Do It Yourself Alignment On A Miata
I have always had issues getting alignment numbers that I wanted when I took my Miata to alignment shops. Probably over half of all alignments ended with the technician saying "you are maxed out on camber at this corner at X degrees, I cannot give you Y degrees you asked for". This was understandable when the car had stock suspension and Y was over -1 degrees, but after installing race shocks and lowering the car hearing the same for -2 degrees was disturbing. When I had the shocks just installed the alignment I got was -3 degrees of front camber and -3.5 degrees rear camber; how could I be maxed out at -2 degrees now? Then, I started hearing "I cannot reduce rear camber beyond X which limits front camber to Y given your desired Z front to rear difference", where X was surprisingly still -2. It cannot be both ways, right?
Eventually I got tired of that and ordered V8 Roadsters control arms advertised as giving additional 2 degrees of camber adjustment either way at each corner by means of an additional eccentric. I was pretty shocked to receive the car from alignment with the same exact numbers as I had before and the same exact verdict - "you are maxed out on this corner".
Add to that having to argue with alignment shops to put driver's weight in the car before alignment, having to argue over whether a 0.5 degree camber difference left to right is acceptable, not knowing what my alignment is during the season and if it is time to fix it, seeing everything from reasonable to outrageous prices, and last but not least, having the car aligned on towing wheels which have 3 different sized tires on them and then eccentrics spot welded (clearly I forgot to leave my race wheels with the car, but are these guys paying attention at all?) I decided to take matters into my own hands.
Leveling The Car
The first thing I had to figure out was how to get the car level.
Lucky for me I have an open car trailer. It is straightforward to level the trailer by adjusting the jack height and letting air out of the tires. The trailer has a beaver tail which is not level, but the car just fits on the flat part of the deck forward of the beaver tail.
The second thing that an open trailer with an open deck allows is access to all of the suspension bolts under the car.
If you do not have an open deck car trailer, you can get a set of hub stands for $800, but then you need to find a level surface still.
I do not have a CNC machine at my apartment to fabricate camber/caster gauges, thus off the shelf tools would be used.
I align the car by myself therefore the tools should ideally be easily usable by a single person.
For toe, I elected to go with a Longacre toe bar after talking to a Longacre tech. He recommended the toe bar for one person alignments, and it makes the job much easier.
For camber, I settled on a Longacre digital camber/caster gauge with AccuLevel and QuickSet LW Adapter. I think reading a number ought to take less time than reading markings next to a vial, and the digital gauge is accurate to 0.1 degrees as opposed to 0.25 degrees for a vial gauge.
Unless you have a stock (as in oval racing) car, the various hub adapters that Longacre makes are not going to work. Their QuickSet adapters however go into wheels just like the ones in alignment shops do. The LW version is good for wheels from 13" to 22" - in particular, it works for 18" and 19" wheels whereas the standard QuickSet is for wheels up to 17" only. I used the LW adapter with 15" wheels and found no issues.
Once you have a camber gauge you can use it to speed up the alignment process as follows:
- When you get a reading you know how far off you are. For a 0.5 degree difference from your desired camber, you need a small adjustment. For a 3 degree difference, you need a big adjustment. As you are making the adjustments, you can correlate how much you move the bolt vs how much the camber changes by.
- Instead of leveling the car, you can take a measurement of the slope it is on and account for it in your setup. For example, supposing the car is on a 0.5 degree slope left to right, if your target is -3 degrees front camber, you would dial -3.5 degrees of camber on the left and -2.5 degrees of camber on the right.
You will need tools to adjust suspension components. On a Miata all eccentrics use 17mm bolts, but even so I ended up using a racheting wrench with a 17mm socket and an extension, a 17mm socket without an extension and a 17mm combination wrench to get to different bolts. You will also need to adjust tie rods, which will require an open ended wrench, and you will want to disconnect sway bars during the alignment and reconnect them later.
Lastly, you will want to put your weight in the driver seat. I used a bunch of weight plates from a weight bench. One alignment shop used bags filled with sand. You could also estimate your weight in spare/used rotors and other heavy car parts.
Unless you fill up your car with just enough fuel to run each session, you do not need to be exact with your weight as most of the time your on track weight will be different. A full tank of fuel in a Miata weighs 72 lbs.
Examine Your Car
This probably should have been earlier on the list, but oh well. Get under the car and figure out what you can adjust and what the adjustments do.
A stock Miata has two eccentric bolts on each corner, for a total of 8. Both bolts are on the lower control arms. Camber is adjusted by moving both bolts inward or outward. Toe is adjusted by moving the bolts in opposite directions. I have not yet attempted caster adjustments thus cannot comment on how they work.
Frustrated with inability to get enough camber, I purchased V8Roadsters control arms. The upper control arms that V8Roadster sells come with an eccentric bolt. As a result, camber is obtained not only by moving the bottom eccentrics against the stationary upper arm, but by moving the upper and lower eccentrics in opposite directions. The extra eccentric bolts in V8Roadsters are, according to them, good for up to 3 degrees of further camber adjustment either way.
I now adjust camber as follows: first rotate the upper eccentric all the way inward, and set both bottom eccentrics in the middle. Adjust bottom eccentrics in or out to get the desired camber. I obtained over 3 degrees of camber easily in this fashion.
Having the additional eccentrics on the upper control arms also makes it easier to adjust toe. As the total camber range is greatly expanded, when I adjust toe I do not worry about whether having desired toe would limit my camber. Given only stock lower control arm eccentrics, it is possible to be camber-limited due to toe.
Besides eccentrics, toe can also be adjusted by moving tie rods in or out of the steering rack.
Put the equivalent of your weight into the driver seat as ballast.
Sway Bar End Links
Disconnect sway bar end links from suspension. You only need to disconnect one end of one end link on each end of the car.
Center Steering Wheel
This is an issue I have been trying to correct ever since I owned the car. My steering wheel was never centered when the car drove straight. I asked multiple shops why this is and never got an answer. Well, this is trivially fixable if you know what you are doing, which apparently many if not most paid professionals do not.
On my car, the right tie rod was fully extended and the car drifted left with the steering wheel straight. To make the car go straight, you extend the right side tie rod and shorten the left side tie rod, but my right side was already at full extension. If you do this after you perform an alignment, the alignment gets screwed up. The second time you align the car however, you fix steering wheel before you begin.
Centering the steering wheel is accomplished by:
- Adjusting both tie rods to be in the middle of their range.
- Performing the alignment using eccentric bolts.
- Fine-tuning toe using the tie rods.
Done in that order, you have the alignment numbers you want and a car that drives straight with the steering wheel straight.
Decide On The Order
With 12 alignment bolts I can set toe first or camber first. I elected to set camber first because it was the measurement that the shops could not set correctly.
I worked on one end of the car at a time. Specifically, I set front camber first, then rear camber.
First, find all of your eccentrics and make note of which way they are facing. Unless you are tweaking an alignment that is close to the specs you want, and you were the one who did it, chances are the eccentrics are positioned pretty much randomly. If so, break them loose and set them all in the middle (that is, with the bolt either on top or on the bottom).
Now is a good time to look at the eccentrics and replace any that are worn. The plate on the nut side is the part that wears first. As you tighten the nuts, you will see that plate moving. If it moves excessively, replace it. What is excessive? Compare to other eccentrics on your car. Rear eccentrics seem to get less wear than fronts so be sure to check those. If you have any new bolts, use them as reference.
The plates are very cheap ($3 each or so at Mazda Motorsports), replace them if you have any doubt. Somehow the entire eccentric assembly is cheaper than just the bolt, so you would want to have a bunch of complete assemblies and a few plates in your spare bin.
OK, with eccentrics in good shape use the outer bolts to adjust camber. If the outer bolts alone are insufficient, use the inner bolts on the same end of the control arm as the outer bolts. As the inner bolts are used for toe, adjusting camber with the outer bolts is preferable.
You will need to set the steering wheel position to straight ahead before tightening anything down, and you will need to check and adjust the steering wheel periodically throughout the process. As you move the suspension, the steering wheel will turn with it.
On a car with 12 eccentrics this is obscenely easy. Simply adjust front and rear inside eccentrics to set the desired toe.
Eccentrics are a cruder adjustment tool than tie rods. When you are close to the desired numbers, you may want to finish front toe adjustment with the tie rods.
Remember to check that the steering wheel is set straight during the adjustment process.
The toe bar gives you toe but not whether front and rear tires are parallel. That you can eyeball. With your eye at the front tires' vertical center line, look back to the rear tires. You should see the same portion of rear wheels on the left and right sides of the car. If your toe is zero, the rear wheel should disappear. Go to the rear of the car and look through the rear wheels at the front.
Look up the specification for track width of your car. Miatas have wider rear track than front which means you will see more of the rear tires from the front of the car than you will of the front ones from the rear of the car.
If you followed the toe tip above, you should have a thrust angle that is pretty close to correct.
I have not set caster yet, because I did not want to spring for turn plates.
However, this page gives a formula for figuring out caster given a specific turn angle. The Longacre camber/caster gauge wants you to turn the steering wheel to a certain turn angle. It would be much easier to turn the steering wheel one full turn in either direction and calculate the caster from that.
It should also be possible to set the caster the same left to right without knowing what it is.
Use white-out to mark the positions of all eccentrics. You want to have a line from the plates to the subframes. Later, check whether the eccentrics moved by looking at whether the lines are unbroken.
Marking the eccentrics before torquing them will inform you if you moved them during the torquing.
The torque specification for alignment bolts appears to be as much as humanly possible ft-lbs. This is definitely true if you intend to drive at Pocono Raceway.
Reconnect Sway Bars
Adjust sway bar end links for the new distances to mounting points and reconnect.