Wheel Alignment Tool

A string alignment is how motorsport set cars up long before racks existed, and a string wheel alignment tool is still how most paddocks do it between sessions.

Two frames, two strings and a ruler, and the accuracy comes from the setup rather than the equipment.

What a String Alignment Measures

Two frames sit ahead of and behind the car, each carrying a string that runs down one side at hub height.

Those two strings form a rectangle around the car. Measuring from each wheel rim to the string beside it gives the toe at that corner.

Because each side is measured independently against its own string, you get individual toe at all four wheels rather than only the total across an axle.

That is the main advantage over a simple toe alignment tool, which measures across the car and tells you the total without showing how it is split between the two wheels.

Camber needs a separate gauge used alongside, and caster is derived rather than measured directly. Toe is what the strings do, and toe is the setting that changes most often.

Squaring the Box to the Car

This is the step everything else depends on, and it is where a string alignment goes wrong.

The rectangle has to be parallel to the car's centerline, not to the wheels, the garage wall or anything else.

Set the strings at hub center height on both sides. Measuring at a different height introduces camber into a toe reading and gives numbers that look plausible and are not.

Then equalize the offsets measured on each side. Measure from the hub center to the string at the front and at the rear on one side, and adjust until those two figures match. Repeat the same process on the other side.

The two sides do not have to be the same distance from the car, only consistent front to rear on each side. That is what makes the strings parallel to the centerline rather than parallel to each other at an angle.

Check the equalization again after any adjustment, since moving one frame moves both strings on that end.

Taking a Toe Reading

With the box square, the measurement itself is straightforward.

Measure from the string to the front edge of the wheel rim, then to the rear edge of the same rim, at the same height on both.

If the front measurement is smaller, that wheel is toed in. If it is larger, the wheel is toed out. The difference between the two is the toe at that wheel.

Use the inner lip of the rim rather than the tire sidewall. Sidewalls bulge, vary with pressure and are not a straight reference.

Take each reading twice before you move on. Strings move, rulers sit slightly differently, and a repeated figure is one you can trust.

Record all four corners before adjusting anything, since changing one wheel moves the car's attitude and affects what you measure next.

Turning Measurements Into Settings

The number you take off the ruler needs converting to be useful.

Toe measured as a difference between front and rear rim edges is a linear figure, and specifications are usually given either in the same linear form or in degrees.

The conversion depends on the rim diameter you measured across, since the same angular toe produces a larger linear difference on a bigger wheel.

Measure at the rim rather than the tire for exactly that reason. The rim diameter is a known figure and the tire's outer diameter is not.

Where a specification is given in degrees and you want to work in millimeters, work out the linear equivalent once for your wheel size and use it as a reference.

Adjust the tie rods in small increments each time. Half a turn on a tie rod moves toe further than most people expect, and overshooting means working back.

What Comes in a String Alignment Kit

The hardware is simple and each part has a job.

Two frames or bars sit ahead of and behind the car, wide enough to place the strings outboard of the wheels and adjustable so they can be positioned for different track widths.

The strings themselves need to be non stretch, since anything elastic sags differently at each end and gives a reference that is not straight.

A ruler or measuring gauge reads the distance from string to rim. A rigid rule with a clear scale beats a tape measure, which flexes and is hard to hold square.

Between them those parts give a repeatable reference around the car, and the accuracy comes from how carefully they are set rather than from what they cost.

Supports or stands hold the frames at hub height, and anything that lets the height be set precisely and locked is worth having over something improvised.

Adding Camber to the Picture

Strings handle toe, and most people want camber at the same time.

A camber gauge sits against the wheel face or the hub and reads the angle from vertical. Digital versions give a number directly, while bubble types are read against a scale.

Measuring against the wheel face assumes the rim is true and undamaged, so check for buckling before trusting a reading taken that way.

Take camber readings with the car settled in the same position used for the toe measurement, since both change with ride height.

Camber and toe interact on most suspensions, so adjusting one usually moves the other. Measure both, adjust, then measure both again rather than assuming one change stayed isolated.

That iteration is normal rather than a sign something is wrong, and it is why recording the numbers as you go saves time.

Checking Thrust Angle

The strings give you something a toe gauge cannot.

Thrust angle is the direction the rear axle points relative to the car's centerline, and it is what makes a car travel slightly crabbed with the steering wheel off center.

With the box squared to the centerline, comparing the rear toe readings left and right shows whether the rear axle is square. Equal readings mean it is, and a consistent difference means the thrust angle is out.

That matters because no amount of front toe adjustment corrects it. A car with a thrust angle problem needs the rear addressed, and on a live axle that usually means locating components rather than settings.

Being able to see it before paying for a rack visit is one of the more useful things the setup does.

String, Laser or a Rack

Three approaches exist and they are not interchangeable.

A string alignment kit measures toe precisely and relies on careful setup. As a car wheel alignment tool it is the cheapest route to numbers you can trust. It costs less than a single rack visit, it works anywhere flat, and it takes longer the first few times.

A laser wheel alignment tool works on similar principles with a projected line instead of string. Setup is quicker and the equipment is more fragile and more expensive.

A four post rack measures everything at once, including camber, caster, thrust angle and individual wheel positions, and it does it in minutes. For a car that needs a full alignment after accident damage or major work, that is the right tool.

The string setup is for the car that gets adjusted often. Different tire, different circuit, different driver, or a check after a session, where paying for a rack each time would stop the adjustment happening at all.

Surface, Pressures and Repeatability

The variables that affect readings are worth controlling rather than fighting.

Level ground is the first requirement of the three. A perfectly level floor is ideal and consistency matters more, since the same patch of concrete used every time gives comparable results even if it slopes slightly.

Tire pressures change rolling radius and therefore ride height, so set them before measuring and set them the same way every time.

Fuel level and anything in the car change corner weights. Measuring with a full tank and an empty one gives different answers on a lowered car.

Roll the car forward and back a car length after any adjustment rather than lifting it. That lets the suspension settle into its natural position instead of holding whatever the jack left it in.

Keep a record of the procedure you used along with the numbers, since a figure taken a different way is not comparable to the last one.

Who It Suits

Worth being honest about who gets value from this.

A track car being adjusted between events gets the most. Toe is the setting most often changed, and a rack visit per adjustment is neither practical nor affordable.

A project car being built benefits, since a DIY wheel alignment that gets toe roughly right before driving to a shop avoids destroying a set of tires on the way.

Anyone who has fitted alignment correction hardware gets value from being able to verify the result rather than trusting a printout.

A daily driver aligned once a year does not need a wheel alignment DIY setup at all. The rack visit is cheaper and faster for that use.

Find Wheel Alignment Tools

Doing your own bushings too? The bushing press kit sits next to this tool in our workshop tools lineup.

Browse the string wheel alignment kit and the rest of the wheel alignment tool kit range. Set it up carefully the first time, record the procedure you used, and the readings afterward are as reliable as anything a rack will give you for toe.