Rear wheels

[abide]

Hi all,

I have a technical question related to some well-known cars like Mercedes. Most of us have experienced on the road that the rear wheels of those cars are getting tilted as the speed of the car increases. I said tilted but I don't know exact term for the situation. I mean that the rear wheels are standing let say almost vertically when the car is stand still. However, as it speeds up, the vertical position of the wheels are changing towards the horizontal position. Okay not completely horizontal but some degrees. Most people in my environment believes that that it is a unique property of the Mercedes or some other famous cars. Can you comment on it? Is it true that the rear wheels are tilting sides as the speed increases?

Thank you.

[Jersey Tom]

No magic about it. The 'tilt' is known as camber. On many cars with independent suspensions, the wheels will gain negative camber as the suspension squats down.

A car with some downforce, as it speeds up the suspension will squat and the wheel will gain cambr.

[abide]

So you are saying that there is no difference between Mercedes rear wheel and any other car's rear wheel. Just a down-force caused by speed and camber relation.

[Tim.Wright]

Yea exactly what JT said. Though if this is a road car, I think what you are seeing is not due to downforce but "squat" of the rear axle under acceleration.

+1 that its not a unique Mercedes thing, but it is unique to independant rear suspension.

Google "camber gain" to find out why it is done.

Tim

[GSpeedR]

I'm guessing that the "Mercedes" that 'abide' is referring to is the non-production vehicle with active-camber control. As mentioned above, many passive suspensions will "gain" camber with travel, which is an important aspect of kinematic suspension design. Also, passive suspensions will experience camber changes due to suspension compliance, basically a change in wheel alignment due to non-rigid links.

An active system has the ability to control overall camber angle through some sort of actuation (hydraulic most likely), and can adjust camber beyond what is prescribed by the suspension kinematics and compliances. This is very rare and not found on any production vehicles.

[venomenon]

just an educated guess.

I imagine that the camber will reposition itself to zero or close to zero when the acceleration of the car is 0

[Dragonfly]

Depends on the factory design. Some cars may have a predefined static camber angle - positive or negative.

[she_spools_180]

Depends on the factory design. Some cars may have a predefined static camber angle - positive or negative.

hmm... all cars that I have worked with (admittedly not a large selection) have all had negative static camber angle. Are there production (or any other) cars that have positive static camber angle from the factory? It would seem counter productive to have this. If there are cars like this could someone please explain why this would be used? I see ONLY disadvantages to this...

[flynfrog]

Depends on the factory design. Some cars may have a predefined static camber angle - positive or negative.

hmm... all cars that I have worked with (admittedly not a large selection) have all had negative static camber angle. Are there production (or any other) cars that have positive static camber angle from the factory? It would seem counter productive to have this. If there are cars like this could someone please explain why this would be used? I see ONLY disadvantages to this...

I dont think any would choose to have positive camber maybe some weird trailing arm stuff. Some suspension designs end up with some positive camber. Look at some of the long travel suspensions used in desert racing. They will gain positive camber at full droop.

[she_spools_180]

Depends on the factory design. Some cars may have a predefined static camber angle - positive or negative.

hmm... all cars that I have worked with (admittedly not a large selection) have all had negative static camber angle. Are there production (or any other) cars that have positive static camber angle from the factory? It would seem counter productive to have this. If there are cars like this could someone please explain why this would be used? I see ONLY disadvantages to this...

I dont think any would choose to have positive camber maybe some weird trailing arm stuff. Some suspension designs end up with some positive camber. Look at some of the long travel suspensions used in desert racing. They will gain positive camber at full droop.

I do understand that when you have full droop, you will have positive camber but...
I did say static camber angle, which if I am not mistaken, should be angle when sitting under its own weight? So does this exist?

[flynfrog]

Not on production cars. I have seen Oval track cars try it on the left front. I cant recall any production car with positive camber.

[kalinka]

Can't find a picture to prove, but here in Serbia there's a (in)famous "car" called Zastava 101, that has postive static camber when the car is unloaded. I think the idea is that when the car is under load at rear (4 or 5 passangers + luggage), the suspension moves into negative camber position. It's a very ugly solution, I can tell you. The car looks very strange from behind...
The car is not in production anymore (thank god).

there it is > funny isn't it ?

[thisisatest]

early volkswagen rabbits (golf mk1 outside the us)specified positive static camber on the front wheels. probably with no power steering, it's much easier to turn the wheel, scrub radius is smaller.
i dont recall seeing intentional static positive camber on rear wheels.