HowTo: 4 wheel alignment (toe and thrust angle)

[nhluhr]

Purpose
This is intended to describe the process of doing a 4-wheel alignment on your car using the "Strings" method. This will allow you to set the toe on all 4 wheels individually and with respect to the chassis centerline. This means your Thrust Angle will also be correct after you are done. This article does NOT cover adjustment of camber or caster and it will be assumed that your caster and camber adjustments are correct and equal. This document also assumes that your subframes and unibody are square and true, not bent, twisted, or damaged. If your chassis is true, this document will guide you through the process of performing a four wheel toe and thrust angle alignment.

Background
Toe is something you should re-adjust after every other alignment change. If you adjust camber, re-adjust your toe. If you adjust caster, re-adjust your toe. Additionally, anytime you unbolt something in your suspension linkage (strut, control arm, etc) you should consider at least checking your toe to make sure it's still dead-on. In my experience, no other factor has led to more handling irregularities than incorrect toe. It has a significant impace on the way your car takes corners, tracks a straight line, tramlines on truck-tire grooves, etc. Toe-in is just as likely to cause a wandering front-end as toe-out, depending on the surface you're traveling on.

Likewise, having a thrust angle that is not 0 will make your car take left corners differently from right corners and even makes the vehicle present a lopsided aerodynamic profile to headwind while you're bookin' down the interstate. As you can see, Toe is important. To define "Toe" and "Thrust Angle", these simple diagrams should help:


As you see in the toe diagam, it is typically measured as a pair of wheels. What we will be doing is measuring each wheel with respect to the geometric centerline. This way, the toe is not only corrected on all four wheels, but also ensures that we end up with a 0 thrust angle. As you can see in the second diagram, it is possible to have the two rear wheels both pointing the same angle to one side. If you were to measure toe in the normal way (between both wheels), you'd see 0 toe. However if you measure toe on each wheel individually, you measure one as being toe-out and the other as being toe-in.

Estimated Time for completion
-2 hours or more your first time
-45 minutes with experience, including setup and cleanup

Tools and supplies
Tools required for measurement:
-(4) heavy jackstands
-Bright colored string or heavy fluorescent monofilament fishing line
-a short ruler that reads in very small increments (1/32" or better)

Tools required to adjust:
-22mm Combination Wrench
-19mm Combination Wrench (or large crescent wrench)
-17mm Combination Wrench
-13mm Combination Wrench
-Rubber Mallet

Optional adjustment tools:
-Slip plates (you can make a cheap set out of some parquet floor tiles face-to-face)
-Ramps or jack(make it easier to crawl under the car but require re-setting the car for measurement after each adjustment cycle)

Measurement Procedure
The first step is a test drive. You are looking for a couple things. Namely, does the car wander? Does it tramline more than you think it should? Does it take left corners differently from right corners? Is your steering wheel off-center? Do you have to forcibly hold it off-center to travel in a straight line? Take note of any and all phenomena you can. And I do mean take NOTES. In fact, your success as a home-alignment-technician will depend heavily on your ability to document the characteristics and relate them to the measurements you take.

Next step is to park your car on a nice flat, level smooth surface. If you have slip-plates, park on the plates. The key here is to make sure your steering wheel is exactly centered as you are driving in and that you don't touch it at all once you stop moving the car. Ideally, you line the car up reasonably well, then center the steering wheel exactly, hold it while rolling forward another foot or two, then take your hands off it and never touch it after that until you're ready for your test drive. If your garage floor is not perfectly level, you can use thin parquet floor tiles to build up one side to get the car perfectly level:


Now it is time to setup your measurement rig. This will consist of your four jackstands and the string. Roughly place the front ones about 4" from the fender just in front of the front tire. Likewise, place the rear ones roughly 4" from the fender just behind the rear tire.

Now, tie a loop in the end of the string and loop it over the top of your jackstand.


Run the string to the other jackstand and tie another loop to hold it on.


Now pull the jackstands apart abit so that the string is nice and taut. Raise each jackstand so that the string is at the same height as the centercap on your wheels.


From here, we start to worry about accuracy and precision. We need to use a very finely-graduated ruler for the best accuracy. An awesome friend gave me this ruler with tickmarks for mm and 1/64":


In order to make sure the lines are parallel to the chassis centerline, we imagine the four wheels forming a trapezoid. We then setup our strings so that they are equidistant from the centerline in front and rear which means they may be closer to the rear than the front or vice versa depending on track width:

Vehicle            Front Track    Rear Track    Half Diff (X), in {mm}
2004 STi           58.7           58.5          0.1 {2.5}
2004 WRX Sedan     58.5           58.3          0.1 {2.5}
2004 WRX Wagon     57.7           57.3          0.2 {5.1}
2005 STi           58.7           58.9         -0.1 {-2.5}
2005 WRX Sedan     58.5           58.3          0.1 {2.5}
2005 WRX Wagon     57.7           57.3          0.2 {5.1}
2006 STI           58.7           58.9         -0.1 {-2.5}
2006 WRX Sedan     58.5           58.3          0.1 {2.5}
2006 WRX Wagon     57.7           57.3          0.2 {5.1}
2006 Legacy 2.5iSE 58.9           58.5          0.2 {5.1}

The important thing to note here is the difference in half-track width. This means that your front right wheel will be X inches closer to the string than the rear wheel. Note the 2005STi and 2006STI are the only ones in the table with the rear wheels actually being farther out (and closer to the string).


Armed with this information, you will now move the jackstands close or farther from the car to make them perfectly parallel with chassis-centerline. You do this by measuring off the wheel centercaps to the string. Since the string is thicker than the accuracy of your measurement, choose to measure visually off the inner edge of the string, and always look directly down at the string to the ruler, never at an angle.


Shoot for a nice close-to-the-wheel gap, such as 100mm. This will make measuring easier. For an example, I'll use my 2006 STI. I will first set the string in front as close to 100mm from the centercap as I can. Then, I move to the back and try to get it to 97.5mm (since my rear track is ~5.1mm wider than front, it will be closer to the string and thus smaller measurement - and only half the difference in total track... 2.5mm).

Realize that when you move the front jackstand, the distance at the back will change slightly as well, so you'll have to go back and forth between front and rear a couple times to get it perfect.

Repeat this for the other side.

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[nhluhr]

Now that you have your strings taut, equidistant to centerline, and parallel to chassis centerline, you are ready to make your first toe measurements. From this point on, try not to bump the string or the jackstands at all! Don't open your doors or else they will snag the string and pull a jackstand out of line.

To do this, use a piece of paper and make yourself a quick little diagram like so:


Fill in each blank with the forward and rearward measurement, and take as accurate and precise measurements as you possibly can. Work systematically to prevent getting yourself confused. You will measure from the inner edge of the string directly to the lip of the wheel, first on the leading edge and then on the trailing edge:



Write down your measurements as you go. The difference between the two measurements is the toe for that individual wheel. On the front right wheel in this example, the toe was 0mm:


Continue working and take measurements on all the wheels until you have completed your chart. It doesn't hurt to check that centercap-to-string measurement and make sure it is still at the reference value. It would suck to get bad readings because the string is not exactly where you think it is:


If the measurement from the leading edge of the wheel is larger than the trailing edge, that means the leading is farther from the string, closer to the middle and toe-IN. Now is a good time to go through the measurements and write IN or OUT where applicable to prevent you getting mixed up during the adjustment phase.

As you see in my measurments, I had 0 toe on the front right, 4mm toeIN on my front left, and very slight toeIN on both rear wheels. I won't go into a discussion here of the effects of these misalignments, but instead, we can move right on to the adjustment phase.

[nhluhr]

Adjustment Procedure

Using your toe measurements, you need to now correct the toe on each wheel that is not perfectly aligned. This means the front left wheel and both rear wheels for my example. During this part of the work, it is ideal to NOT jack up the car at all and also to NOT bump the jackstands or strings. This means that after each adjustment, you will be able to check the measurement without having to reset the strings again. This is the real key to making this process go quickly and painlessly. If you absolutely can't reach under the car to make the adjustments, consider parking the car on a few 2x8's or something to gain that extra inch and a half of clearance under the car. If you jack up the car to make an adjustment, you instantly lose the ability to refer to the strings because the car WILL move enough to screw the readings completely.

To adjust the rear, you will use the 17mm, the rubber mallet, and the 22mm. You can substitute the 22mm with a big crescent wrench if you must. On cars that don't have the rear diffusor thingy, you can also opt to use a 22mm socket if you like, but I like working with combination wrenches because they are quick, lightweight, and durable.

Crawl under the rear of your car (Not necessary to jack it up unless you are broly or claustrophobic).

Observe the two lateral links that connect the hub to the middle of the rear subframe. The rear-most lateral link is the toe-adjustment. The adjustment is accomplished using the bolt with the tickmarks on it. Clear? Good.


Since that right rear wheel is slightly toe-in, we need to pull the back of the wheel in a bit to angle the whole wheel towards 0 toe. This means we want to turn the bolt so that it pulls on the rear-most lateral link instead of pushing on it. In the photo above, you can see that the bolt head has a "cam" shape built into it and turning it will displace the center of the bolt slightly left or right to pull or push on the lateral link.

Stick your 17mm on the nut on the backside of that bolt. Hit it with the rubber mallet to help loosen it. Loosen it enough so that you can turn the nut without the mallet then take it another half turn or so. You don't want it completely sloppy loose.

Stick your 22mm (or crescent) on the bolt head with the tickmarks. Turn it so that the cam forces the lateral link to be pushed in the direction it needs to be.

Grab your mallet and whack the rearward edge of the tire a few times to help push it out (this happens easier with slip plates in place).

Go back to your string and take a quick measurement. If it's perfect, crawl back under and tighten down the 17mm nut, making sure the bolt doesn't turn AT ALL. If the bolt turns, you're screwed and you need to adjust it again. Hit the end of the wrench with the rubber mallet poor-man-impact-gun and tighten the nut to a nice tight high-torque setting.

Measure the toe once more just to make sure. If it's not quite right, adjust again. If it's fine, move on to the next wheel.

Once you have completed both rear wheels, move to the front. It's very tight under there, but the good thing is you SHOULD be able to reach what you need to and it's actually a little easier than the rear.

Locate the tie rod under the car. It is the metal rod that goes from the steering rack to the hub and it's on the front side of the hub. Locate the 19mm nut on the rod that prevents it from being changed. Take your 19mm open ended wrench (or large crescent wrench) and loosen that nut. On the right side with the wrench pointing down, you will have to push the wrench towards the rear to loosen the nut. Vice versa for the left front wheel - pull the wrench towards the front to loosen it. If you can't get it to loosen, get a bigger wrench or use your poor-man's impact technique (mallet hitting end of wrench) on it.


Once you get the nut loosened, take your 13mm and turn the rod the appropriate direction. If the wheel is toe-in, like it is in our example front-left wheel, you will need to "lengthen" the rod by 'unscrewing' it a bit. I have found that 4mm of toe is corrected by roughly a half turn of the rod. Some say that each "facet" of the tie rod (1/6 of a turn) is approximately 1mm of toe adjustment.

Remember, the rod screws into the rod-end so to help visualize which way to turn it, imagine yourself at the steering rack looking at the wheel and just unscrew it towards yourself.

Once you get the adjustment, finger-tighten the 19mm nut, then tighten it down with the 19mm wrench. The Ball Joint on the tierod-End will allow some play so try to turn the 13mm part with the 19mm part until the ball joint bottoms out against itself to prevent losing your precise adjustment.

It is NOT necessary to get this gorilla-tight. Just a pretty firm tug so that it won't come loose on it's own. I have NEVER had a tie-rod nut come loose on me. Plus, you might have to re-adjust it again after you check your measurements. I would suggest after you tighten the nut, turn the rod-end back a bit to make the balljoint roughly in the center of its articulation.

Once you get your first front wheel adjusted, move right on to the next one. You will repeat the measure/adjust/measure until everything is perfect front and rear. Again, I suggest using the ruler to measure the centercap-to-string frequently to ensure you are not drifting at all.

Once you think it's all perfect, roll the car back about 3 feet, then roll it forward again (steering wheel perfectly straight). Do a quick re-setting of the strings to get them nice and parallel, etc... Re-measure to ensure everything is just exactly where it should be. If it is, then you can go for a test drive!

[nhluhr]

Torque Specs:
Rear Lateral Link, Inner Attachment Bolt/Nut - 74 ft-lbs
Tie Rod LockNut - 62 ft-lbs

[PossumK]

Stick your 22mm (or crescent) on the bolt head with the tickmarks. Turn it so that the cam forces the lateral link to be pushed in the direction it needs to be.

Grab your mallet and whack the rearward edge of the tire a few times to help push it out (this happens easier with slip plates in place).

Is it necessary to hit the tire with a mallet before tightening the bolt, or is this step only for allowing immediate measurement?

Excellent write-up. The release timing was perfect for me.

[nhluhr]

Well, if you feel that your adjustment didn't actually move the lateral link (because you didn't turn it enough to take up slack and start pushing/pulling) then hitting the tire will jar it loose. The main idea of hitting the tire though is that the rubber tire will resist the wheel twisting and when you adjust, you may just compress the linkage bushings a bit... then when you drive, the tire won't be at the correct toe you thought it was. This is also the main reason for the last step being to back the car up, roll back forward, and re-measure.

The better your slip plates are, the less you have to worry about this.

[Mykl]

You sir, are the man.

[DrBiggly]

This is absolutely a definitive guide for how to do one's own alignment at home.

-Biggly

[Unabomber]

Wow Nick.....I'm shocked at the accuracy here. I suck, you have teh win!

<----will write a new FAQ to restore my manhood

[BIGSKYWRX]

Very nice!

[Turn in Concepts]

Hey Nick -

3 things -

1) if I were a mod this would be stickied by now.
2) like your last set of well written instructions this needs to be on scoobymods
3) See if you can find out the thread pitch of the tie rods so you can give an idea of how much of a turn will affect how much toe. For example, 1 full turn makes an adjustment of 1.5mm (or whatever it is)

[nhluhr]

Originally Posted by Turn in Concepts

Hey Nick -

3 things -

1) if I were a mod this would be stickied by now.
2) like your last set of well written instructions this needs to be on scoobymods
3) See if you can find out the thread pitch of the tie rods so you can give an idea of how much of a turn will affect how much toe. For example, 1 full turn makes an adjustment of 1.5mm (or whatever it is)

The thread pitch is 1.25 mm per thread.

At first one might thin that means if you move the rod 1 full turn, then you'd gain 1.25mm of toe.... but that's not right. The tie rod attaches somewhere in the range of 'half' the distance from the hub to the rim lip where we are measuring.... so if we pull the hub 1mm in there, the rim lip might move 2mm or so... and that would be a change of 4mm toe since you're also pulling the rear in... What I've found practically is that a little more than a half turn of the rod will correct roughly 4mm of toe...

[Mind]

Excellent. Thank you.

[Vikingmoose]

Excellent write-up. I've really wanted to try this at home but never knew how to go about it. THANK YOU!

[Mykl]

nhluhr, thanks again. This writeup is invaluable to me having recently installed coilovers on my car. With a way to measure camber, which shouldn't cost too much, I can pretty much do whatever I want now. It's a shame I don't have an expensive set of scales so I could play with the corner weights...

[GFimpreza]

Thank You!

[S.G.D]

This is great!

Thanks!!

[Arnie]

IIRC, one facet of adjustment on the tie rod equals 1/16"

[Bishop]

wow great write up!! Sticky ASAP!!!

[nhluhr]

Originally Posted by Arnie

IIRC, one facet of adjustment on the tie rod equals 1/16"

are you saying 1/6th of a rotation = 1/16" toe adjustment?

[Arnie]

There 6 sides to the tie rod, correct? If so, yes. If you move the flat(facet) to its next position, that's 1/16 of an inch of toe movement. I should point Mako here, he's our resident socal alignment freak.

[makofoto]

each facet is equal to about 1 mm. 1.6 mm = 1/16th inch.

Subaru oem specs are plus or minus 3 mm!

[Arnie]

Thanks Mako!

[makofoto]

An aggressive everyday street setting, that doesn't use up the tires is 1/16th TOTAL toe out ... less then oem "limits."

[Arnie]

so 1/32 toe out per side? you've got some accurate shelves mako!