Suspension Ideas and Questions

[C09]

Hi! Just signed up.

Would having one wishbone shorter than the other result in useful chamber as the suspension compresses? I think it would. As the body rolls, the upper wishbone moves a little over the lower one, affecting chamber. Say, a left turn, the body rotates rightward, and the right suspension compresses, the left lifts a little. (or a lot) The dual wishbones keep the tyre parallel to the body. in the turn, the outer contact patch of the tyre is pressed harder on the track than the iner side, and the opposite for the left tyre. Having a slightly shorter wishbone on the upper arm would likely improve chamber in turns, right? ( I wonder how fast someone will reply...)

[747heavy]

[Jersey Tom]

With an a-arm suspension, the tires will always camber away from the corner as the body goes into roll. At best the change will be close to 0 if you run a very short VSAL.

Unequal length in the A-arms just means your VSAL (parallelism) changes with travel.

[C09]

This diagram describes what happens with a bump, with no body roll. I know the body rolls very little in a turn, but it still rolls. This moves the top A-arm over the bottom one slightly, maybe half a milimeter, but this affects the contact patch. Also, as the car rolls, the outer wheel travels upward in it's suspension travel range, and a shorter arm would help keep chamber closer to optimum throughout the combined rollof the car and compression of the suspension.
(I might not be saying it right...)

[C09]

I'll emphasis that roll and suspension compression need to be combined for this to have a real advantage. and the effect it would make wouldn't be very much. not enough to compromise the chamber as the vehicle zooms at 200 kph and compresses the suspension. wouldn't want to ride on the inside edges of the tyre at that speed, would you? this would only alter the chamber to better handle corners a little bit. the only thing I can't figure out is which arm would have to be shorter? It would only be a centimeters difference or less on a f1 car, no?

[747heavy]

the left part of the graphic shows what happens if the suspension compresses (camber increases), as your outer wheel compresses in a turn, düe to roll, it should answer you question.
the inner wheel will do the opposite, as it extends during roll

But you have to keep in mind, that your outer tire will/would loose camber, due to body roll, the cambergain, will just make it less.
Depending from your suspension layout (camber gain), you will either loose less camber, keep it constant or even gain during roll, with your shorter top wishbone.

[C09]

Do F1 cars use slightly shorter arms today? How else do they maintain the correct camber in a turn?

I've observed that the tyres are actually slightly cone shaped. This obviously helps, but I only vaguely know how, other than it helps camber.

Also, could someone elaborate on how the angle of the steering axis changes handling? I've never figured it out.

P.S. I learned most of what I know from Forza Motorsport 3. It involves lots of trial and error tuning a Toyota Treuno. It was monotonous. The rest is from my own wits and watching a race or two. Soooo, I don't KNOW anything, just educated guesses. Please, educate me! I learn fast.

[Jersey Tom]

The tires aren't "cone shaped."

Also there's no such thing as "maintaining the correct camber." An "optimum" design that's perfect in every way is a load of BS. Everything is a compromise.

If you want to maintain a camber angle through a corner, run a solid axle.

What does the angle of the steering axis do - Either Kingpin or Caster angle. Either way it adds dynamic camber change with steering - which effects grip level at weight jacking.

You can run one arm shorter on the top, or on the bottom, or the same length.. whatever. It's whatever the engineer thinks is going to give him the performance compromise he deems best. The more springrate you throw at a car (for aero reasons for example) the less kinematics do for you anyway.

Hell while we're at it, the "right" amount of camber and blah blah blah is probably going to be different for hot tires at high inflation, than cold tires at low inflation, than used or new tires. You can't win it all.

Reading 'Tune to Win' is a good start on a lot of this stuff. It's taken 5-6 years of working with this in an engineering environment to wrap my head around most of it, and there's still heaps to learn.

[machin]

Hell while we're at it, the "right" amount of camber is probably going to be different for hot tires at high inflation, than cold tires at low inflation, than used or new tires. You can't win it all.

To add my 2p: ....and since having a shorter upper wishbone gives some (amount depends on the ratio of the lengths) camber recovery in roll, it means going over a bump (or when subjected to load transfer, e.g. during braking and acceleration) causes the tyre to gain camber (not good). An equal length set-up won't (in this instances that's a good thing)... so the "ideal" set-up also depends on whether we gain the most performance (i.e. lower lap time) from optimising for cornering, or optimising for bumps/load transfer, which depends on the track....

It also depends on other aspects of the car, such as the position of the CG and wheelbase or track and therefore whether load transfers are small or big (and whether they're bigger or smaller in longitudinal directions compared to transverse directions), or whether the car has lots of power (in which case we want to avoid the tyres standing on their inside edges on acceleration when the rear squats due to load transfer or we won't be able to transmit that power...).

The amount of anti-roll or anti-squat or anti-dive in the suspension geometry also has a bearing on whether we want camber recovery too...

... and the width of the tyres also has an effect on the decision since wide tyres don't like any camber gain compared to the ground plane....

As Tom says; "Tune to win" is good, or "Race and Rally Car source Book" is another good one.....

In answer to your question about F1 cars -I would expect that the upper wihbones are very slightly longer then the lowers to give some camber recovery in roll. Sometimes the geometries in F1 look really odd -in the quest to raise the nose say and gain better air-flow under that portion of the car, at a small expense to the geometry.... so taking too simplistic approach to observing what an F1 car has can get you in all sorts of a muddle!

[DaveW]

In answer to your question about F1 cars -I would expect that the upper wihbones are very slightly longer then the lowers to give some camber recovery in roll. Sometimes the geometries in F1 look really odd -in the quest to raise the nose say and gain better air-flow under that portion of the car, at a small expense to the geometry.... so taking too simplistic approach to observing what an F1 car has can get you in all sorts of a muddle!

..& you should definitely ignore the fact that there is sometimes an overlap of F1 & GP2 qualifying times on some circuits, despite agricultural aero, a weight penalty, control tyres, no tyre warmers & 150 hp less in the case of GP2.

[marcush.]

dave..speaks out ..the more you know ..well it is damn easy to get lost on the trip enough to be slower at the end...testemony of a lot of top teams got lost in the upgrade jungle instead of maximising of what they got and KNOW.
It must be a tough lesson to learn for all those boffins that NEW and more potential is not necessarily translating into lap time...

[747heavy]

How else do they maintain the correct camber in a turn?

O.K. keeping in mind what everybody else here said, let´s change the question to.
How else can we alter the camber in turn?

Appart from your proposed shorter wishbone/ A-arm, the inclination (angle) between the upper and lower wishbones will have a effect as well, and can be used to tune for the desired characteristic.

If you search for non-parallel link/wishbones and/or unequal length links/wishbones
you will find a lot of informations in the web.



maybe this is a start:
http://www.autozine.org/technical_schoo ... ling_2.htm

[Giblet]

747, I would like to say thanks for being one of the few true contributers of impartial technical knowledge on this forum, and a level head when people get pissy.

Seriously, we need more like you.

Tomba should put you on the payroll, or send you a cake or something

Cheers.

[humble sabot]

I find the premise of this conversation slightly odd.
I'll tell you why. As a rule the vast majority of cars with wishbone suspension have unequal lengths, and not only that i bet you'd have a bitch of a time trying to find one with longer wishbones on top (having the contact patch tuck under the car). I can't imagine a case where you'd actually want to add positive camber under roll or bump. In practice it comes out to a matter of degrees. The primary objective is to help to keep the tyre within its optimum camber range to maximise grip. F1 cars and some others often have a noticeable amount of negative camber at rest, especially on the front.

to respond to two other things:
I've noticed the same thing in f1, sometimes it looks very much like there is a real taper to the tyres, the outside sidewall being taller. I'm not certain if this is an optical illusion or the actual state of things. I'll try and find a pic.

and the other: f1 uses fairly the longest arms they can, the longer the arm the less change in angle.

[mep]

May I step into this discussion?

I can't imagine a case where you'd actually want to add positive camber under roll or bump.

When your car is cornering (roll) you must transmit a force trough your tires pointing towards the center of circle. Your tires transfer highest forces when they are slightly tilted. So your outside tire has negative chamber but your inside tire has the same characteristic. So you can also tilt them little bit to get highest grip. On the inside tire this results in a demand for positive chamber.