Straightness

No amount of balancing will matter if a wheel rolls like an egg. Chris Sage at The Wheelsmith noted a few things that prevent a wheel from rolling true. "It's a good idea to check all wheels, and especially old ones, for runout," he begins. "I like to build wheels with no more than 0.015-inch radial and lateral runout but that's so we know a wheel won't ever be the cause of any problems." He even noted that a wheel with 0.030-inch runout will likely work just fine. "Until the '70s or '80s the OEMs considered 0.055-inch runout acceptable."

Because most wheels center on the lug nuts on older cars he recommends seating nuts by hand before tightening them. "Tire stores have gotten really bad about this," he cautions. "A kid with an impact can jam the lug nut on before the lug seats have a chance to line up." The consequences should be obvious.

And some of us are responsible for a potentially ill fit. It's popular to mount Buick drums to old Fords. However, early Ford disc wheels with the 5.5-inch pattern (and some of their reproductions) mount over a larger diameter than the Buick drum offers. Because most of the Buick-style drum covers maintain the same external dimensions they too suffer the same problem as I discovered on my own car. If the wheel doesn't seat properly it possibly won't roll true. There's a fix for that, though.

Alignment

Sometimes an elusive shimmy or vibration stems from an improper wheel alignment. The two main culprits are toe and caster.

Toe

Toe describes the longitudinal relationship between two wheels on an axle. Toe-in: wheels point toward each other in the direction of travel; toe-out: wheels point away from each other in the direction of travel.

The front wheels on most rear-drive road cars benefit from a touch of toe-in. It compensates for the road force that can induce a toe-out condition. Toe-in also eliminates lash in the various components, which enhances straight-line stability.

Excessive toe-in can induce a bear of a shake. It causes the tires to fight each other for traction and the rapid release/traction cycle can cause a shake. It also wears tires unevenly, which causes its own problems.

Toe settings vary by suspension design so start with the specs that the original manufacturer determined for the suspension under your car. But don't treat these specs as if they're set in stone. Your vehicle's dimensions may differ considerably from what the manufacturer intended so you may have to slightly alter toe settings. Remember that bias-ply tires neither need nor tolerate as much toe as radial tires do.

Caster

Caster in a roundabout way generates tracking stability. It refers to the Steering Axis Inclination (SAI)—the line plotted through the kingpin or through both ball-joint centerlines—as viewed from the wheel face.

What actually generates the stability is the relationship between the point where the SAI intersects the ground and the tire's contact patch. Most vehicles feature negative caster, meaning the tire follows the point where the SAI intersects the ground. In fact, motorcyclists express this tracking-stability dimension by the distance that the tire "trails" the SAI where it intersects the ground. Increasing this distance increases the force by which the front wheels center themselves. That makes a car feel more stable at speed.

But that force sword has a second edge: excessive caster/trail can generate enough force to steer the wheel beyond center and slightly into the other direction. If conditions are just right the centering forces can volley the wheel rapidly left and right in a shimmy. Motorcyclists have a more descriptive term for this too: Death wobble or tank slapper. Anyone who's experienced it in a car or on a bike can testify that it's terrifyingly scary and it goes away only if you reduce speed dramatically.

Again, refer to the specifications for the suspension under your car and prepare to alter them if the suspension came from another vehicle. Most suspensions benefit from a touch more caster than stock but too much caster can induce a shimmy.


5. It sounds like magic but when a wheel rolls these beads orient themselves inside the tire to counter imbalance. Unseat the bead and drop the beads into a tubeless tire or use supplied bottles to feed them into a tube's valve-stem hole. Innovative Balancing's ceramic Dynabeads may outlast the car they're in.

6. A dial indicator should be part of every enthusiast's toolbox. Run it against the side of the bead to measure lateral runout and against the inside diameter of the bead to measure radial runout.

7. Because it's so close to the centerline a hub or axle flange bent even a tiny bit will make a wheel wobble like mad. For this reason most vocational manuals recommend 0.005-inch maximum runout.

8. Early Ford 5½-inch-pattern disc wheels mount over an 8-inch diameter. The Buick drums and their reproduction counterparts offer only 7 inches of mounting diameter. Unable to mount properly, the wheel can wobble. The correction is simple: the plates that Buffalo Enterprises makes extend the surface-mounting pad to 8 inches. At 3⁄16-inch thick they won't deflect where unsupported by a small hub, drum, or rotor cover. Fingers point to where the edge of the mounting pads on Ford wheels dug in without them.