jlwdvm

I am measuring at the wheel flanges with a string that is squared up at the rear wheel and ran forward to the front wheel. The 1/8" measurement is the toe I get at the wheel flange. Why is it necessary to roll the car back and forth after adjusting the toe?

Norm Peterson

Because unless you have toe plates or some otherwise very slick contact somewhere between your tires and the ground you will develop friction that will affect your measurements. What this does is allow the control arm bushings to compress differently after adjustment relative to before, and the bottom line is that you'll be making somewhat larger changes than you measure. IOW, the bushings "absorb" some unknown amount of the toe rotation that your adjustments are trying to make. Stiff short-sidewall tires on rims that are relatively wide compared to the tire size exaggerate this effect, softish tires on narrow rims tend to minimize it. Poly front LCA bushings or rod ends greatly reduce it compared to OE rubber bushings. But it's always there, because everything flexes at least a tiny bit under load (even the chassis-side brackets that you bolt through!).

For very small changes, this effect is probably not significant, but I wouldn't ignore it at the 1/8" / 0.25° level - and certainly not if your front LCAs are still running the OE bushings. Down in the range of adjustments below 1/32" / 0.05°, I probably would.


Edit and FWIW, don't assume that your rear wheel faces are parallel to each other. A stick axle does not have to have zero toe or camber angles just because you can't easily change whatever angles it actually does have. I'd extend your strings to in front of and behind the car so that I could easily check the distances between them for parallelism.


Norm

JAJ

Yes, there is a ratio: a movement of one flat (1/6th of a full turn) on the tie rod will change the measured toe difference between the front lip and rearward lip of a 19" rim by 0.040".

So, if Norm's guess that 1/8" at the tire is 0.080" at the rim lip, then I'd adjust each side by one flat (to keep the steering wheel straight) and that should give you about 0 toe in.

A word of advice: when I do these adjustments on mine, I put the car in the air and clean all the dirt off the tie rod and rod end. Then I put masking tape around the tie rod and the rod end and mark my starting point and end point. Once you have it loose, it's way too easy to lose track of where you are, so pre-marking makes it harder to make a mistake. That, and you're working upside down on your back, at least I am, so keeping track of which way you have to turn things is important too.

I've made adjustments as small as 1/2 a flat on mine. My toe is exactly zero and my steeing wheel's straight. I use fishing line and a dial indicator to measure my settings.

JAJ

That's my method too. Two sticks, 7' long, with sharp notches to align the fishing line. I sit them on top of four jack stands, two ahead of the car and two behind. I center the strings on the front hubs, and offset them by the lateral displacement of the rear axle - 1/8" on my car. This aligns the strings to the centerline of the chassis. I also adjust the height of the strings to cross the centerline of the wheel center cap. If you don't measure at the exact same height on the front and back of the rim flange, the inward tilt of the rim (negative camber) will introduce a measurement error. Precise toe setting requires your overall error to be 0.010" or less, so every little thing counts.

As Norm said, before you measure toe, you need to have the steering wheel exactly "level" in front of the driver's seat and you have to roll the car back about 2 feet or so and then forward to the measuring position. The toe itself loads the bushings, so if you roll backwards before you measure you'll get a different reading than if you roll forwards.

jlwdvm

Good info! Thanks. Back to the drawing board tonight.

jlwdvm

Worked on it last night and have more questions:
1. I ran a string along each side of the car that passed through each wheel center and measured between the strings front and back to make sure they were parallel. How do you know the car is parallel with the lines? The strings can be parallel, but the car could be parked askew between them. I tried to square the lines up with the front and rear wheel surface.
2. How do you know the steering wheel is where it needs to be? After adjustments, I would move the steering wheel until one front wheel has parallel to the strings, then measure the other to see if it had toe in/toe out. On my final measurement, I had basically 0 toe on each side (taking into consideration that my strings were probably not exactly perfect).
3. Is an alignment shop going to be able to get it any better? I have adjustable camber plates, so the only thing I would need them to check would be toe.
4. Do you always adjust both sides equal amounts, or is it ok to adjust one side alone to bring that side into spec?
Thanks!

Norm Peterson

For most purposes, if the car isn't too much 'skew', that should get you close enough to get the total toe good.


That's one way. If you trust your efforts at getting the strings parallel to the car centerline (which is probably more difficult with a PHB equipped rear suspension), you can simply match the toe readings to whatever individual toe you want.

What I normally do next regardless is drive the car and see where the steering wheel wants to be when going straight. If it's a little off, I'll adjust one toe in the 'out' direction and the other by an equal amount in the 'in' direction.


Maybe. That depends on the technician and the shop. From scratch to done they'd be quicker (not counting the time for you to drive there, wait for your car to be driven onto the rack, adjusted, pay, and drive beck home).


If you start with the steering wheel straight (and it was straight before disassembling the suspension for your mods), you should be able to rough-set the individual toes to be close enough to zero before worrying about making unequal adjustments (just keep aware of the steering wheel moving if it doesn't center in a steering wheel lock position and straighten one side out as best you can first before starting on the other). Chances are, the total amounts of right-side and left-side adjustments won't be exactly equal when you've finished.


Norm

safetyfastgt

With adjustable camber plates, won't the toe in be affected each time the came is adjusted?

Norm Peterson

Yes. Toe normally varies regardless of where you make your camber adjustment, and that's why toe is done as the last alignment adjustment.

The closer the height of the tie rod joint is to the ball joint height (referenced to the ground), the smaller this effect will be.


Norm

JAJ

Yes, but not by much. I have the Steeda adjustable upper mounts and if I switch from fully out (-1.4 degrees camber) to fully in (-2.4 degrees camber), I go from 0.000" of toe to 0.008" toe-in per side (0.016" total toe-in).

On the questions, Norm pretty much called it:

1. As Norm says, so long as the strings are parallel, it's not critical that they line up on the centerline of the car. If you want to get it straight exactly though, here's how I do it:

- Get a construction level and stand it up vertically against the rear fender lip and measure from the level to the face of the rear hub center cap. Do both sides. One side will be further than the other. Divide the difference in half - I'll refer to this number as "A", and it's a measure of how far the axle is sitting off the centerline. Mine is shifted 1/8" to the driver's side.

- Set up your strings. Align the strings so that they are exactly the same distance apart at the front and rear. Center the car between them as follows:

--at the front, measure from the center of the wheel hub cap to the string - it should be the same on both sides.

--At the rear, measure from the center of the hub cap to the string but subtract "A" from the short side and add "A" to the longer side as measured above.

This centers the chassis between the strings at both the front and the rear.

2. I sit in the drivers seat and line up the arms of the steering wheel with the outline of the cowling ahead of it. If it's visually straight, then it's centered. No magic involved. This position is the position you want the wheel to be in when you're driving straight down a level road, so your goal is to set the toe with the wheel in this position. As Norm says, once you've done an adjustment, drive on a straight and level piece of road and see if the wheel's straight. Fix it by adding a little to one side and taking the same off the other. I did that adjustment 1/2 a flat at a time until mine was straight.

3. No. I was chatting with the crew chief of Bullet Racing (they run a Porsche GT3 at the 24 hours of Daytona every year) while he was aligning one of their race cars. He had it on a portable rack standing on wheel stands and he was using a fishing line kit to adjust the rear and front toe. He said that his experience is that "the strings never lie" while even a freshly calibrated laser rig can give you the wrong answer.

4. to put what Norm said a different way, you can do it any way you like so long as the steering wheel ends up "mostly straight". It makes me crazy when mine's not perfect, so I trimmed it until it was. If a little crooked doesn't bother you, then adjusting only one side is fine. That said, don't let it be very far off - EPAS is going to assume straight with a small tolerance, so if it's off by more than an inch or so at the steering wheel rim, then I'd take a little off one side and add the same to the other to get it straightened up.