Rear Wings on FF cars

[byegad]

BTCC, that's British Touring Cars Championship, cars are almost all front wheel drive. Only the BMW and Toyota entries are rear wheel drive. All of the cars have rear wings, and the FF, in GT5ese, cars use the wing to gain rear grip and so a better balance in high speed corners. The FF cars win by far the most races.

 

[niky]

The FF cars win because of meticulous rules-tweaking that handicaps the FR cars so that they're just as fast as the FF entries. Given the same weights and power, the FR cars would be faster.

The Bernoulli principle does have an effect, but not large enough to generate lift by itself.

The lift on an aircraft's wing is generated by the appropriate angle of attack. Which is why aircraft can fly upside down. And why high downforce cars can fly right-side up given the proper angle of attack.

An underbody diffuser is an excellent example of the Bernoulli Principle, though. And perhaps I spoke in haste. Spoilers that alter the shape of the car also primarily utilize the Bernoulli principle. While wings may be shaped with it in mind, many are there simply to push the car down by redirecting airflow. Which is why they're mounted as far off the body of the car as possible. Hence the comical laundry hamper wings.

 

[Exorcet]

If I'm not mistaken, the spoilers on the tops of airplane wings are "brakes". Flaps that pop up to disrupt airflow and increase drag slowing down the mass. Fighter jets have similar ones usually toward the rear of the plane. This also helps their stability.

Spoilers do create drag, but that's more of a secondary function. Most fighters don't have spoilers, they have airbrakes, though the two cam be pretty similar. The primary function of a spoiler on a plane is to reduce lift. This prevents the plane from going aeroborn again just after landing and increases tire traction (more grip from downforce) to aid braking.

Something that helps me understand this better is 2 examples. Top fuel dragsters have a wing. Until they get past a few hundred feet and actually generate speed, they don't do a whole lot in terms of downforce. Once they hit that sweet spot and the clutch hits full lock, the downforce can be measured in tons.

Aero force grows with velocity^2 (roughly). There isn't really a sweet spot, it just gets bigger constantly.

Which brings me to my other example. F1 cars also have wings. Now the rear wing may be for downforce, forgive my ignorance if it's not, but if IIRC the front wing doesn't. It creates a vacuum under the car by manipulating the airflow. The last F1 race I watched on TV (India), David Hobbs made the statement if an F1 car can maintain speed it is theoretically possible to drive on the ceiling. Please correct me if I'm wrong because I'm intrigued by the concept as well and seek pertinent, viable and correct information to better educate myself.

The front and rear wings on a F1 car do exactly the same thing. The front wings just operate in ground effect, which means close proximity to the moving ground enhances the bernoulli effect and weakens tip vortices. This makes the front wing more efficient than the rear.

The Bernoulli principle does have an effect, but not large enough to generate lift by itself.

That's the thing, there isn't really any by itself. Bernoulli, Momentum exchange, pressure differentials, and circulation are really all the same thing. Once you have on, you have the others.

Flow through a pipe with expanding area does not have constant momentum. At the narrow end of the pipe, the momentum (rho*v*v*Area_cross_section) is 1 (let's say). At the wide end it's less than that. You can find the new momentum using mass conservation (m_dot = rho*v*A) which also gives you the new v and hence pressure from bernoulli. The missing momentum was actually transferred to the walls of the pipe and is seen as a force.

The lift on an aircraft's wing is generated by the appropriate angle of attack. Which is why aircraft can fly upside down. And why high downforce cars can fly right-side up given the proper angle of attack.

AoA doesn't really generate lift, it's more of a parameter. Wings at 0 or negative AoA still generate lift, how much lift they generate and the zero lift AoA depend on the airfoil.

 

[generationlost]

Bernoulli be damned, a wing doesn't produce downforce because of air speed or pressure differential. Otherwise the humped shape of the car would practically guarantee flight.

Instead, wings and spoilers generate downforce by pushing air flow up, which generates the simple Newtonian reaction of pushing the car down.

Even a completely flat wing works as long as the angle of attack is correct. Some wings just happen to be curved to collect more air at the expense of a massive increase in drag. That angle of attack is why racing cars sometimes do spectacular flips when the front wheels go up, as the aero hits the right angle of attack to launch the car into the air.

Turn a car upside down and I can guarantee you the reverse airfoli shape would generate more lift than downforce.

That's a common misconception. If wings worked that way, there would be too much drag. In fact the "humped shape" of cars often do produce lift at high speeds. That's why we add aero bits on to the car to keep it on the ground.

http://www.compositesworld.com/articles/composite-wing-key-to-high-speed-stability

Here's a link that shows that CFD images of the airflow around a Dodge Viper ACR. It's well known that this car produces a lot of downforce from that massive wing. As you can see, the airflow speeds up and goes underneath the wing which pushes that car down. There's even a diagram of a cross section of the wing, and it's shape is clearly not meant to have air "push" on the wing. It very much resembles an upside down airfoil.

Edit: Also, race cars flipping is due to high pressure air getting underneath the car and not so much due to air pushing down at the back of a car. I think I'll step aside and let Exorcet do any further explanations on this topic. He seems to have a deeper understanding of the nature of aerodynamics/fluid dynamics than I do.

 

[generationlost]

https://www.youtube.com/watch?v=g8XxQkXCmsU

Here we have the car catching air underneath the underbody, creating a high pressure zone and ultimately leading to the car flipping. Correct me if I'm wrong, but since it was drafting the car in front of it, it wasn't producing any front end downforce and as it went over the crest of the track, the front end lifted from the ground, catching air underneath it.

 

[Argon]

https://www.youtube.com/watch?v=g8XxQkXCmsU

Here we have the car catching air underneath the underbody, creating a high pressure zone and ultimately leading to the car flipping. Correct me if I'm wrong, but since it was drafting the car in front of it, it wasn't producing any front end downforce and as it went over the crest of the track, the front end lifted from the ground, catching air underneath it.

I don't think that statement is wholly correct. The example you have given is one that demonstrates the cross over between Bernoulli's effect and Newtons law. The car most definitely was producing downforce at the time it started to lift however it's energy was sufficient to overcome that downforce. What happened once it had broken it's downforce tether was that Newtons law kicked in on the exposed underside of the car i.e. lift force is equal to amount of deflection in the flow.

I would agree however that the aerodynamic properties at the time the car broke its tether to the road were severely disrupted by the lead car and the pressure within the flow over the aero surfaces would have been altered.

 

[Exorcet]

Here's a link that shows that CFD images of the airflow around a Dodge Viper ACR. It's well known that this car produces a lot of downforce from that massive wing. As you can see, the airflow speeds up and goes underneath the wing which pushes that car down. There's even a diagram of a cross section of the wing, and it's shape is clearly not meant to have air "push" on the wing. It very much resembles an upside down airfoil.

The high speed air underneath is a result of Bernoulli, and it goes hand in hand with pressure and force.

However the wing does push on the air. If we ignored the car for simplicity, air ahead of the wing would be traveling parallel to the ground. Behind the wing, it would be angled up. This actually allows to measure the force on the wing. Prior to interacting with the wing, the vertical momentum is zero. Afterwards, it's positive and you can measure the quantity use density and velocity. Since the air has positive momentum, the wing must now have now have negative momentum since the initial vertical momentum all the way upstream was zero. This momentum exchange generates the downforce.

Edit: Also, race cars flipping is due to high pressure air getting underneath the car and not so much due to air pushing down at the back of a car. I think I'll step aside and let Exorcet do any further explanations on this topic. He seems to have a deeper understanding of the nature of aerodynamics/fluid dynamics than I do.

You're correct about the high pressure underneath, but the top surface plays just as much as a role. Cars typically produce low pressure on their upper surfaces as a result of Bernoulli. Given the right AoA, as niky said, they'll generate enough lift to take off.

The car most definitely was producing downforce at the time it started to lift however it's energy was sufficient to overcome that downforce.

Most likely, the initial cause for the flip was pitching moment and not lift. The car had an unstable positive pitching moment, so even if it was produce 200000 tons of downforce, it was still going to flip. Whether or not the front end was producing downforce, the balance between front and rear was insufficient to keep the nose on the ground. This resulted in the nose lifting, even though overall, the car may have still been producing downforce. As the AoA went up, downforce was reduced until it became lift, and when the lift just began to exceed the weight of the car, it took off.

 

[snowgt]

Bernoulli be damned, a wing doesn't produce downforce because of air speed or pressure differential. Otherwise the humped shape of the car would practically guarantee flight.

Instead, wings and spoilers generate downforce by pushing air flow up, which generates the simple Newtonian reaction of pushing the car down.

I would say both is the case. The air passing underneath the wing is accelerated, produces a low pressure zone, and therefore also pulls the wing (and therefore the car) down. The effect of this depends on the cross-section of the wing. It is literally like an upside-down aircraft wing.

The shape of the car does not produce lift as much, because the underside of a car is usually flat and not curved like the car's body. The lift it does create is being remedied in higher powered cars with a diffusor, which uses the same principle, i.e. accelerating the air over the diffusor upwards and thereby creating downforce. The diffusor is basically just like the bottom part of a wing and it demonstrates quite clearly how the underside of a wing produces downforce (without the air pressing down on it from above).

 

[eight6er]

Yes of course rear downforce can help FF cars.
I saw this question come up a few times and it really amazes me how many people think it only helps RWD cars.

 

[generationlost]

I must say, this is a very enlightening and informative thread.

 

[Argon]

^^ I agree 👍

 

[Furinkazen]

I am not the biggest expert in this, but I would say that a wing would surely help no matter what? Weather for example its a BTCC Honda Civic (FF) or a BMW 320si (FR), the same basic rules apply that when your going forward your vehicle going through the air, and that a wing stabilizes the rear of the car. It pushes the whole car down.

In an FF (which naturally would understeer due to the front heavy layout or front engine and front wheels driving), the wing might make the understeer worse. If the point of it is to keep the car on the ground and stabilize the rear of the car, then that "tightening up" effect of the rear of the car will make the whole car harder to steer, increasing understeer as a result? That's why (as mentioned earlier) an FR would naturally be slower, the drive and weight transfer from the rear wheels would make it handle better, even if it had the same wing.

Correct me if i'm wrong but i've watched racing for around 8 years now and i'm pretty sure thats how things work.

 

[pixel_geist]

in FF cars I think the wing would help the most in deceleration, when the car's weight is shifted foward, onto the motor/ FWD. The wing created drag on the rear, pushing the rear end down. RWD cars have LSD torque in the rear end to help plant the rear, FWD's dont...

 

[eran0004]

The size of the rear wing makes us think that it produces a lot of downforce, but the reality is that the rear wing needs to be huge to be effective, because the airflow is disturbed when it reaches the rear. A front wing (like on F1 cars) can be much smaller because the airflow is undisturbed, so a smaller surface is required to be effective.

The reason why FWD cars have huge rear wings is thus because the rear wing needs to be huge on all cars to be effective, and FWD cars has just as much reason as RWD cars to stay on the ground.

 

[pixel_geist]

The size of the rear wing makes us think that it produces a lot of downforce, but the reality is that the rear wing needs to be huge to be effective, because the airflow is disturbed when it reaches the rear. A front wing (like on F1 cars) can be much smaller because the airflow is undisturbed, so a smaller surface is required to be effective.

The reason why FWD cars have huge rear wings is thus because the rear wing needs to be huge on all cars to be effective, and FWD cars has just as much reason as RWD cars to stay on the ground.

that plus the wing size is related to the speed at which it will be effective. Large wings are good when cornering, when speed is at a minimum. Take the Pikes Peak hill climb for example. The wings used in that event are monsters.

 

[Johnnypenso]

I am not the biggest expert in this, but I would say that a wing would surely help no matter what? Weather for example its a BTCC Honda Civic (FF) or a BMW 320si (FR), the same basic rules apply that when your going forward your vehicle going through the air, and that a wing stabilizes the rear of the car. It pushes the whole car down.

In an FF (which naturally would understeer due to the front heavy layout or front engine and front wheels driving), the wing might make the understeer worse. If the point of it is to keep the car on the ground and stabilize the rear of the car, then that "tightening up" effect of the rear of the car will make the whole car harder to steer, increasing understeer as a result? That's why (as mentioned earlier) an FR would naturally be slower, the drive and weight transfer from the rear wheels would make it handle better, even if it had the same wing.

Correct me if i'm wrong but i've watched racing for around 8 years now and i'm pretty sure thats how things work.

Depends on if we're talking about real life or GT5 and whether you're working up against a PP limit or it's wide open. In GT5 the problem with FF's is getting the rear to break loose, not grip more as a wing would do. And if you have to trade off HP to get the wing because you're up against a PP limit, I've never found a situation where a car was faster with a rear wing only, even FR's and MR's

 

[esoxhntr]

Depends on if we're talking about real life or GT5 and whether you're working up against a PP limit or it's wide open. In GT5 the problem with FF's is getting the rear to break loose, not grip more as a wing would do. And if you have to trade off HP to get the wing because you're up against a PP limit, I've never found a situation where a car was faster with a rear wing only, even FR's and MR's

One could argue the RR RUFs are easier to drive (and thus produce faster laptimes in the hands of most) with a rear wing. I still prefer them and am faster without one though.

Overall, I agree. Particularly in a PP limited room, wings are for feminine hygiene products.

 

[Connoissuer]

I feel stupid trying to understand all of this wing and spoiler ****. So far, all I've assumed is that a ZR1 has a spoiler and an ACR has a wing. No?

 

[Exorcet]

I am not the biggest expert in this, but I would say that a wing would surely help no matter what? Weather for example its a BTCC Honda Civic (FF) or a BMW 320si (FR), the same basic rules apply that when your going forward your vehicle going through the air, and that a wing stabilizes the rear of the car. It pushes the whole car down.

Pretty much. All fours tires contribute to cornering.

In an FF (which naturally would understeer due to the front heavy layout or front engine and front wheels driving), the wing might make the understeer worse. If the point of it is to keep the car on the ground and stabilize the rear of the car, then that "tightening up" effect of the rear of the car will make the whole car harder to steer, increasing understeer as a result? That's why (as mentioned earlier) an FR would naturally be slower, the drive and weight transfer from the rear wheels would make it handle better, even if it had the same wing.

Two things; FF doesn't only understeer. They can oversteer, massively. Lift off oversteer is a big problem for FF because if the weight transfer to the front is severe enough, the rear tires basically have no traction, and they aren't alligned perfectly straight with the direction the car is going, they'll slide around until they end where they shouldn't be, which sometimes results in the front wheels being ahead of the rears. A rear wing will make it harder to lose grip on the rear end.

Secondly, if you put downforce at the rear, you can also put some at the front to maintain whatever balance you want. Usually you want a specific balance that is best for your car, so if you add x amount of downforce in the front/rear, you need to add y on the opposite end to keep the car driveable. If you want max downforce, a rear wing is necessary, even on a FF car.

in FF cars I think the wing would help the most in deceleration, when the car's weight is shifted foward, onto the motor/ FWD. The wing created drag on the rear, pushing the rear end down. RWD cars have LSD torque in the rear end to help plant the rear, FWD's dont...

Drag from a fixed wing doesn't help the braking as much as the added downforce does. It's the extra tire grip that lowers braking distance. More importantly though, FF cars benefit from downforce like all other cars do. Acceleration, cornering, and braking can all be enhanced. The latter two are where the rear wing plays a role.

The size of the rear wing makes us think that it produces a lot of downforce, but the reality is that the rear wing needs to be huge to be effective, because the airflow is disturbed when it reaches the rear. A front wing (like on F1 cars) can be much smaller because the airflow is undisturbed, so a smaller surface is required to be effective.

This isn't always true. Front wings are usually more efficient because of ground effect. As for the rear wing, they don't have to be very high up or very large to get clean air. When you factor in the Coanda effect, even moderately large portions of "disturbed" air can interact with the wing without totally disabling its ability to produce downforce.

This images shows the velocity of the air down the center of the car. The air is laminar, or clean, everywhere except for two places; the wake behind the car and the boundary layer, which is the thin layer of air just above the surface of the car (it's colored blue/green). You can see that the wing can be fairly low without being stalled by bad air off the car. Size only matters in determining how much lift/drag you're going to make.

that plus the wing size is related to the speed at which it will be effective. Large wings are good when cornering, when speed is at a minimum. Take the Pikes Peak hill climb for example. The wings used in that event are monsters.

You're right that the larger the wing, the earlier a car of a certain size will feel its effect. Large wings aren't better at cornering though. LMP's corner as much as Hill climb cars do, but they have smaller wings. Despite the smaller wing size, LMP's make as much downforce, or more downforce, over the course of the race than the hill climb cars do. It's because they typically drive at high speed. If you mounted massive wings on LMP's, their top speeds would plummet to numbers you could reach with a modestly powerful family car. Finding the right wing size for a given application is a challenge, and it's one of the time consuming parts of aero engineering.

 

[MrWednesday]

And if you have to trade off HP to get the wing because you're up against a PP limit, I've never found a situation where a car was faster with a rear wing only, even FR's and MR's

Lotus Evora needs the downforce on some tracks depending on tune. I ran a lightened Evora in the British lightweights seasonal, and I had a lot of trouble with loss of control on Trial Mountain until I put a wing on it. It was much more stable with a little rear downforce.

 

[generationlost]

After all this stuff about spoilers and wings, I think I'll bring it back to the original topic and give the short answer to the OP. Yes, a rear wing will benefit an FF car, but you'll also probably want a front wing/splitter in order to keep the car balanced, as Exorcet said, and generate downforce over the front wheels as well.

In fact, an FF car would probably get more out of a front wing/splitter since it needs to keep weight over the front wheels. However, this increased grip at the front will now make the car more prone to oversteer. This is where the rear wing comes in: By adding a rear wing, the oversteer can be remedied by giving the rear tires more grip. The key idea here is balance.

I think this forum needs a "Technical section" where we can just discuss car stuff in general.

 

[niky]

Well, there is a "Cars in General" section.

The Coanda effect is still something I'm trying to wrap my head around, even after an entire season of F1.

-

RE: PP limits. Wings may or may not be effective in PP-limited rooms simply due to the way GT5 calculates PP. This is not to say that wings are ineffective per se in GT5, just that the specific handicapping applied to wings makes them less useful than, say, more power or less weight.

 

[Johnnypenso]

One could argue the RR RUFs are easier to drive (and thus produce faster laptimes in the hands of most) with a rear wing. I still prefer them and am faster without one though.

Overall, I agree. Particularly in a PP limited room, wings are for feminine hygiene products.

My RUFS are tuned without wings. I haven't tackled the Yellowbird yet with any seriousness, but the BTR and RGT are wingless for me. RGT has more relative grip and relative speed, but the BTR is still in the mix against most cars. Agreed on the feminine hygeine products...lol If there were no PP limitations and tuning was wide open, I'd probably have a wing on the BTR and Yellowbird.

Lotus Evora needs the downforce on some tracks depending on tune. I ran a lightened Evora in the British lightweights seasonal, and I had a lot of trouble with loss of control on Trial Mountain until I put a wing on it. It was much more stable with a little rear downforce.

If it's tuned properly it doesn't need a wing. If it's otherwise stock or improperly tuned you might need a wing, but with suspension and maybe ballast adjustments and no wing, it's a grip monster.

 

[McClarenDesign]

The Coanda effect is still something I'm trying to wrap my head around, even after an entire season of F1.

Maybe this will help.

 

[Jaywalker]

Yes of course rear downforce can help FF cars.
I saw this question come up a few times and it really amazes me how many people think it only helps RWD cars.

Yep. If you have a FF car with a loose rear-end, then a downforce-producing wing will help, at the expense of extra weight & drag, of course.

 

[Johnnypenso]

After all this stuff about spoilers and wings, I think I'll bring it back to the original topic and give the short answer to the OP. Yes, a rear wing will benefit an FF car, but you'll also probably want a front wing/splitter in order to keep the car balanced, as Exorcet said, and generate downforce over the front wheels as well.

In fact, an FF car would probably get more out of a front wing/splitter since it needs to keep weight over the front wheels. However, this increased grip at the front will now make the car more prone to oversteer. This is where the rear wing comes in: By adding a rear wing, the oversteer can be remedied by giving the rear tires more grip. The key idea here is balance.

I think this forum needs a "Technical section" where we can just discuss car stuff in general.

Other than on a handful of supercars, front wings and splitters are entirely cosmetic in GT5. Rear wings only add rear grip, something FF's do not suffer from a lack of which is why they don't need a wing in GT5.

Yep. If you have a FF car with a loose rear-end, then a downforce-producing wing will help, at the expense of extra weight & drag, of course.

When you find that extremely loose FF that can only be controlled with a wing, please let us know. I haven't found it yet in two years.

 

[Morgoth_666]

Other than on a handful of supercars, front wings and splitters are entirely cosmetic in GT5. Rear wings only add rear grip, something FF's do not suffer from a lack of which is why they don't need a wing in GT5.

That's news to me. I wasn't aware that there was even a single car where any aero parts other than the rear wing made any difference at all. All the cars I've seen have exactly the same numbers no matter what other parts you put on. I've never noticed any "hidden" effect on track either. Not saying you're wrong as I haven't checked everything(particularly on-track performance), but do you know of any examples? This has been a minor preoccupation and irritation of mine for a long time, is why I'm asking.

 

[Editor GEAR]

In the realm of GT5: My CRX has a spoiler and it actually has helped out with a serious under-steer problem it used to have. I find it a bit paradoxical that a spoiler helped an FF car with under-steer, but it did the job.

 

[esoxhntr]

That's news to me. I wasn't aware that there was even a single car where any aero parts other than the rear wing made any difference at all. All the cars I've seen have exactly the same numbers no matter what other parts you put on. I've never noticed any "hidden" effect on track either. Not saying you're wrong as I haven't checked everything(particularly on-track performance), but do you know of any examples? This has been a minor preoccupation and irritation of mine for a long time, is why I'm asking.

Ferrari California for one, comes with adjustable (or maybe its fixed, I can't recall) front aero.

 

[Ridox2JZGTE]

When you find that extremely loose FF that can only be controlled with a wing, please let us know. I haven't found it yet in two years.

You can try my Civic RM currently shared on my account, it has rear wing at low value, bring it to Spa, try to go flat out at Eau Rouge, it should do it, but if there's slight any mistakes, prepare for some rear tail action. The car does have oversteer, especially during aggressive trail braking. Of course it's not the car natural traits, it's just how it's tuned