Not sure how to ask the question: what are the physical differences and similarities between the two forces? How are F1 cars or any car affected by the two?

mick viper - 18 August 2008 09:17 AM

Not sure how to ask the question: what are the physical differences and similarities between the two forces? How are F1 cars or any car affected by the two?

Weight is a function of mass and gravity -- how much physical stuff you have.

Downforce is just what it sounds like -- the force of air being deflected and the resultant push it puts on the car in a vertical direction. More precisely, it is one of the two components of aerodynamic force, the other being drag, which holds the car back like a parachute.

Both forces push the tyres down onto the pavement, so what's the difference? Mass -- the amount of physical stuff you have. Mass is something you have to apply power to, to accellerate, decellerate, turn corners and so forth, the same way you feel resistance when you push a car or a pendulum.

If adding weight had no penalty, cars would be very, very heavy (or rather, massive) indeed. The problem is, it does have a penalty. As weight (mass) increases, you have to apply more force to accellerate it, you need stronger brakes to slow it, and more grip from your tyres to apply those forces. You also have to make everything else on the car stronger to resist them.

Downforce, on the other hand, is the "almost freebie" of increasing grip. As I said, it is the result of re-directing air by pushing it out of the way. It does not add mass, and therefore does not cause a "pendulum" effect as the car goes through corners. It doesn't require bigger brakes to stop, either. In fact, aerodynamic drag can, itself, act like a "brake." Some cars, notably the Mercedes 300SLRs that ran at LeMans in 1955, had "air brakes" in the form of a large section of bodywork that rose up like a convertible top to slow the car from full speed on the Mulsanne straight.

There are a few drawbacks, however; as I said, downforce is an "almost freebie."

One drawback is aerodynamic drag. Any time you interrupt or re-direct airflow, you cause drag. That slows the car. It also slows accelleration. Since drag increases as the cube of speed, if you double the car's speed, you add eight times the drag, so the faster you go, the more slowly you accellerate.

The other problem is that downforce is still a force. LIke weight (which is mass multiplied by gravity), it puts stress on the chassis, springs, suspension components and everything else. Thus, they have to be made stronger (and thus heavier) to resist the the downforce.

That adds its own set of problems: suspension breakage and the need for stiffer springs, among them. I'm not sure what spring rates today's cars use, but they're probably quite stiff; the tyres are the "spring medium" in a lot of cases. At the height of the "ground effects" era, cars ran springs of 900 pounds per inch of compression at the front and 1,200 pounds at the rear, 0r 4,200 pounts per inch. If a 150 pound driver stepped aboard a car that stiffly spring, the chassis would settle a little less than a millimeter.

The other drawback of aerodynamic downforce is that when the wings, diffuser, side pods or whatever stop working, downforce goes away in a BIG hurry. If the car gets sideways, or loses the flow of air over the wings, it stops having thousands of pounds of downforce and suddenly becomes a 1200 pound racer again. And the tyres lose grip. So, if you hang the tail of a car with a lot of mass out like a dirt track sprinter, you have to fight the "pendulum effect, but you still have weight on the tyres. When you lose downforce, you lose grip. The difference between "Oh, wow!" and "OH NO!" gets a lot thinner; you lose grip suddenly and can't get it back as easily.

The other factor is the Technical Regulations. As technology improved, meaning the cars are going faster, the FIA, restricts what they can do to go faster and handle better. So while the explanation of the physics of Downforce and Weight are good, in theory, they (the teams and cars) can, to a degree, manage and manipulate those forces to their will to get the car to do what they want, not the FIA. Weight and Downforce are factors, that is an absolute. But give a team a car that can be unrestricted, and see what happens.

I guess what I am trying to convey is, even though those are undeniable forces, an unrestricted F1 car, can almost null these points.

Crowbar,
Exactly which points Greywolf posted, would an unrestricted F1 car null?

I'm very interested in your theory about that.

grtz
Bob

speedy_bob - 20 August 2008 08:20 AM

Crowbar,
Exactly which points Greywolf posted, would an unrestricted F1 car null?

I'm very interested in your theory about that.

grtz
Bob

Not really.
To be "perfect," the car and driver would have to weigh zero pounds, with a mass of zero kilograms, have zero drag and generate infinite power and downforce. An "unrestricted" F1 car would still have to deal with mass, aerodynamic drag and the limits of its torque and horsepower. Enormous downforce -- particularly if it was independant of speed, as with the Brabham BT-46 or the Chaparral 2-J -- would help cornering speed and braking, but you still have to move the mass. The laws of physics still apply.

speedy_bob - 20 August 2008 08:20 AM

Crowbar,
Exactly which points Greywolf posted, would an unrestricted F1 car null?

I'm very interested in your theory about that.

grtz
Bob

O.k., I'll do my best. You are dead on correct, there will always be weight and downforce, but, what I mean is, if the car can be made unrestricted, you could for example have a movable rear wing, adjustable for faster and slower speeds. For weights sake, you can have an unrestricted engine, making the power to weight ratio more than 1:1, say like, 2:1, the weight almost wouldn't matter because you have the power to overcome the weight holding you back. And there are many more examples.

Crowbar - 20 August 2008 05:09 PM

speedy_bob - 20 August 2008 08:20 AM

Crowbar,
Exactly which points Greywolf posted, would an unrestricted F1 car null?

I'm very interested in your theory about that.

grtz
Bob

O.k., I'll do my best. You are dead on correct, there will always be weight and downforce, but, what I mean is, if the car can be made unrestricted, you could for example have a movable rear wing, adjustable for faster and slower speeds. For weights sake, you can have an unrestricted engine, making the power to weight ratio more than 1:1, say like, 2:1, the weight almost wouldn't matter because you have the power to overcome the weight holding you back. And there are many more examples.

Except the weight IS holding you back. It's going to be harder to slow down a heavier car, and it's going to be harder to corner in a heavier car. It's also going to take more fuel to propel the car, adding further to the weight. As Grewolf pointed out, this is precisely why it's preferable to have downforce than increased actual mass. That is, it's as if the "weight" only acts to pull you down towards the track without having to worry about pesky things like inertia.

Except the weight IS holding you back. It's going to be harder to slow down a heavier car, and it's going to be harder to corner in a heavier car. It's also going to take more fuel to propel the car, adding further to the weight. As Grewolf pointed out, this is precisely why it's preferable to have downforce than increased actual mass. That is, it's as if the "weight" only acts to pull you down towards the track without having to worry about pesky things like inertia.

I never mentioned anything about extra weight. An F1 car built unrestricted does not necessarily mean more weight. Unrestricted means using the best ideas, materials and tech available. I suppose I should have mentioned the only restriction would be the total weight of the car, and from there build your car according to a basic formula not a restricted one. Think about it and research past F1 R&D;. The FIA restricts these cars for a reason. You leave the engineers to design and build their cars without restrictions and they'll make that thing go to Mars!

Crowbar - 20 August 2008 09:36 PM

Except the weight IS holding you back. It's going to be harder to slow down a heavier car, and it's going to be harder to corner in a heavier car. It's also going to take more fuel to propel the car, adding further to the weight. As Grewolf pointed out, this is precisely why it's preferable to have downforce than increased actual mass. That is, it's as if the "weight" only acts to pull you down towards the track without having to worry about pesky things like inertia.

I never mentioned anything about extra weight. An F1 car built unrestricted does not necessarily mean more weight. Unrestricted means using the best ideas, materials and tech available. I suppose I should have mentioned the only restriction would be the total weight of the car, and from there build your car according to a basic formula not a restricted one. Think about it and research past F1 R&D;. The FIA restricts these cars for a reason. You leave the engineers to design and build their cars without restrictions and they'll make that thing go to Mars!

No, but you clearly said "the weight almost wouldn't matter because you have the power to overcome the weight holding you back.". That is the part I was addressing.

No, but you clearly said "the weight almost wouldn't matter because you have the power to overcome the weight holding you back.". That is the part I was addressing.

If the power to weight ratio of the car is 2:1, then no, the weight of the car is not an issue because you have power to overcome the weight of the car. To draw a parallel, a plane needs wings to fly, but in the case of the F-22 Raptor, it's power to weight ratio is more than 1:1, "...meaning in a vertical climb the wings are almost unnecessary." An official quote from the documentary.

Perhaps "...holding you back." wasn't the best way to put it.

Crowbar - 20 August 2008 10:14 PM

No, but you clearly said "the weight almost wouldn't matter because you have the power to overcome the weight holding you back.". That is the part I was addressing.

If the power to weight ratio of the car is 2:1, then no, the weight of the car is not an issue because you have power to overcome the weight of the car. To draw a parallel, a plane needs wings to fly, but in the case of the F-22 Raptor, it's power to weight ratio is more than 1:1, "...meaning in a vertical climb the wings are almost unnecessary." An official quote from the documentary.

Perhaps "...holding you back." wasn't the best way to put it.

And again, it's not just about building a car that can accelerate. It's about building a car that can accelerate and equally as important, brake and corner well. That is the whole point - you want a car as lightweight as possible to help in all three areas.