5.0 Mustang & Super FordsHow To Chassis Suspension
Front-End Alignments - Alignment Refinement
Getting The Most From Your Alignment Dollars-And Your Front End
Setting a proper alignment assumes the Mustang can hold on to that alignment. Tired, old rubber bushings on a 20-year-old Fox could be a problem. If you're becoming serious about handling with an older project car, make sure the suspension can take it.
Part of the Mustang ownership experience is staring down at a $190 front tire that's in perfect shape except for the outer inch where the rubber is ground off to the steel cord. After a couple sets of such tires, this becomes powerfully tiresome-enough to motivate even dedicated engine men into some interest in front-end alignment.
Admittedly, for most Mustangers, the topic of front-end alignment has the compelling draw of a wastewater-treatment facility bond issue-necessary, but not the sort of thing you look forward to reading up on at night. At least not until you've thrown away a few $190 tires that were still wearing almost all their rubber.
Notice we said "most" enthusiasts. You corner-carvers know there is a growing trend toward chassis performance, and you also know a good front-end alignment is the first, and most affordable, step toward proper tire wear and enhanced cornering.
Let's begin by saying there is no magic set of alignment numbers that works for all Mustangs and, more importantly, Mustang drivers. Just as there is no single perfect camshaft, there is no single perfect alignment. Where and how you drive makes a difference in the amount of caster, camber, and toe your Ford needs.
Just as interesting, receiving a custom alignment is hardly the norm. All the large chain shops, big tire discounters, national retailers, and many a local shop bow slavishly to published alignment specs. Want something different? You'll only get an argument from them. For anything else, you need to find a local shop used to dealing with specialty cars. Ask your local speed shop or performance-tire-and-wheel center for directions. They'll know of a shop and maybe even a specific technician who will work with you to get what you want. And, yeah, expect to pay a bit more for the one-on-one treatment.
Front-wheel alignment and associated suspension and steering geometry use many specialized terms. We'll stick to the three that matter-and are adjustable-during a typical alignment. They are caster, camber, and toe.
Caster is typically the most difficult parameter to visualize. It is the angle between the ground and a line drawn between the upper strut mounting point and the lower ball joint when looking at the car from the side. Oversimplified, it is how far the top of the strut is laid back from vertical. This is positive caster (the only kind we'll encounter); negative caster would be if the top of the strut was closer to the headlights than the firewall.
Caster has several effects. Similar to the caster on a shopping cart, it gives the steering a self-centering energy because the contact patch of the tire is behind the tire's steering pivot point. Thus, increased positive caster increases steering effort.
Increased positive caster also causes a correspondingly larger change in ride height when steering (which also increases steering effort). You can see this when the car is stationary and the steering is turned lock-to-lock. The front fenders alternately rise and fall as the wheels turn. By itself, this is relatively unimportant, but it helps greatly in visualizing caster's most important characteristic-camber gain while steering.
Camber, or lack of it, is what grinds away Mustang tires. Defined, camber is how much the top of the tire tilts when viewed from the front or rear. Get in front of your parked Mustang and sight down the side. If the top of the front tires tilt outward, then that is positive camber. Let's hope you don't see any of that. Negative camber is when the top of the tire tilts in, toward the engine.
Now, the goal is always to present the tire tread flat to the ground for maximum traction and minimum tire wear, but doing that calls for different amounts of camber depending on what the car is doing and how hard it is doing it. Because the tires spend so much time going straight, it is necessary to start with more or less negative camber in the normal, straight-and-level position or rapid tire wear will occur. The other important condition is cornering, when the loads on the tire are high. After that, all sorts of suspension and steering geometries come into play, and picking the right static camber-the one set in the alignment bay-becomes something of an art.
In practical terms, just how much negative camber to dial in will depend on how much aggressive cornering you do.
Easiest to discuss is toe. Imagine looking down on your car from directly overhead. If the front tires both point perfectly straight, there is 0 toe. If the front of the tires points in, that's toe-in. Toe-out is where the leading edge angles out. Clearly, 0 toe is desirable, as it doesn't drag the tires across the pavement in a speed-killing, tire-wearing scrub.
What you actually set the toe to on the alignment rack depends on a few things. First, there is often a bit of slop in the steering system. A hint of either toe-in or toe-out will load the steering slightly, enough to take up this tiny bit of play.
Toe-in offsets the tire's natural drag (caused by the suspension geometry) to toe-out. Thus, just a hint of toe-in on the alignment rack can give true 0 toe going down the road. Adding more toe-in adds stability to the steering, and makes the steering a hair less responsive to turning into a corner because the tires are already pointed just a hair out of a corner.
As you'd guess, toeing out the tires makes the steering more eager to corner turn-in. But it also makes the steering ready to wander, and requires constant steering adjustments while trying to drive straight down the road. Hence you'll always get some toe-in from Ford and the alignment shop unless you specify differently. Hint: You'll find toe-out feels more like "unstable."
For much-needed assistance with the numbers for this article, we spoke to several shops that commonly deal with Mustang front ends. These included Maximum Motorsports and Steeda. Their experience shows there are differences depending on what year Mustang you are talking about. Up to 1993 things are basically the same. In 1994 Ford improved the spindle (among other things) on the then-new SN-95 chassis cars, which had an alignment effect. Later still with the '99 cars, more changes were made, although the jump between the Fox and SN-95 cars in 1994 remains the biggest difference. There are also differences between a stock suspension, where maybe a set of caster/camber plates, lowering springs, and shocks have been installed, and a performance suspension, which includes a reworked K-member, camber plates, non-rag-joint steering shaft, stiff bushings, and so on.
On The Rack
OK, your car's on the alignment rack. What sort of tune do you want on the suspension? What a Mustang needs is mainly more negative camber while cornering, which means a bit of static negative camber and considerably more positive caster.
Caster-With stock alignment settings, as you steer the front end, the front tires gain positive camber. This unwanted effect is especially true of '93-and-earlier cars, which offer a modest degree or so of caster.
Increase positive caster and retest the camber with the tires turned 20 degrees (the industry standard and nearly full lock on a Fox car), and you'll find the cross-over point is 4 degrees of positive caster. At 4 degrees or less caster you'll gain positive camber while steering. About 4 degrees or more of caster and negative camber is gained while steering. The most desirable point is to have gained 1 degree of negative camber at 20 degrees of steering. This is often around 6-8 degrees of positive caster, but that can be too much for a typical daily driver street car that doesn't see much hard cornering. When that happens, the inside edge of the front tires wears off.
Garden-variety, daily driver Fox cars do best with 3-4 degrees of positive caster. For one thing, this is the physical limit of adjustment where either the upper strut shaft runs into the edge of the hole in the inner fender, or the stock camber plate runs out of adjustment range. This is the source of the old pit-rail advice to simply pull the struts back to the limit of their travel. It's basically true on Fox cars.
SN-95 Caster-The '94-and-later Mustangs come with around 3.6 degrees positive caster (Ford allows a range of 2.85-4.35 degrees), so they can be fairly close to the 4-degree crossover point when stock. Daily drivers should be at 4 or more degrees, with 6 or 6.5 degrees the likely optimum.
According to Maximum Motorsports, you can pull the top of the strut back to 8 or 9 degrees on SN-95 cars, but the company cautions that at 7 degrees at the most, you'll have induced enough geometry changes to cause increased bumpsteer. So, you don't want to pull these struts all the way back-somewhere around half the available plate adjustment is about it.
Also, don't get torqued out of shape if the caster varies a bit from side to side. Caster is ultimately something of an approximation as measured on the alignment rack, and responds to many variables. Back the car off the alignment rack and drive it back on, and you'll find the caster has changed slightly (probably due to a slight change in ride height). Don't obsess over it.
Camber-Radial tires prefer approximately 1 degree of negative camber, simply because of their carcass construction. Furthermore, Mustang suspension geometry gives positive camber as the body rolls over while cornering, so you'd think well over 1 degree of negative camber would be ideal.
The reality is, 31/44 degree of negative camber is about maximum on a typical Mustang street driver. Any more tilts the tire enough that the inner edge of the tire wears out when driving straight ahead. For this reason, stock Mustangs are typically set up with 11/42-31/44 degree of negative camber.
How aggressively a Mustang is driven makes a huge difference, too. A steady diet of freeways or straight farm roads calls for the least camber, about 1/2 degree negative. Hard-driven, canyon-country steeds may wear their tires most evenly at a full degree negative, and we've heard of some beady-eyed g-junkies that did best with almost 2 degrees of negative camber on the street. Mind you, these tires wore evenly, but that's not to say they wore a long time!
Maximum Motorsports recom-mends 1 1/4 degrees of negative camberas a starting point for its hotter street customers, but cautions tire wear must be watched closely at this setting and the camber subsequently adjusted to suit tire wear.
Road race cars often use around 2 degrees negative camber; autocrossers are the most radical with 2-3 degrees of inward tilt.
Interestingly, some of the last Fox cars, the '90-'93 machines, came from Ford with more than 1 1/2 degrees of negative camber at stock ride height. A real novelty among Foxes, these cars have more positive caster as well, and can possibly have too much negative camber. Watch for inner tire wear, and expect to add a caster/camber plate in order to reach a more even-wearing 1/2-3/4-degree negative camber.
You can accept 1/8 degree of variance in camber settings. Ride height changes camber, for example, so driving around the block will change the camber just a hair. Unlike caster or toe, camber falls in a range of more acceptable readings, not a laser-precise readout.
Toe-Ford doesn't allow any toe-out. Zero to toed-in a hair, say 1/8 inch, is what Ford allows, and this is good for a typical street car. Try to stay away from 0 toe, as due to play in the steering the wheels tend to hunt some.
Road-race, open-track, and especially autocross Mustangs can run some toe-out, up to 1/8 inch per side. This will require constant steering corrections and can make the car nervous, so you may want just a hair of toe-in for an endurance road race where driver fatigue is a concern. Otherwise, the more rapid turn-in is welcome.
It's good to point out that prepared race cars have little play in their suspensions and steering due to urethane or spherical rod ends, non-rag-joint steering shafts, and the like. This makes them more precise, and it can also give them more hair-trigger feeling when toed out. At least their high-precision chassis also allows quick, almost unconscious, steering corrections. The same is hardly true on a stock Mustang, where the slightly vague and numb steering can make toe-out a real white-knuckle affair.
Probably the main point to remember with front-end alignment is to simply have it done. New tires have traditionally been a call for alignment, and that's still a good rule. Bushing replacements, any time the K-member is moved (a rarity), upper strut movement, or accidents, are also cause to visit the rack. Luckily, dropping the spindles from the lower struts for shock or spring work does not affect alignment, though it seems it would. If in doubt, check your tire wear. It's how your Mustang tells you what it needs.
Dan Carlson at Steeda has seen many Mustangs cross his laser-collimated alignment rack, giving him the experience to say the alignment specs he dials into a car depend on the customer. The two variables are what the customer does with the car, and somewhat with the level of equipment (caster/camber plates or not) on the car.
Practically speaking, however, he finds that dialing in as much caster as is physically possible is desirable. Caster "makes it much easier to get the best of both worlds," Dan says, referring to the need for 3/4 degree of camber for freeway driving and 3 degrees of camber when corner carving.
Like everyone else, Dan has found setting camber is the big question, but about 3/4 degree negative is good for freeway commuters and 1 1/2 degrees a good starting point for the cornering crowd. "Some race guys who are pretty competent will experiment," Dan says, "and we encourage them," but in the end tire wear is the best indicator of when the camber is properly set.
Toe-in is 3/32 at Steeda, save for the wildest autocrossers perhaps. They might try some toe-out.
Dan pointed out that good springs, with more control than taller, softer factory ones, are beneficial in controlling the car and arriving at more precise alignment specs. Wallowing around on soft springs means the suspension moves through such large arcs that the camber is moving all over the place. So, as you add handling suspension parts, you can also dial in a more responsive front-end alignment.
Pulling To One Side
Out-of-spec caster or camber can cause a pull in the steering, but typically the tires cause the problem. When misaligned, the belts in radial tires will cause a pull-swapping the front tires left to right typically cures the condition.
In fact, most alignment shops will give 1/4-1/2 degree more positive caster on the driver side to account for road crown. This is because a car will pull to the side with less positive caster. If you drive on mainly flat roads, you can dispense with this.
Raking the car-typically by lowering the front-affects caster because it rotates the top of the strut closer to vertical. So, lowering the front lessens caster, while lowering the rear gains caster. This is important on Mustangs with aftermarket coilover shocks that have easily adjustable ride height. For low-speed autocrossing, such cars can be set a bit rear low for snappy front-end performance. Higher-speed road racers tend to set the front end just a hair lower than the rear to reduce air from packing under the car and lifting the nose at high speeds.