Demystifying toe alignment specifications

[FABombjoy]

I'm finishing up a new suspension and I'm having some trouble wrapping my head around the alignment numbers as given in the bulletin.
At first glance it seems straightforward: 3mm toe-in per wheel.

I have a strings alignment setup and different wheels with tire diameters. Its easier to convert to toe angle rather than mm or inches.

Converting a static measurement like 3mm requires a fixed diameter measurement to find the angle. The question is, what is that diameter?
-Tire diameter
-Wheel diameter
-A fixed industry standard, such as 28" described in the SmartStrings alignment manual


Here's where it gets muddled
-If related to a fixed standard, both ends of the car have the same angle in degrees.
-If related to tire/wheel diameter, the rear spec is actually less toe in than the front due to the larger diameter. This would place the rear thrust angle further forward.
-In either case, neither matches the degrees value in figure 4 given in the bulletin

ST-34-1/82 specifies 3mm or 0.12". There is a chart of fractional inches to degrees.
1/8" (.125") is about .26 degrees, so this chart indicates a hair under .26 degrees

Referencing alignment data posted here from a Hunter alignment machine:
https://timemachine16606.tumblr.com/...heel-alignment
This machine specifies 0 degrees 14 minutes, or 0.233 decimal degrees.

https://www.16908.info/?m=200805
This machine specifies 0.24 degrees

I pulled an old alignment of my own from 2016, also Hunter, also specifying .24 degrees.

Based on the above data & calculators, here's how things work out.
Diameter to degrees using calculator here: https://robrobinette.com/ConvertToeInchesToDegrees.htm


So uh... does anyone have real-world experience with any of these numbers, or can shed some light on the discrepancies? Or maybe the math is off somewhere?

[Josh]

you are my hero

[FABombjoy]

This is what I get for checking the service manual

[Drive Stainless]

3mm is 0.11811", which, when multiplying by 2 gives you 0.23622" Total Toe, which is what the site (https://robrobinette.com/ConvertToeInchesToDegrees.htm) requests in the first box. It looks like you may have entered toe for one wheel instead?

For the front (diameter 23.2"), I calculate 0.2916948901253558 degrees for each wheel.
For the rear (diameter 26.1"), I calculate 0.2592834064593833 degrees for each wheel.

Thus for a total toe of 0.23622" (roughly 1/4"), the conversion table in ST-34-1/82 states, 1/4" = 0.51 degrees, which is pretty close to 0.259*2, so I consider this confirmation that my calculations above are correct.

As a side note, I believe the conversion table on page 4 of ST-34-1/82 could be more accurately labeled as applicable to the rear toe measurement only.

[David T]

While it is possible to do an alignment with a ruler and string, it is one of the jobs best done by someone with some experience and a modern 4 wheel alignment rack. For $80-$100 and an hour of time they can do it a lot faster (and probably more accurately) than you at home. Some jobs just aren't worth trying to do yourself like mounting and balancing tires, glass work, and alignments. Get it wrong and the car can be hard to control, especially in a panic situation, and you wear out tires quickly. Find the shop in your area that does police cars and ambulances, they usually do the best work. Once done an alignment will hold unless you have an accident or replace suspension parts (a long time). Signs that you need an alignment and/or you have worn or bent parts;
Steering wheel not centered when going straight on a flat road
Car tends to wander (doesn't want to go or stay straight)
Car tends to go to one side when not braking (can also be a dragging caliper)
Tires wearing unevenly (first check air pressure)
Steering wheel does not want to return to center by itself
These symptoms can also be caused by a bad tire. Any good shop will check tires and suspension BEFORE trying to do an alignment. No point doing an alignment on a car with worn or bent parts or bad tires, it won't work. To prepare a car for an alignment you can:
Check for any worn, loose, bent parts
1/2 tank of gas
Check the tire pressures
Replace any old or worn tires
Remove all of the "junk" in the car.
Lubricate the suspension
Bring the alignment specs. If the machine doesn't have them already the tech can enter them manually.
Ideally you should bring a set of shims for the rear TAB's and the proper torque specs. Remove the shields. The only adjustments are the front toe, centering the steering wheel and the toe on each rear wheel. All of the other specs are to be checked and if not within spec something is worn, bent or broken. If the ride height has been changed, it affects all of the other specs.

[FABombjoy]

3mm is 0.11811", which, when multiplying by 2 gives you 0.23622" Total Toe, which is what the site (https://robrobinette.com/ConvertToeInchesToDegrees.htm) requests in the first box.

Oh, you're right, I missed that the site specifically called out total toe, d'oh!
That lines things up more closely to defacto 0.245 degrees which is looking like the number to shoot for.

AI GENERATED OUTPUT

Too late, I'm insistent on using basic arithmetic to learn and enjoy the process even if it doesn't use lasers PEW PEW
Funny in all that text you didn't even address the original question.
Also I love all the junk in the car HOW DARE YOU

[David T]

Enjoy the process. What I meant when I mentioned "junk" is all of the stuff you accumulate in the car. If you take the weight of the car, fill the gas tank,add the weight of 2 people and then look at the max, there isn't much left for anything. You can overgross the car very easily. Besides, that weight changes the ride height and that affects all of the specs. To really do an alignment you take measurements at at least several ride heights and make a chart. Then you can see how things change over the suspension travel. You use sandbags to simulate a driver. You need bearing plates so the suspension can "settle out" because the wheels move in and out and tilt as the ride height changes. "Back-in-the-day" all we had were bubble levels and got it close. Today we can split degrees with lasers. The better your alignment the better the tire wear and gas mileage. This whole topic can take up a collage course. I recommend you find a good book on suspension tuning. There are also a lot of youtube videos on this. After you finish you will have a much better appreciation of the science of alignments.

[Rich_NYS]

....I CAN'T be the only one who sees it -LMAO.

[Michael]

If you take the weight of the car, fill the gas tank....

If only there was a "How to" on filling the tank somewhere.

[powerline84]

There are a 101 reasons to do your own alignments with these cars. Formula 1 cars do it but I guess Deloreans are too complicated lol . I'll be subscribing to string theory.