vehicle was smooth, increasing ground clearance helps lower drag. But if the surface is uneven, then lowering the vehicle is better? It seems counter-intuitive to me that difference a small difference in the frontal area of tires, in proportion to the rest of the vehicle, would make any meaningful difference?
It's a complex topic, covered in my book. www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8
If rear wheel covers don’t do much to help keep flow attached to the body behind the wheel, why did you put them on your Nismo? There’s not much body after the rear wheels on it.
Just for appearance.
Any role of Thread pattern of the wheel .
Yes, tread does play a minor part.
the efficiency difference of a slick race tyre to an offroad mud tyre would be large
@@megamonkey56 in terms of air drag , the frontal are seem to be same
@@Y2Kvids the large tread blocks behave like scoops trying to move the air which creates heaps more drag. while the slick has no tread to interact with the air.
yes their frontal area is the same, but their drag values will be very different at speed.
How does a fat lip effect the aero of a wheel?
What is a fat lip?
@@JulianEdgar the shiney part around the edge is the lip, fat because it's wide...
ie, my car has 3-piece 18x9 wheels with +11mm offset, so there is ~3" of polished aluminum between the tire & painted wheel face.
@@JulianEdgar czcams.com/users/shortsaCr8wUMoL4E?si=XZAAGE7IIdvPWKBp
(makes alignment easier)
I'd call that 'dish' I think. The deeper the dish of the wheel, the less of a flat face it presents to airflow and so the likely higher drag.
@@JulianEdgar less face in the airflow, yes, and if the wheel is pumping air from behind then face (under the car), then the wheel won't be interfering with airflow directly. it will be in a low pressure area, & less pressure = less drag
All I'm hearing is "Turbofan rims work", so... Maybe I should get some
Not sure how you got that idea from the video.
Turbofans are essentialy just plates you put on top of normal rims to get more of an aerodynamic shape
Similar to those used in time attack bikes, but not as effective, I would assume
Also similar to the makeshift ones you showed in the video
I did a quick search and it shows a fan-like arrangement behind the flat covers. That will massively increase ventilation drag. bimmerlife.com/2022/08/21/turbofans-are-the-best-hubcaps/
@@Navoii. lol turbofan wheels is basically the opposite of what he was talking about
Have you seen those panels on large 18 wheeler trucks? They put them behind the wheels to push the wheel wake outboard. When you do that to a wheel, the wheels turbulence turns into a coherent vortex, which has less drag, and makes the wake easier to manage, keeps it from getting under the body, which increases downforce, as there's less turbulent mixing from the tire wake with the fast moving flow under the body of the trailer. This also works in cars, you can achieve this two ways, by outwashing airflow behind the tire, or adding static toe out to your alignment. Of course the former is preferable because using toe out makes a car harder to drive and affects tire wear and rolling resistance.
Do you have any evidence (peer reviewed papers or textbooks) that support what you have said here? There appears to be multiple problems with your comments.
@@JulianEdgar Start here "COMPUTATIONAL INVESTIGATION INTO THE INFLUENCE OF YAW ON THE AERODYNAMICS OF A ROTATING WHEEL IN FREE AIR"
Then this:
Computational Investigation of the Combined Effects of Yaw, Rotation and Ground Proximity on the Aerodynamics of an Isolated Wheel
Then this:
The Effect of Camber and Yaw Angle on
the Aerodynamic Performance of Rotating
Wheels in Contact with the Ground
I'm afraid CZcams won't let me link my own data, or the papers directly. This should help you get started, good luck.
@@JulianEdgar But you don't have to trust me, or peer reviewed CFD studies, or the fact that Porsche and BMW are putting out washing vanes behind the front wheels on their latest performance cars. They could just be doing it for ships and giggles. You can do your own measurements and prove it for yourself. It'll be great content for your book/youtube channel.
The first paper, and the second thesis, are about rotating wheels in free air - irrelevant to road cars, that don't have rotating wheels in free air. The final thesis shows that yes, camber and toe impact aero drag - not surprising (however, again it appears to show the modelled wheel in free air). None of your cited references support what you said in your comments.
@@JulianEdgar Well to that I say that trailers on transport trucks are free wheels, they have mud flaps but are otherwise in free air. Furthermore, I know you know that angle of attack isn't relative to the true dead ahead, but relative to the direction of flow. You've even made videos about it.
Now consider that moving airflow outward by 15 degrees relative to the wheel, would in essence be the same as having the wheel toed out 15 degrees, and perfect axial flow. The relative interaction with the wheel and the air would be the same.
Therefore aerodynamically out washing air behind the wheel, changing the flow path and relative motion of air across the wheel, will produce the same effect as yawing out the wheel.
Again, you don't have to take my word for it, you can test it yourself, I mean the trucking industry is doing it for a reason. Porsche and BMW is doing it for a reason. Actually most modern cars, almost like this is a recent discovery.
Then again this has been the ethos of most race car aerodynamics in the prototype class, it's all about out washing the wheel wake with bodywork.
I read "The Aerodynamics Development of the Tesla Model S - Part 2: Wheel Design Optimization" paper and got a few points from it:
1. Reducing the rotational moment is part of overall efficiency and contrary to a fully covered wheel
2. A covered wheel increases pressure inside the wheel, which adds a lot of lift
3. A more exposed wheel can energize air flow, which can reduce the functioning of diffusers (like in czcams.com/video/hgXni_LUgwc/video.html ), but might be desirable (e.g. at the front of the car?)
Is this right?
Makes it seem like a covered front and open back is better on a car without a good diffusers (Speedtail), since it gives rear downforce; but otherwise front and back each have good reasons to be covered or not...
It's a good paper but its conclusions apply only to the car in development - the Tesla Model S. As one of the authors of the paper (Rob Palin) said in his comments here yesterday, the wheels have to be optimised as part of the car system, not as bolt-on performance items. It's why in my book I always look at multiple technical sources (papers and books) before drawing conclusions. The recommendations I make in the book regarding wheels are based on many sources, not just one.
Has anyone actually done the opposite, and to deliberately send airflow into the wheelwell, and thus cool the brakes? I've had a mild idea that the wheel itself could be designed to work like a fan, with blades, to suck cool air into and over the brakes.
Brake ducts are common, and yes, wheels with fan blades have been used to cool the brakes.
That's so funny, I had this thought just today as well. I think the idea is to pull air from underneath the car and out through the wheel rather than push it in. This might be because there is a pressure differential between the high pressure floor area and the low pressure wheel well. As for the fans, I think thats what the 80s rally cars were doing with the turbofan wheels. Hi from Australia
Why do you think the undercar area is a high pressure? It usually isn't.
@@JulianEdgar You mentioned in another video that by lowering the floor under the engine bay you were able to generate a high pressure region and get a bit of a venturi effect. This is no doubt covered in your book ;) I haven't bought it yet but I subscribed to your channel as a reminder a while back.
Low pressure under the car with the undertray, not high pressure. Buy the book, measure stuff for yourself and then it will all become very clear.
Thought you might get a kick out of the moving front wheel spats on my RX7. It's primarily aesthetic, but also intended to reduce drag.
czcams.com/video/B-Mk5TCV0VQ/video.html
czcams.com/video/qbSDIWw-zxQ/video.html
Anyway, was just going through some of your videos thinking about making some type of front air dam to help increase pressure for the bottom feed radiator, and considering the trade off for increased drag. I intend to do a flat bottom and rear diffuser next, would hate to disrupt the under car flow too much. Better buy your book before that 😁
So sad about the Insight.
Would be nice to see car where whells give +30% drag. Actually, it is unbelevable. I expected to see prove.
In my book I cite multiple peer-reviewed technical papers and textbooks that show this to be the case.
@@JulianEdgar thank you
😂 People are rediscovering hubcaps. Hilarious.
Very few hubcaps in the past were used to reduce aero drag.
Yea but aero wheels are just way too ugly😢