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rainierdeklark Mon Apr 21, 2008 12:00 pm

Do I need to mount caster shims on my front beam when I lower my 1974 torsion Beetle as much in the front as in the rear (2 inches); the car stays levelled?

Hakka Mon Apr 21, 2008 1:09 pm

If the car is as level as stock then you will not need shims.

drscope Mon Apr 21, 2008 5:25 pm

YES! Caster shims will help the ride of the car when it is lowered from stock height regardless of what you have done in the rear.

You need to understand what caster is and what it does.

On your car, Caster is the imaginary line that goes through the center of the top ball joint down through the center of the lower ball joint.

The lower ball joint must be forward of the top ball joint. The angle of this imaginary line is how the caster is measured.

Caster is what makes the steering wheel come back to straight when you let go of the wheel when turning. It also helps the car to track straight and not wander all over the road.

The greater the caster angle, the faster and easier the wheel comes back to straight and the controlled and accurate the ride feels. Too much caster and it takes more muscle to turn the steering wheel because you are in effect lifting the front of the car when the wheels are turned because of the caster angle.

Caster is changed when dropping the front of the car simply by the rake of the car. If you lower the front, but leave the rear at stock ride height, you have moved the top ball joint forward, bringing that imaginary line closer to 90 degrees with the pavement.

But lowering the rear of the car will not fully correct the loss of caster. There is also a small caster loss simply because of the geometry of the control arms. When you lower your beam, you are in effect raising the control arms, simulating suspension compression.

This also changes the amount of caster.

I would recommend installing a set of caster shims when you do your beam. The only problem with having more caster then you need is the increase in steering effort needed to turn the car. And with a beetle, the front of the car is light enough that this should never be an issue.

They will help the car feel much more stable. And a set of shims is only about $10.

rainierdeklark Tue Apr 22, 2008 3:29 am

Thanks for the info.
Why I asked this question, was because I didn't know if the caster of a Beetle changes when the front wheel suspends. Maybe some cars do, it depends I guess on the construction of the front suspension.
So, would it be good to mount one set of caster shims to the LOWER beam, so that the beam tilts more backwards?

Hakka Tue Apr 22, 2008 7:36 am

drscope wrote: YES!

Thank you for setting me straight
I did not take into account for the articulation of the arms

rainierdeklark Tue Apr 22, 2008 9:53 am

So if you're driving down from a steep hill, your Beetle would steer really crappy (less or no caster)..... ;)

hemifalcon Tue Apr 22, 2008 10:02 am

why would driving down a steep hill change anything?? Your car is level with regards to the location of the front and rear suspension. The front arms do articulate, you have to look at each arm as being a pendulum, and they swing at identical arcs, but on diferent planes. Seeing as they are connected by the knuckle, that knuckle moves dependent on their locations in each respective arc. The caster shims will help to correct the new geometry back to the original geometry if the car has been lowered and the arms are more horizontal than at stock ride height. It's not a perfect science, but I'm sure it could be stated better. I know that I've heard of people putting as many as 2 sets of shims in behind their lower beam housing.

Max Welton Tue Apr 22, 2008 10:26 am

SprÝ Norsk wrote: drscope wrote: YES!

Thank you for setting me straight
I did not take into account for the articulation of the arms
I think this is not a factor if drop-spindles are the means of lowering the front. In that case the trailing arms are at the same angle as stock.

Max

rainierdeklark Tue Apr 22, 2008 10:27 am

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rainierdeklark Tue Apr 22, 2008 10:28 am

hemifalcon wrote: why would driving down a steep hill change anything?? Your car is level with regards to the location of the front and rear suspension. The front arms do articulate, you have to look at each arm as being a pendulum, and they swing at identical arcs, but on diferent planes. Seeing as they are connected by the knuckle, that knuckle moves dependent on their locations in each respective arc. The caster shims will help to correct the new geometry back to the original geometry if the car has been lowered and the arms are more horizontal than at stock ride height. It's not a perfect science, but I'm sure it could be stated better. I know that I've heard of people putting as many as 2 sets of shims in behind their lower beam housing.

I don't think that's true to be honost
Caster is the angle between the pivot line and the vertical, meaning the perpendicular line.
And that angle definitly changes when you're driving on a slope.
Driving down from a hill is like you lifted the rear suspension.

Euphonic Tue Apr 22, 2008 12:32 pm

Hey guys. Can anyone link me or tell me where i can find a set of these shims. I plan on dropping the front of my car practically to the ground and i want to make sure that sterring is still safe. Also, are there any threads that have install instructions with pics? Thanks.

fatalifeaten Tue Apr 22, 2008 1:15 pm

Euphonic wrote: Hey guys. Can anyone link me or tell me where i can find a set of these shims. I plan on dropping the front of my car practically to the ground and i want to make sure that sterring is still safe. Also, are there any threads that have install instructions with pics? Thanks.

Checkum stickies. Link pin lowering in this forum, bajjoint in the late model forum. TONS of useful info.

hemifalcon Tue Apr 22, 2008 1:48 pm

I'm no physicist. But when you are driving down a hill, does your car really sit higher in the back than the front?? Think about it. Only when you jam on the brakes does your rearend lift higher due to force on a downhill than it does on level ground. I don't think it's much of an example. Just put some shims in there..


[quote="rainierdeklark"][quote="hemifalcon"]why would driving down a steep hill change anything?? Your car is level with regards to the location of the front and rear suspension. The front arms do articulate, you have to look at each arm as being a pendulum, and they swing at identical arcs, but on diferent planes. Seeing as they are connected by the knuckle, that knuckle moves dependent on their locations in each respective arc. The caster shims will help to correct the new geometry back to the original geometry if the car has been lowered and the arms are more horizontal than at stock ride height. It's not a perfect science, but I'm sure it could be stated better. I know that I've heard of people putting as many as 2 sets of shims in behind their lower beam housing.[/quote]

I don't think that's true to be honost
Caster is the angle between the pivot line and the vertical, meaning 90 degrees from the plane you driving on.
And that definitly changes when you're driving on a slope.
Driving down from a hill is like you lifted the rear suspension.[/quote]

rainierdeklark Tue Apr 22, 2008 2:54 pm

The whole principle of caster is based on gravity, which is straight down to the centre of the earth. With caster you actually lift up the front of the car (opposite to gravity). Gravity makes the front of the car go down again and therefore put your steering wheel straight after letting go of the steering wheel after a turn.
If the caster is 0, then the front of the car is not lifted up while steering and therefore the steering wheel will not come back automatically.
This is the case if you have a caster of let's say 5 degrees and your driving down hill which has an inclination of 5 degrees. The angle therefore is 0 and the perpendicular line coincide with the pivot line. In that case you will have no caster function.

hemifalcon Tue Apr 22, 2008 3:11 pm

This is beginning to sound funny. If you are driving down a 90 degree slope, then yes, this is true. but otherwise, you are thinking a little too extreme I think. Your car does not become weightless when you are going downhill which is what you seem to be getting at with gravity.

rainierdeklark Tue Apr 22, 2008 3:30 pm

I didn't say that the car becomes weightless. But I did make a mistake in my explanation:
Castor is the angle between the pivot line and the perpendicular line of the surface you're driving on and not the gravity line. Although gravity definitly plays a role in extreme situations.
Anyway, just like you said; I will just put a set of caster shims behind the lower beam.

Max Welton Tue Apr 22, 2008 6:08 pm

Euphonic wrote: I plan on dropping the front of my car practically to the ground and i want to make sure that sterring is still safe.
I assume you will have very little suspension travel? If so, your steering will never be anything I would call safe.

Max

Euphonic Tue Apr 22, 2008 6:43 pm

Max Welton wrote: Euphonic wrote: I plan on dropping the front of my car practically to the ground and i want to make sure that steering is still safe.
I assume you will have very little suspension travel? If so, your steering will never be anything I would call safe.

Max

Haha! True, true... just meant as safe as possible. I dont plan on rally racing my bug either. Just some cruisin' 8)

bill may Wed Apr 23, 2008 1:03 am

rainierdeklark wrote: The whole principle of caster is based on gravity, which is straight down to the centre of the earth. With caster you actually lift up the front of the car (opposite to gravity). Gravity makes the front of the car go down again and therefore put your steering wheel straight after letting go of the steering wheel after a turn.
If the caster is 0, then the front of the car is not lifted up while steering and therefore the steering wheel will not come back automatically.
This is the case if you have a caster of let's say 5 degrees and your driving down hill which has an inclination of 5 degrees. The angle therefore is 0 and the perpendicular line coincide with the pivot line. In that case you will have no caster function.

do not believe anything written here this is complete ignorance. please purchase a bentley workshop manual and read it. also gene bergs tech articles would help you. please don't bash me for calling your nice writing prose stupid.

rainierdeklark Wed Apr 23, 2008 7:37 am

bill may wrote: rainierdeklark wrote: The whole principle of caster is based on gravity, which is straight down to the centre of the earth. With caster you actually lift up the front of the car (opposite to gravity). Gravity makes the front of the car go down again and therefore put your steering wheel straight after letting go of the steering wheel after a turn.
If the caster is 0, then the front of the car is not lifted up while steering and therefore the steering wheel will not come back automatically.
This is the case if you have a caster of let's say 5 degrees and your driving down hill which has an inclination of 5 degrees. The angle therefore is 0 and the perpendicular line coincide with the pivot line. In that case you will have no caster function.

do not believe anything written here this is complete ignorance. please purchase a bentley workshop manual and read it. also gene bergs tech articles would help you. please don't bash me for calling your nice writing prose stupid.

Uh, I already corrected myself a few posts above here....... :?
And the part concerning lifting up the front of your car is definitly true:

"...... Excessive caster angle will make the steering heavier and less responsive, although, in racing, large caster angles are used to improve camber gain in cornering. Caster angles over 10 degrees with radial tires are common. Power steering is usually necessary to overcome the jacking effect from the high caster angle....."



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