Wheel Stringing - Because String Doesn't Lie

The process of stringing a car really hasn't changed since guys like Richard Petty and Cale Yarborough were racking up Winston Cup championships back in the day. That's because it works. Yes, there are fancy systems available to do the job, complete with lasers and CNC-etched calipers. And yes, they do work, but unless you are setting up a half-dozen cars a week the cost often isn't worth the benefit.

That's why many racers still rely on a roll of string, four jackstands, and measuring tape when setting up their race cars. The process of stringing a car is straightforward, relatively efficient, and-probably best of all-you know that when the string is pulled tight it's always straight.

The greatest difficulty with stringing a car is establishing what "straight" is. For example, many racers string their cars off the framerails, but if a rail bends in a wreck or the entire frame is knocked out of line, you can string the car all day long and not get the wheels straight. You could string your car based off the driver's seat, but that's hardly realistic.

Instead, consider using the trailing arm crossmember as your starting point. On most cars, the trailing arm crossmember is the steel tube that runs between the framerails, and the rear suspension connects to it. Almost every chassis builder in the country begins a new chassis by placing the trailing arm crossmember in the chassis jig. Everything else on the chassis, framerails included, is based on the location of this piece of steel.

Begin by using the trailing arm crossmember to square the rear end. You may prefer to race with a little bit of angle in the rear end to make the car more stable, but the car must be squared up in order to string it properly. After you are finished, you can put the preferred pitch back in the rear end. Also, the car should be off the ground because you need to get underneath it. Make sure the wheels are sitting on the stands (which, in turn, are sitting on level floor in your race shop) to properly simulate ride height; you cannot simply put jackstands underneath the framerails.

To square the rear end you will need four plumb bobs, a long straightedge, a tape measure (two is preferable), and tape. Suspend two plumb bobs on string using tape. Be sure to suspend them from the same side of the crossmember (front or back) and to the right and left sides of the crossmember as far outboard as you can comfortably get. Make sure they are extended until they are nearly touching the floor. Once the plumb bobs are perfectly still, line one edge of your straightedge underneath the plumb bobs. This replicates the line of the crossmember on the floor.

Next, secure the other two plumb bobs to the rear end. Like the crossmember, the string can be attached to either the front or the rear of the housing as long as it is consistent. And again, place them as far outboard as possible, making sure nothing gets in the way. The string should be attached to the housing itself.

Using measuring tape, measure from the straightedge to the tips of the plumb bobs hanging from the rear axle housing. Avoid nudging the straightedge out of position. Also, make sure your tapes aren't running at angles, as they need to be perpendicular to the straightedge. If both measurements are the same, you can be confident that the rear end is squared to the trailing arm crossmember. If they aren't the same, adjust the suspension until they are. The adjustments should be built into a tube-frame car, but if you are racing an OEM suspension you may need creativity to align the rear end. One of the primary problems with stock suspensions is that worn bushings and bent trailing arms throw off alignment. Check for those issues first.

Now that the rear axles are established as the baseline, the direction and location of the front wheels can be based off the rear wheels. The next task is to center the steering system and lock it down so that it cannot move.

Lining up the front wheels is futile if the steering wheel isn't centered. If you race a car with a rack-and-pinion system, all you have to do is count the turns of the steering wheel from lock to lock and then find the approximate center. But if you are racing a car with a more traditional drag-link system, finding the center is more involved.

To do this, simply take a set of cross measurements and adjust the system until those two measurements are equal. First, measure from the center of the pitman arm pivot to the center of the drag-link pivot on the opposite side. Then, measure from the center of the idler arm pivot to the center of the opposite drag-link pivot. If these measurements are equal, the steering rack is centered. If they aren't, turn the wheel in small increments until they are. Most steering boxes have a flat spot built into them at the center point, which you may be able to feel in the steering wheel. Once you have found the center, lock down the wheel so that it cannot be bumped accidentally and knocked out of line. The most common way to do this is with two locking pliers. Lock them onto the steering shaft with the handle against a framerail. They should be set so that one keeps the wheel from turning left while the other keeps the wheel from turning right.