Front suspension geometry
 

Hello all!

Does anyone here have a clue what I´m talking if I say things like 'axle-pin rake' or 'nachlauf'?

What I need to know is how much of that it is good to have with mcperson-suspensioned front in Beetle? In other words: How much my wheel stub centerline must be offset (to front) from straight line drawn between lower ball-joint and mcperson upper-bearing?

How much positive caster is good for non-powersteered light front-end car like Beetle is?

Thanks!

I know what you are asking, but do not know the answer. I think you might want to post in the racing forum. I would also just find out from the Porsche guys what sort of angles they have and go from there. Bugformance did a Mac strut setup beetle and might have already figured out that answer.

Bugformance Build

I know what your talking about Tommi. The caster angle should be around 2 degrees positive. The upper strut bearings will be behind the spindles if you were to look strait down at the front hub.

*More negative caster may make the steering easier, but may also make it harder to find the steering's center while driving.

The car will pull towards the side with the least positive caster, and pull towards the side with the most positive camber. Caster angle doesn't generally adversely affect tire wear, but camber angle, and excessive toe in/out do.




-*edit;
after a cup of coffee this morning, I realized I made a mistake. Negative caster was what I meant to type. :o

thx Volkdent.

Thanks!

I´ve watched that oval-project, VERY nice but it´s just superbeetle suspension to oval beetle, nothing new if there is not some geometry changes etc...

Our race-splitwindow has McPherson front suspension (made with 914 and Passat parts) and it have 20 degrees of positive caster! Goes straight like a train!! :cool: And it also turns very good......

I agree with volkdent to find out what angles Porsche guys use.

I have also another question! :)

You have steering arms in your front spindle. Those arms are pointing either front or backwards. 'Big guys' say that steering arms pointing back you´ll have oversteer (which is good for light front car like beetle) and if you have steering arms to front you´ll have understeer. (which is good for naturally oversteering car like 944) So how it is possible that steering arm postitions can have effect to under-/oversteer of my car?!??!???? What makes this effect? :confused: :confused:

I don't get it myself. I asked about it before, but havn't heard what the difference is. My M3 has them towards the front, a bunch of other cars to the rear. Part of it may just be packaging, where the steering rack will fit and all that.

Jason

Answer for your and my question is Ackermann-steering.

But I´m not sure how it make the effect of oversteer or understeer... It is somehow related to angles how much front wheels are turned..... For example if you turn right all you´ve got your left front wheel turns let´s say 20 degrees and your right wheel 30 degrees. There is secret of that. BUT this will only happen (if I´m not completely wrong) when you have angled steering arms, not ones which are pointing straight front or back. (like 944´s are pointing straight front)

Cars which have straight (parallel) steering arms does not have Ackermann steering, because both wheels are turned same angles.

Then when you have angled steering arms, you can draw a line from lower ball-joint via steering-rod end so long that it will reach the car´s centerline. Then you draw same line from another side and then you look where does these lines cut. Is it front or back of the rear axle center or just at center of that. Then you´ll have 'More', 'Less' or 'True' Ackermann.

I don´t know how these make effect. I´ve found no information from the web and no one haven´t explain me this thing either.

For example 944 have parallel steering arms pointing front. 914 / 911 have angled steering arms pointing back. Why is that???

I think the placement of the steering arms on the spindles has to do with placement of components due to space available. Like Jason said, it's about packaging components together.

A 914 and 911 could feasibly mount it's steering aparatus either in front of, or behind the front wheel axis' because no other nessecary components occupy that area. Standard Beetles are "rear steered", or have steering arms, and steering aparatus behind the front wheel axis' as well, but only because the design warranted such an application. The steering box convieniently mounted on the upper torsion tube, and unequal length tie rods connected a common Pittman arm to rear facing steering arms. When designed, I think that Supers could have gone either way. I believe it could'ive been "rear steered" instead of "front steered" and the framehead would'nt look much different, but don't know if it would'ive made much difference in what was supposed to be such a humble, and conservative automobile.

On the subject of Ackerman angle. To find the corect angle for the steering arms, you draw a line throught the front ball joint to the center of the rear axle centerline. The tie rod should fall somewhere on that line. For front steer vehicle, just mirror the angle forward of the front axle centerline.

Hi

Something to be aware if your running excesive castor, the same forces that keep the steering wheel straight when going forward will work against you if you ever spin your car and find yourself going backwards fast, the steering will wip itself into a full lock condition.

Steve

I don't know where you heard that from tommi, but it's simply nonsense.
Either setup can be made to behave exactly the same in all respects.

But anyway, it's almost impossible to figure out all those angles in your head, and how they behave, during weight transfer for example, makes it even more complicated (there's too many variables involved).

These days you really need a computer program to do that properly - or feed the angles & information into a good simulator like Richard Burns Rally
Car manufacturers used to solve these issues just by trial and error up until around 1980, because it's a vey complex maths problem...