Rear End Alignment - String Me Along

A common misconception among new racers is they absolutely must have every new gadget and geegaw that comes down the pipe or else they will never win a race again. Truthfully, there are some very handy and innovative tools out there for racers with the potential to save both time and headaches. But if you don’t have a complete understanding of what you are trying to do, you are far more likely to set yourself up for a lot of confusion and frustration.

That’s why Circle Track always recommends the KISS principle (Keep It Simple Stupid) when it comes to racers still trying to learn their way in the sport. By simplifying things down to their core elements you get a better understanding of what’s going on. When we set out to do a basic how-to on making sure your rear end is straight, we went directly to the shop of race car builder Gene Leicht. Leicht’s forte is chassis for asphalt Late Models, and his cars have won more big-money races than he can count. His philosophy when it comes to building cars is—you guessed it—simplicity eliminates mistakes.

“At the Late Model level,” he explains, “if you give a guy too many options he’s likely to tune himself right out of the race. When he was alive, Banjo Matthews (a Winston Cup car builder) had his shop nearby. He told me if you build it right, you don’t need a bunch of adjustments.” While Leicht’s shop has everything he needs to build fast cars, no one is going to mistake it for an extravagant Winston Cup outfit. Even though he could easily justify an expensive laser-sighted instrument to check the geometry on his cars, Leicht still does it the old-fashioned way: with a tape measure and some string.

“Every car that comes out of here gets strung,” he explains. “There are more expensive ways to do it, but I don’t see any reason. Stringing a car is easy, cheap and tells you just about everything you need to know.”

You can completely set up a car by stringing it, but we will concentrate on making sure your rearend is straight. Leicht’s method is probably the most common and bases everything off the car’s framerails. The grocery list required is simple: two lengths of stretchable twine, four jackstands or any heavy moveable object to tie to and a tape measure.

First, run a length of stretchable twine alongside both sides of the car and extend beyond both bumpers. These are your reference strings. Tie the strings to jackstands or some other heavy—but moveable—object and pull them apart so the twine is off the shop floor and reasonably level. Use your tape measure to run the twine a uniform distance from the framerails (Leicht uses 12 inches because it allows him some working distance yet isn’t too far from the sides of the car).

It is crucial that you measure against the framerails and not support struts, brackets or some other piece of metal under the car. It doesn’t matter if you are racing a hand-built tubular chassis or the frame from a ’77 Monte Carlo, if the car is in good shape the framerails are likely parallel. The first time you try this, put the car on jackstands and identify points to measure to the front and back on the outside of both framerails. Mark them so you can measure again later.

On passenger-car frames, good reference points are already there for you. “No matter what type of car it is, you likely will find some squaring points somewhere underneath that’s the same on both sides,” Leicht explains. “Leafspring mounting points are usually pretty square, as are the pivot points on the front end for the ball joints. When a car is built they use marking holes or notches to make sure when they are building it they get everything square; those are pretty good reference points.”

Once you have your lines strung parallel to both framerails, it’s time to make sure they are parallel with each other. Simply measure the distance between the strings in front of and in back of the car. If the numbers match, your framerails are parallel. If they don’t, it’s time to figure out why not.

“If those numbers are off any, it’s not the end of the world,” Leicht says. “Maybe there’s a dent on the outside of the tubing. Your lines have to be parallel to string a car properly, but your framerails don’t have to be in order to have a fast car. If you are an eighth of an inch off, then you can tack weld an 1/8-inch piece of material to that spot to even it up. Just make sure your strings are parallel with the car. As long as you get all your wheels pointed in the same direction, your steering working right and your geometry worked out, it’s going to work. The car doesn’t care how.”

Now that you have your reference strings parallel to each other and the car as well as a uniform distance off the ground, it’s time to get started. Leicht makes sure his car is sitting on rims that haven’t been involved in a wreck and he knows aren’t bent. He picks two points on opposite sides of one of the rear wheels that is equal to the height of the reference string and measures the distance between the wheel and the string. If your measurements on both sides of the wheel are equal, then that wheel is parallel with the direction of the car. Unless you are moving the rearend for handling purposes (which we will talk about), all the wheels need to be parallel with the direction of the car so the car won’t be scrubbing off horsepower or crabwalking.

Next, Leicht moves to the opposite wheel and repeats the process.

“Make sure you measure from the string to the rim and not the sidewall of the tire, which could have fallout and be inconsistent,” he cautions.

If the two measurements on this side are equal, then this wheel is also rolling in line with the car and the rearend is straight. If the four measurements are all equal, then the rearend is centered underneath the car. Total the distance between both tires and their respective reference strings and then subtract that total from the distance between your two reference strings to find the track width of the rear end.

Think you have it? Good, now let’s take it to the next step. Leicht’s numbers sometimes are purposely unequal because he occasionally mounts a rearend on an angle to help the car turn. By pivoting the rearend so the wheelbase on the left side of the car is shorter than on the right, Leicht can make the rear end of the car swing out slightly when the driver turns the car to the left, making the car feel looser, or easier to turn. This means that on the left side of the car Leicht’s measurement from the rim to the reference string at the back of the wheel will be shorter than the same measurement at the front of the wheel. The measurements will be equal but reversed on the right side of the car.

Leicht normally limits the difference in distance to 1/16 of an inch. The front of the car is a little more difficult because steering adds a new variable to the mix. First Leicht centers his steering box by making sure the center of the bolt in the pitman arm is the same distance to the nearby framerail as the main bolt in the steering box. He then adjusts the front tires using the tie rods. By measuring the leading edge of the rim versus the rear, Leicht can dial in exactly the amount of toe-in or -out he desires and can get good repeatability race after race, car after car.

Not bad for two pieces of string and a tape measure, huh?