IRS alignment setting for wide rear tires

[AIRSICK]

Originally Posted by Sandeep

Yes the mod did work. You have to rotate the rear of the trailing arm up in relation to the springplate.

Sandeep

Thanks for the reply Sandeep. I took my rear suspension apart last night and fond that I have 4 bolt on the spring plate. The previous posts only mention 3.
The bolt closest to the torsion housing is threaded into the trialing arm and the bolt does not stick through the inboard spring plate. The other three bolts go in trough the inboard spring plate, through the trailing arm and out past the outboard spring plate where there is a spring washer and a nut.

This brings up two questions:

Which bolt do you want to use as the pivot point for the TA to rotate about?
Why can't you slot the TA holes vertically instead of over sizing the holes in the spring plates so you have movement in two axis? (There's not much meat around the rear spring plate slots.)

[boygenius]

I think that only the 1969 beetle had double sided spring plates while every year after that had an easier to work with single spring plate. The single spring plates only use three while the double spring plates use 4 bolts.

When you enlarge the the spring plate hole you allow the TA to rotate either counter-clockwise or clockwise which changes the camber of the rear suspension.

Am I correct???

[AIRSICK]

Thanks for the info on the spring plates. I thought that because the slots in the spring plates are elongated horizontally already for toe adjustment that I could elongate the holes in the TA vertically and that way I would have adjustment both up and down and front to rear without over sizing the spring plate holes.

But I still need to know if I use the middle bolt for the rotation center or the forward one closest to the torsion housing.

[Bruce2]

Originally Posted by Sandeep

So thanks again Bruce2 for the suggestion and direction as you've probably saved me atleast $1000 in rear tires. :bowdown: :haveadrin

Sandeep

Good to hear that. Beer's on you if we ever meet!

[juse]

Originally Posted by Sandeep

Yes the mod did work. You have to rotate the rear of the trailing arm up in relation to the springplate.

Sandeep

I´ll better go trough what I`ve learned from the earlier posts:
-When you lower rear IRS suspension, tires get negative camber.
-For even tire wear and good handling performance, you want to get rear tires near zero camber.
-When you put those two statements together you get:

After lowering your IRS rear suspension you need de-cambering, right?

-One way of de-cambering is to move the inner pivots of trailing arms upwards.
-This can be done with a camber-box familiar from Porsches, or maybe by fabricating a DIY mounting, higher than the original one.
-Again we couple the two earlier statements and get a question that I`m interested of:

If you move the inner IRS mount upwards the same amount that you have lowered your rear suspension, do you get stock camber???

Justin

[Panelfantastic]

My bus has bolt on IRS pivots, so I was able to loosen and turn them to get the negative camber out... but, the amount I rotated them did not seem consisitent with the amount the bus was lowered. Several inches on lowering but it took a lot less than that to correct the camber. Sorry I didn't take exact measurments at the time but I would say it was less than half the amount. No way to gaurantee that this would translate the same to your project but maybe it helps?

Jeff.

[juse]

My project is a `63 pan and a ´61 body. A mixture by coincidence, nothing special.
But I would like to get The IRS conversion welded into it before getting it sandblasted and painted.
Has anybody else any thoughts or experiences on this, "rear-lowering to pivot-lifting ratio"?
Justin

[Sandeep]

I too would like to see a beetle with adjustable inner pivots done to a stock IRS pan. I would do this in the future when my car is a weekend/warrior only as currently it is a daily driver in the summer

My rear is lowered to the point that if I had the stock snubbers for a '74, I would be riding on them I've cut mine down to about half the height and I have acceptable travel. I have -1.15 deg on the drivers side and -1.28 on the passengers side and it corners beautifully.

Sandeep

[juse]

Panelfanstic: your setup might not be directly comparable to a bug, but close. Thanks for your opinion.
Sandeep: so you made an adjustment similar to Porsche 924/944. OK, but I want zero camber, and I dont need an adjustment...hopefully.
But has anyone done an adjustable or fixed camber-box into a beetle???
Justin

[Michael Ghia]

Originally Posted by juse

Panelfanstic: your setup might not be directly comparable to a bug, but close. Thanks for your opinion.
Sandeep: so you made an adjustment similar to Porsche 924/944. OK, but I want zero camber, and I dont need an adjustment...hopefully.
But has anyone done an adjustable or fixed camber-box into a beetle???
Justin

Justin,
You don't want zero camber, it'll handle like a pig!
I spent a lot of time on my Oval swapping the rear IRS arms over side to side (relocating the shocker mount on the other side of each arm etc) to get zero (or close to) camber. I achieved it too... but it would not handle. I tried different tracking settings, but as I had swapped the arms over I was limited to about 0.3 negative camber and the car simply would not go around corners, apart from sideways () which is great for fun but not when you want to go fast.

If you look at factory settings for the Beetle, they are listed as -1o + or - '40.
So negative camber does not always equal tire wear.. but mis-alignment and over the top settings will.
The factory setting for the 944 are similar at -1o + or - '20.

MG

[juse]

OK. So -1 degree would be ideal?
Somekind of chart of lowering factors would be useful. For example: if you lower stock IRS rear suspension 10mm you get 1.5 negative camber and so on.
Has anyone taken such measurements?
I`m planning to weld my IRS-jig this weekend, and all hints concerning of repositioning the inner pivot for decambering are welcomed.
Justin

[Michael Ghia]

Justin,
As the camber alters as you move the arm in relation to the spring plate, the camber could be anything as you have to disturb the bolts between the 2 items mentioned above.
Basically you should be able to choose your camber setting at most suspension heights... that is not including the extremes... very high and very low.

MG

[rip]

Originally Posted by Michael Ghia

Bruce,
Are you sure? Think about it as simply jacking the car up and down. If you jack the car up (the suspension arm goes down) you get positive camber and if you lower the car down (the suspension arm goes up) you get negative camber....

Mike

eh? I'm having a bit of trouble understanding this, where is the axis of rotation? I thought michael ghia was right, but if he's not...

See I thought that because the trailing arm was well rigid I thought the motion was with in it's path thus as the arm moved up the arc of the path pulled the end of the arm towards the center of the car.

I fail to see how the arms motion could be along an axis other than this, unless there was binding, and okay I see that there could be some binding but not a lot. but to move away from this axis to provide positive camber is hard to see.

[rip]

Originally Posted by Bruce2

Positive Mike (pun intended)

As the stock suspension articulates, the pivot point is not the TA's inner pivot. It is also not the center of the torsion bar at the spring plate. It is along a line drawn between these two points. Because this line is not parallel to the torsion bar but tilted back as it extends from the spring plate's axis to the center of the car, the TA goes negative camber when the TA goes up.

Now loosen the 3 bolts between the TA and SP. The new axis is along a line from where the 3 bolts are to the TA's inner pivot. This line is tilted opposite of the one above, so therefore camber changes are opposite.

and all though I havn't lowered my car yet, even with irs should you get a little bit of the neg camber.

The way I'm picturing this is; where ever the axis of rotation is to draw a mental perpendicular radius or moment arm to the point in question, then to following the arm as it rotations under a constant distance.

help please

[Bill K.]

Originally Posted by Sandeep

Well, I've completed Bruce2's method of alignment to get +ve camber and I am happy to report that it works !

I've only completed the mod on the passengers side rear and went from -2.93 deg to -1.38 deg measured using a bubble level and some trig. I filed the two rear bolt holes from slots into what looks like a "D" rotated 90 deg CCW. I could get more +ve camber if I wanted but my arms got tired from all the filing work !

So thanks again Bruce2 for the suggestion and direction as you've probably saved me atleast $1000 in rear tires. :bowdown: :haveadrin

Sandeep

Sandeep - I have SAW adjustable spring plates to install and want to correct for excessive negative camber as you did.

My trailing arm has 4 holes (1 threaded in front, 3 through in rear) -- its a 70 standard with the double plate spring plates. The SAW spring plates have only the rear 3 slots. Do I need to drill a hole in the SAW spring plate for the front (threaded) mount in the trailing arm? Or, just use the three rear mounts?

When enlarging the spring plate slots, how much material did you remove along the top of the slot? 0.05", 0.10" ?

Only enlarge the rear TWO slots so the trailing arm can pivot up about the unmodified front bolt #3 (not bolt#4, the threaded one in the trailing arm, '69-70 only)?

Thanks for the help,
Bill