What are you talking about? I said you can add the 11 pounds and the 33 pounds together because if you figure each one separately it's going to equal the same net result in the end. I know for a fact it will because I figured them separately in the first place to make sure. I never said anything about lift in front, downforce in back. But just for reference the Nismo has downforce in both front and back while the standard Z has lift in both front and back. So your "thought" doesn't even apply here.

That statement right there tells me that you're guessing.

If you had any experience in this area this next quote of yours would have never been made..

LOL!!! Link to a real situation like this. This I gotta see.

That's why I got the formula from a vehicle aerodynamics website... But for the sake of the argument, provide a link or some real data to back up your "theory" instead of just making wild guesses.

 

I'll just give you a simple example.

Take a vehicle with zero lift aerodynamics front and rear.

No matter the speed, zero lift, correct?

Now add a spoiler in the rear to give the car downforce. We'll say at at speed, it gives the car 200 lbs downforce in the rear. What happens when you load the suspension with 200 lbs in the rear? The front lifts up. When the front lifts up, the front is now catching air, which is being compressed under the car, creating lift instead of downforce.

That 200 lbs measured downforce in the rear is actually more than 200 lbs, given that lift is also being created (e.g. the ACTUAL downforce created could be 300 from the spoiler itself, but creating 100 lbs of lift measured at the rear could result in a net 200 lbs).

This is still disregarding any front lift that may be created.

If this car were to go fast enough, the car would eventually get unstable enough to lose control.


Now lets go back to the Nismo Z. Rear lift is greater than the front right? Again, at a high rate of speed, the rear spoiler will create enough downforce that the suspension load will cause the rear to squat, and the front to lift. This is counteracted by the front downforce, but at some point, the front downforce will not be enough to keep the front planted. Fortunately, the Nismo Z should never be going speeds where that will become a factor.

I suggest you check out some SCCA forums, instead of just doing simple math.



Using your additive logic, if you double the horsepower of the engine, how much extra heat dissipation do you need?

 

http://www.longacreracing.com/articles/art.asp?ARTID=30

http://www.mcpmotorsport.com/The_Cars/TheCars.asp?ID=57

Why? because the front will begin to lift, even though the front itself creates downforce. The suspension squat in the rear pushes the front up, causing lift.

 

Yes that CAN happen. But even if it did, the downforce on the rear would still be greater than the lift on the front, so the car would technically still have a net downforce, not a lift. It would also depend completely on the suspension and the shape of the car.

But, for the sake of argument, just exactly how much lower does the Nismo rear end have to be in relation to the front end in order to reverse the downforce on the front end to lift? Is it even possible in the Nismo with stock suspension? I don't believe you can answer those questions.

You are arguing about a hypothetical situation which I'm certain is NOT an issue with the Nismo (the vehicle we are discussing in this thread). Maybe if we were talking about a Maxima with a ricer wing or something... but the Nismo was specifically designed and tested to keep itself planted at all speeds. End of debate.

 

Simple math.

Aerodynamic drag and downforce work in squares.

Spring rates work linearly.

For the sake of simplicity, lets keep everything 'ideal'. Double the speed, 4 times the downforce right?

11/33 at 74 were the figures stated above, so lets use those.

at 148, those figures would be 44/132.

Now, if you put 132 lbs of weight on the rear of the car at a dead stop, how much does the front rise? If you put 44 on the front, how much does the rear rise? Combine those, and if you put 132 on the rear, and 44 on the front, which side of the car has a net rise? Yes, the front! How much additional force is required to have the front have the SAME drop as the rear? That is the amount of lift generated in the front, just from suspension squat.

Now, lets triple the speeds.

99/297 @ 231. Now you can already see the front will have a significant rise from the downforce in the rear.

Now keep in mind, squat/rise will affect the actual downforce generated, and the Nismo has to go speeds far beyond what it will actually do (as I stated before) before this becomes an issue.

What it does add up to, however, is that downforce is NOT ADDITIVE on real cars, which was the whole point of this debate.
Yes, it is additive in theory. Real applications do not allow for it to be additive due to outside factors.

if an intake adds 10hp, and an exhaust adds 10 hp, and a reflash adds 20 hp, and headers add 10 hp, do they add 50 hp together? no.

 

To sum up, the equations are accurate in an ideal world.

In the real world, there are too many variables to simplify it into a simple equation.

Gross downforce can be calculated given ideal situations and no confounding variables. Net downforce must be measured with a windtunnel and scales.

 

Um... no.

Just because the front is a little higher in relation to the rear after forces are applied, that does not mean that there is lift there. The front may be higher in relation to the rear than it was at a standstill, but there is still downforce on the front as well meaning that there is more weight pushing down on the tires than there was at a standstill. The position of the front or rear because of forces acting on the car say nothing about the amount of force being applied to provide traction for the tires, which is what downforce is all about. 11 pounds pushing down on the front with 33 pushing down on the back means that the front is now higher than it was in relation to the rear at a standstill. So by your statement that means there's lift there which means less weight on the front tires... FAIL. Try again. 11 pounds of downforce on the front is still 11 pounds more weight.... otherwise it wouldn't be called downforce.

 

I provided the evidence you wanted, and you continue to ignore it.

There is no way around the fact that spring rates increase linearly, and downforce generated increases exponentially.

Double the speed, 4 times the drag. Triple the speed, 9 times the drag.

double the compression force on the spring, double the compression distance. Triple the compression force, triple the compression distance.

Simple physics 101.

 

Dude, you are trying to say that downforce is lift. So apparently it's not so simple for you. The opposite of downforce is called lift. If the Nismo had lift on the front at 73 mph it would say lift, not downforce. Get a clue...

 

Maybe you guys should go sit down and have some coffee.

 

I'm done with this thread anyway. I don't own a Nismo and I never will. I don't even like the Nismo to be honest, so I can guarantee my opinion is not biased towards it. If this guy wants to believe that cars are like teeter-totters and that by adding weight to the back you will take weight of the front, more power to him. I have better things to do. Enjoy.

 

I don't think you're understanding neither what I'm saying nor the physics behind it.

Downforce causes squat.

Double speed = quad downforce = 4x the squat.

Triple speed = 9x downforce = 9x the squat

The faster you go, the more you squat.

Yes, the applies to the front too, but the front is making less downforce. As you go faster and faster, the downforce disparity between the front and rear gets larger. Eventually, when you're going fast enough, the front downforce will not be able to overcome the lift from the squat caused by the downforce in the rear.

 

Perhaps you should take your Z to the track, which is what it is meant for, instead of the drag strip.

You'd do much better getting a G8 at the drag strip for less money.

Shall we go back on topic?

 

"Eventually, when you're going fast enough, the front down force will not be able to overcome the lift from the squat caused by the down force in the rear."

How can you be so sure? Have you actually tested this theory or read somewhere that Nissan tested the Nismo and said that once going at speed (x) the car will begin to fly! I would think this would be a warning somewhere if it was the case, don't you? Also, the way the down force is distributed to the front and rear of the car was decided resulting from lot of research and is balanced in such a way that the car will stayed glued to the ground not lift of the ground at higher speeds. If your theory was true then all the cars at Le Mans and the Drag Strip would always fly, keep in mind we are talking about speeds that are possible with street cars below 250MPH, I don't think anybody is arguing that if the car was traveling at 500MPH it might not be safe to drive or that it might lift, but who knows maybe it wouldn't lift only the engineers at Nissan and Autech know, they did the research.

Just my 2 cents.

 

Let's just say mine has seen 160 and it felt extremely planted at that speed with very tight steering. WAY more stable at that speed than a normal Z was at 120.

 

Why are you guys listening this guy? he does not even own NISMO 350z.

This guy is only right about what he stated but wrong on how NISMO 350z is setup.

The NISMO Autech Built car only puts down 37lbs of downforce.

NOT OVER 100..

Autech would have not built the NISMO 350z with body they did if it did not work.

 

+1. Well said.

It's a collectors cars. It does not have to justify itself, as long as it has Nismo written all over it, the car is badass.

 

Only 37lb at 70 mph. It gets much higher the faster you go, so it could be 200lb +.

 

^^Absolutely correct.


"only 37 at 70mph" is a lot, considering most cars at that speed already have a significant amount of lift at 70.

Zero lift in itself is a significant achievement.

I'll use the Infinitis as an example. They're all engineered for zero front lift for a specific reason. If the rear lifts slightly at high speed (100+), while the front has no left, it still puts more weight on the front, to maintain steering control at speed.

You do NOT want a floaty steering wheel when you're going fast

 

thank god.... i was really getting sick of you anyways. like i said earlier, i have a nismo, so it is better. n-uff said. mr. know it all