When it’s not a post about time attack, you’ll notice most of this site is dedicated to suspension related things. That should make sense given that this site was started to counter the “hellaflush” trend of ruining suspension. In previous post about bushings and coilovers and ride heights, I mentioned alignment quite a bit, but realize I’ve never actually talked much about it in detail, so here goes.
Simply put, the alignment is what direction the wheels and tires are pointed. Straight, right?
Well, sure, that is the general idea, we definitely want all our wheels/tires to be pointed in about the same direction, usually straight ahead relative to the chassis. There are a few things we are usually concerned about- minimizing tire wear and optimizing the contact patch and traction.
Toe and camber are two alignment terms you’ve probably heard, and while they aren’t the only parts to an alignment (we’ll get to some other ones later) they are definitely the most important. Toe is the direction the wheels are pointed relative to the car and zero toe means the wheels are pointed exactly straight. Camber is the angle of the wheel and tire to the ground, and zero camber means the tire is standing straight up. So, then, having zero toe, and zero camber all around means all the tires are rolling straight and the tread is evenly loaded. That should do it, right, I mean, why would you not want that? If the camber isn’t zero, one edge of the tire is loaded more heavily, and will wear faster than the other. If the toe isn’t zero, the tires will be scrubbing slightly as you drive down the road. Either one means more tire wear.
If all you wanted to do is drive down straight highways all the time, then yes, zero camber and toe would be ideal. But sometimes you drive around corners.
When you turn the car, the suspension moves, the body rolls, and the tires flex. What this means is that your contact patch, which was flat on the ground, has changed. Now, instead of using the whole tread of the tire to generate cornering force, only the outside edge and maybe some of the sidewall is doing the work. Clearly, that is not ideal.
This is where camber comes in (and suspension design). Leaning the wheel and tire in a bit, giving it negative camber, will get the tire closer to flat in a corner and put more of the tread in even contact with the ground, which increases traction. In nearly all cases, it’s good to start with a bit of negative camber. How much depends on a lot of things. Most important, what the car is being used for. A track or autocross car is obviously going to require a different alignment than a daily driver. Additionally, the tires and suspension are other big factors.
So where do you start? Well, first take a look at the tires. Is the tread worn evenly all the way across, or does one side seem worn down more or faded? If one side is obviously worn more than the other then the camber should probably be adjusted and the toe should be checked. You can get it in the right ballpark based on the type of driving done and keep an eye on the tires from there. For commuting and highway driving, minimal camber is needed. Driving on a race track with sticky tires, probably quite a bit will work best. Fun driving in canyons, somewhere in between. How much is minimal? I’d say -0.5 to -1 degrees. How much is a lot? Over -3, up to -4.
There is, of course, a better way to figure this out, especially for performance/track driving where optimizing grip is most important, and that is the tire temperature probe. A tire temp probe and a notebook are two of the most important tools you can bring to a track day. By measuring the temperature across all the tires, you can find out how the alignment, tire pressures, and suspension setup should be changed. Hotter on the outside of the tread for example means that corner probably needs more negative camber. If the front or rear tires are significantly hotter that might mean a change to the springs or swaybars is needed.
I think that gets through the basics of camber adjustment, so what about toe, and other stuff like caster? Toe, as we mentioned, is the way the wheels are pointed relative to the car. In most cases, this should be zero, so all the wheels are straight, but there are some cases when changing it can be useful. A little bit of toe in, where the fronts of the tires are closer together than the rear, tends to add stability in a straight line. That might be desirable on a drag racer or land speed type car. Toe out on the other hand does the opposite, and will make a car kind of twitchy and willing to change direction. That could help in an autocross situation where speeds aren’t really high but changing directions quickly is important. Another thing is that having camber will result in a thurst force- the tire will want to go the way it is leaned. Counteracting this with some toe can result in reduced tire wear, especially with a lot of camber.
In addition to toe and camber, there are some other alignment things you might have heard of- Caster, and a related suspension angle- steering axis inclination. These two only apply to the front suspension and have to do with the steering geometry. The main purpose of caster is to add a self-centering force to the steering. It does that by “leaning the suspension back” so that as you steer, the tire leans over a bit as well, which means the axis the tire steers about is in front of the center of the contact patch. That lean has another benefit, and that is that the tire leans a bit as you steer as well. So when cornering, you get a little bit of extra camber outside.
Compared to caster, steering axis inclination would be the angle of the steering looking from the front. SAI is important mostly because of something called scrub radius. A zero scrub radius means that the center of the tread is the pivot point when steering. Zero scrub, or close to it, is desirable so that bumps and uneven road surfaces aren’t exerting a steering force on the tires. Caster and SAI are generally not adjustable on a stock car, but can be changed to a slight degree with aftermarket parts like offset bushings and adjustable arms and top mounts. Generally speaking, more positive caster is a good thing, and we want to minimize SAI while maintaining close to zero scrub. If you’re paying attention, you might realize that wheel offset is important here, since it moves the center of the tire and changes the scrub radius.
What does it all mean? Well, a car’s suspension is a complex system, and if you want the best performance,and getting the alignment right is a very important part of it all. You can’t just throw on a set of $800 coilovers and bring it to firestone for a lifetime alignment and call it good.
The other thing you should know is that the alignment changes when the suspension moves, and also when the ride height changes. Most cars have fairly limited adjustment, so it’s not uncommon to need additional parts to get where you want to be- camber bolts, top mounts, adjustable links, etc. What;s needed depends on the car and suspension layout.
All this means is that it’s really important to find a shop or alignment/suspension guy that is familiar with your specific car if you want to start changing these things.