Flipping IRS Control Arms

[sideshow]

Just doing some mental bench racing, but ?When does it make sense to flip the control arms on an IRS car??

I don't know a much about this, from memory there is 1.5 degrees of negative camber built into the stock suspension. Flipping the arm and relocating the shock mount will give 3 degrees positive camber. Lowering decambers the rear.

I used a straight edge & harbor freight angle finder;

• At static ride height has negative camber of about 2 degrees
  Unloading the rear suspension (jack under the front mount) and it is about 2 positive

This is primarily a street car, daily driver. I think I went 2 splines on the outboard and Avis'ed up front. It is an early 68 Ghia, was an Autostick, and secondary reason I bring this up is that I have an ?grasshopper? from a station wagon and at some point in time I will swap bars, brakes, after sending the parts to the powdercoater.

So in my case, stock looks to be the best choice. In theory having 1 degree positive camber at static ride isn't worth the effort.

Any thoughts on when flipping makes sense, how hard is it, and any success and or failure stories to share?

[gcorrado]

flipping the control arms makes sense when you want to lower without introducing large static negative camber.

to get the best road holding possible you want:
1) a low center of gravity
2) a camber near zero when the car is turning hard.

one of the biggest perks of semi-trailing arms over swing axles is that ther is MUCH less camber and toe change with suspension movement. still there is some. as you say, camber goes more negative as suspension is compressed.

it's true that 2 deg static negative camber is more than you want. maximum cornering force is slightly reduced, your tires are wearing faster, and the rear of your car is less stable over unevenness in the pavement.

is 1 deg of static positive camber desireable? not really, though you could argue that it's slightly better than what you have now.

it is not any easy job, and the gain would be only marginal. i would do it only if you plan on lowering the rear even more at the same time. then you'd be getting the center of gravity even lower AND have a 0 static camber - that's having your cake and eating it too.

[Marc]

For a maximum contact patch you do want the tire to be at zero camber, but that's in relation to the pavement. Unless your car has zero body roll (no suspension) you'll need some negative camber at rest in order to achieve this, there isn't enough rear camber change to do so automatically as the suspension travels.
By nature, the front suspension has no camber change as it moves through its travel, making it even more important to have some negative (static) camber in order to keep the tire square with the ground when cornering.

[gcorrado]

For a maximum contact patch you do want the tire to be at zero camber, but that's in relation to the pavement.

right on, i couldn't agree more.

you'll need some negative camber at rest in order to achieve this, there isn't enough rear camber change to do so automatically as the suspension travels.

i didn't realize this was the case for semi-trailing arm suspension. can you help me understand, marc?

are you saying the positive change in body angle is always greater than then negative change in angle with suspension travel, even with the center of gravity held at the same height? this is something that could be tested on a car at rest.

or are you saying that even on an IRS car the roll center is high enough to get center of gravity jacking? this car is literally lifting and tipping, and this ands enough positive camber to cancel the change from suspension compression. this is of course what's famously bad about swing axle cars.

By nature, the front suspension has no camber change as it moves through its travel, making it even more important to have some negative (static) camber in order to keep the tire square with the ground when cornering.

absolutely! the front suspension of standard beetles is pure (not semi) trailing arm, and so there is no camber change with suspension compression. this means the angle the wheel makes with the ground is the same as the angle the nose makes with the ground. up front static negative camber seems like an unfortunate reality. you need to get the extra eccentric bushings that bugpack and others sell. i'd run about 1/2 a degree of negative camber up front for the street. on the track, run as much negative as you can - ususually in the neighborhood of -2.5 deg.

do you concur, marc?

[Theo]

Along these lines, how much dynamic camber does an increase in caster create in the front? I'm using one beam shim now but I've been told I should use two shims to max out the caster. I have not had a profesional alignment so I don't know how much caster or camber I have.

I have the aftermarket ecentric bushings maxed. It has visible negative camber.


Thanks,

Theo

By nature, the front suspension has no camber change as it moves through its travel, making it even more important to have some negative (static) camber in order to keep the tire square with the ground when cornering.

absolutely! the front suspension of standard beetles is pure (not semi) trailing arm, and so there is no camber change with suspension compression. this means the angle the wheel makes with the ground is the same as the angle the nose makes with the ground. up front static negative camber seems like an unfortunate reality. you need to get the extra eccentric bushings that bugpack and others sell. i'd run about 1/2 a degree of negative camber up front for the street. on the track, run as much negative as you can - ususually in the neighborhood of -2.5 deg.

do you concur, marc?

[gcorrado]

I'm using one beam shim now but I've been told I should use two shims to max out the caster.

i've had kind of the same debate going on my head, one shim or two. let me do a bit of research and see if i can dig up a good answer. input, marc?

[sideshow]

Yea I kinda figured unless I went a couple more degrees negative it really wouldn't be worth it.

Where I am now is about as low as I am going, I replaced too many exhaust parts in the past and really don't want get good at again . I just hate the idea of nicely coating control arms, followed by cutting and welding the shock pocket to the other side.

[sideshow]

I like caster shims.

At the alignment rack I had ~2.6-2.8 degrees. Then again I run small tires 135r15, Berg's 3.4 degree shims, and the stock wheel.

So one only needs one shim, the big question is which one 1.5 or 3.4?