HOW TO TELL IF YOUR WHEELS OR TIRES ARE BENT.

The most annoying things that can happen to any car is when it picks up some kind of vibration. A shaking car can be no fun at all to drive.

Do you feel the vibration at a certain rate of speed?

 A vibration that has a “sweet spot” at a certain speed range is a classic symptom of harmonic modulation caused by a small bend. A wheel and tire assembly that is out of round will have a specific harmonic frequency as it spins, depending on how many bends, the severity of the bends, tire wear and other factors. As the speed changes, the harmonic changes, or modulates, as well. At certain speed ranges this modulation can reach a frequency that will overwhelm the vibration-dampening capacities of the suspension. That's the point at which you begin to feel a vibration in the car that was previously being damped out.

Vibration in the brake pedal under hard braking?

If under moderate to stiff braking pressure you can feel the brake pedal shake under your foot, this is a good indication that what you have is a warped brake rotor or other brake-related issues. The brake rotor must be either replaced or re-lathed to make it perfectly flat.

Once we understand the history of the vibration, the next step is to inspect the wheels and tires. 

The best way to do this is to remove all four wheels and spin the wheel and tire assembly on a balance. Once the wheel is on the balance, it should be spun by hand. With the wheel centered and spinning, we look carefully at the outer edges of the wheel on both the inboard and outboard faces. 

Factory tolerances for a wheel are about .030” (30 thousandths of an inch) both lateral (side to side) and radial (up and down). Most deflections or bends outside that range will be visible to the naked eye while the wheel is spinning centered. 

If the wheel is straight, the line formed by the outer edges of the rim should be relatively stable, and it should not wobble from side to side.

If the wheel is straight, determine if the tire is out of round. Put your eyes level with the tread surface as it spins and look straight across the surface. Does the tread bounce up and down without an equivalent motion in the wheel? The tire is probably out of round. A steel belt may be bent or delaminated inside the tire, or the tire may be wearing irregularly. Look at the tire straight on; do the tread blocks wiggle from side to side? This indicates that the tires are getting lateral wear, usually as a result of an alignment issue.