Miata Suspension 102: Alignment

By Loren Williams (reviewed by people with more knowledge than him, proofread by people smarter than him)

This is the second of four articles in this series. In the first article we discussed the basic parts of the Miata suspension and what they do. Hopefully you took the time to look at your car or at least a good shop manual to get a better idea of how those parts function. If you’re completely lost, just come to the next club tech session and ask someone to give you a guided tour.

Talking about the basic parts is pretty easy. Every Miata has the same parts, and they all do the same thing. Simple. And then there’s the matter of how to adjust all those parts… the alignment. This is where things get a little more interesting. You may recall that I mentioned the spring rates that Mazda chose for the Miata were a compromise. Well, so are your alignment settings (and a lot of other things). The best alignment settings to use on your car will depend on how you drive, where you drive, what type of competition you do (if any), other modifications you have made to your car, the tires you use, how long you expect those tires to last, and the phase of the moon.

Where to begin? Before we get into where to set things, a good understanding of what each of the settings are would be helpful. This shouldn’t take too long…

What is Camber?

This is the one you’ve probably heard the most about. That’s because it has a lot to do with good cornering. Camber is the angle that the top of the tire leans away from the center of the car. For our purposes, what we really want is for the top of the tire to lean toward the center of the car. This is called negative camber. Negative camber is good! If camber is negative when the car is pointed forward and at rest (static camber), it will be closer to zero on the outside wheel in a corner. In plain English that means that the contact patch of the tires that most of the car’s weight is on when you are turning will be almost perfectly flat on the pavement. See, I told you it was good!

What is Toe?

You may have heard of this one, too. Toe is the angle that the front of the tire is pointed inward from straightforward. It’s great fun to play with. You might think that zero toe (having the wheels pointed straight forward) would be the way to go to keep the car going straight. Well, not quite. For straight-line stability, a little bit of toe-in is the answer. For quicker steering response, toe-out does the trick. When we get into specifics, you’ll learn that a good Miata alignment typically uses a little of each.

What is Caster?

Not quite as popular to discuss, but still very important. Caster is the angle that the center of the steering axis is tilted forward. Think of the front wheels on a typical shopping cart. The “steering axis” on those wheels is tilted to the rear (negative caster), making it almost effortless to steer a shopping cart, and giving it no inherent desire to roll in a straight line. The opposite example would be a “chopper” style motorcycle with long forks going to the front wheel. The steering axis is tilted WAY back on this bike (positive caster) and it will have the tendency to go straight at the expense of making it a bit harder to turn. The basic effects are exactly the same on your Miata, but there is another side effect due to the design of the Miata’s suspension. Remember that gain in negative camber when your suspension compresses? If you have more caster, you get more of a gain in negative camber under compression. For this reason, you will often see people recommending “maximum attainable positive caster”. More about that later.

That’s it, folks. Those three little adjustments front and rear are all there is to an alignment on a Miata (or any other car).

Factory Alignment Specs

Now that you know what the adjustments are, and have a little understanding of what they do… where do you want to set them??? Let’s start by looking at the factory alignment specs. Where did the factory intend for you to set things?

Front Camber: -0.6 to +1.4 degrees

Front Caster: +3.4 to + 5.4 degrees

Front Toe: -0.05 to +0.35 degrees

Rear Camber: -1.7 to +0.3 degrees

Rear Caster: there is no steering and thus no caster (you knew that, right?)

Rear Toe: -0.05 to +0.35 degrees.

(Note that these are the specs for my ’96, they may vary from year to year, but should be pretty close for all years.)

There ya go. Set your alignment to dead center of those specs and you’ll have a car that will handle adequately for the “typical” driver, not cause undue tire wear for the “typical” driver, and otherwise be fairly safe and predictable. If you never experimented with a “better” alignment, you’d never know the difference. But… if you like to explore the limits of your car’s handling on a regular basis, there is more there for you. Much more. And all it takes is a couple turns of your alignment tech’s wrench.

This would be a good time to mention that alignments from the factory or even from the average local alignment shop could be pretty much ANYWHERE within the factory specs. If you’re serious about handling, ask around and find an alignment shop that will do an alignment to YOUR exact specs without question and with a big ol’ smile on their face. Even if you have a brand new car with 200 miles on it, it will benefit from a good alignment. You’ll be glad you did.

Performance Alignment Specs

So whaddaya do if you want a “performance” alignment? You go to Miata.Net, of course! There you will find the infamous “Miq spec” alignment by Miq Millman. Miq has written a very good article, similar to this one, that has become the starting point for many Miata suspension tweakers, myself included. Here’s what Miq recommends:

Front Caster: +4.7 to +5.5 (what ever the maximum attained is)

Front Camber: -0.6 to –0.8

Front Toe: 1/16” per side, or 1/8” total toe out

Rear Caster: not applicable, there is no adjustment possible

Rear Camber: -1.1

Rear Toe: 1/16” per side, or 1/8” total toe in or zero

If you look closely at the Miq specs compared to the stock specs, you’ll notice that Miq is basically putting you on the performance edge of the factory specs. This is a great place to start for a street-driven car. But you can further refine these specs to meet your own personal driving needs. Let’s dissect the Miq spec and discuss why each spec was chosen and in what way you might want to change it.

Camber Adjustment

Let’s start with a couple quick facts about camber. As mentioned above, negative camber is good.

As evidenced by the Miq spec pushing slightly beyond the factory spec, you really do want a fair amount of negative camber for good handling. Why not just max it out and go with as much as you can get? Well, it depends on your driving habits. If you do a lot of straight-line highway driving, you can have “too much” negative camber and it will show as excessive wear on the inside edges of your tires. However, if you don’t do as much highway driving, and tend to do a lot of hard cornering on the street (not that I would ever advocate such a thing) and/or autocross regularly, you can get away with a lot more negative camber and your tires will wear evenly due to your driving style. If that’s the kind of driver you are, you can get away with up to about –1.8 to –2.0 degrees maximum without uneven tire wear.

Very important rule of thumb about camber here. Unless you’ve done something to change the balance of the car (changed springs and/or swaybar combination to cause the car to over-or-understeer) you will want to maintain very near a half degree more camber in the rear than in the front. So, if you’re planning to max out the rear camber at –2.0, you’ll want to set the front at –1.5. Maintain that camber differential and you’ll be a happy neutral-steering camper.

Camber adjustment is made by turning the forward adjustment bolt on each of the lower control arms. Adjusting camber will effect caster and toe settings.

Front Caster Adjustment

Factory spec is about +3.4 to +5.4. Miq and others recommend either about 5.5 or “as much as you can get”. These guys are overlooking two things: 1) It is possible for the caster to be set at +7 degrees or more! 2) Too much caster is not good for a car without power steering.

My recommendation is to stay within or at least very near the factory spec. More caster means more negative camber in a turn… but it also means more steering effort. The steering effort isn’t such a big deal with power steering, but if you happen to have a car with manual steering it simply can’t be overlooked. Less caster will give the steering a light, easy feel. More caster makes the steering feel heavy and hard to turn. If you have manual steering, you’ll be happier if you keep the caster set below 4.0 degrees. With power steering, take it on up to 5.5, but I’m not so sure about “more is better” beyond that.

Caster adjustment is made by turning the aft adjustment bolt on the front lower control arms. Adjusting caster will effect the toe setting.

Front Toe Adjustment

As previously mentioned, toe in will make the car feel more stable and on-center, toe-out will make the car more eager to turn. We like our Miatas to turn sharply, so a little bit of toe out is good. How much is a matter of opinion and driving style. Most people who do mostly street driving will stick with 1/16-1/8” per side (that equates to about -0.05 to -0.10 degrees). If you do a lot of autocrossing, you might want a little more toe out for even quicker steering response. But be aware that more toe out WILL cause greater tire wear. (one of my technical advisors told me to reiterate that point) Be aware that more toe out WILL cause greater tire wear.

Front toe is the one alignment setting that is truly simple to adjust. If you’re adventurous, you can actually play with this one yourself. Just loosen the locknut on the tie-rod and adjust the tie-rod as needed. If you are going to mess with it, be sure to mark where things are set before you begin and be sure to adjust both sides by the same amount. A half-turn will make a noticeable difference. This adjustment has no effect on other adjustments.

Rear Toe Adjustment

All the rules we talked about for front toe also apply to rear toe. There is the added element of the rear of the car being the end that we really don’t like to lose control of, however! For this reason, most sane people don’t opt for toe out in the rear. In fact, because the suspension bushings allow the toe setting to move outward just a bit under acceleration, a little bit of toe in is preferred. If you go with the Miq spec of 1/16” toe in, your rear toe will NEVER go positive, and that’s a good thing. We all like nice quick steering response, but we also like predictability. If you’re setting a car up for either track use or highway driving at imprudent speeds (nope, I’d never advocate that, either), you may even want a little more toe in. Going up to 1/8” (0.10 degrees) toe in will make the car much more stable at speed. But… more than that will cause problems like annoying wheelspin when you get on it from a stop.

Rear toe is adjusted just like front caster, with the aft adjustment bolt on the lower control arm. This adjustment has no effect on any other adjustments.

The next article will get into some simple suspension modifications. The real fun begins there!