Buying car parts in Illinois

The vibration that will not balance out

This is the most common complaint on a car driven in Chicago and the most commonly misdiagnosed.

A wheel that has struck a pothole hard enough to matter is usually bent at the inner rim flange, where it is invisible with the tyre fitted and invisible from outside the wheel arch. It holds air perfectly. It is out of round, or laterally out of true, or both.

Balancing corrects mass distribution. It cannot correct shape. So the wheel comes back balanced and the vibration is still there, the tyre gets blamed, a new tyre goes on, and the vibration is still there.

The measurement that settles it is runout, taken with a dial indicator against the rim flange with the tyre still on — radial for out-of-round, lateral for wobble. Both have limits, and a wheel outside them cannot be balanced into acceptability.

What else the same impact reached

The rim is the visible casualty. The energy went further.

1. 1The wheel bearing. A sharp impact brinells the races — small indentations at the points the balls were loaded against. The bearing is silent that week and rumbles three months later, which is why the pothole is never blamed.
2. 2The steering geometry. Camber and toe move when a control arm or a strut takes a hit. The symptom is a pull, or a wheel that tramlines, or tyres that start wearing on one shoulder.
3. 3Control arm bushings. Rubber tears under shock loading, and the result is a clunk over expansion joints with vague steering either side of centre.
4. 4The strut itself. A bent rod binds. It shows up as a knock on rebound and a car that never quite settles after a crest.
5. 5The tyre's internal structure. A sidewall bulge is a broken cord and it is not repairable — it is a tyre to replace immediately rather than watch.

An alignment after a significant impact is not an upsell. The geometry moved when the component did, and driving on it destroys a set of tyres.

Straight, fast, and full of freight

Outside the city, Illinois is flat and it is one of the most important freight corridors in the country. Interstate driving here is sustained, high-speed and often behind or beside heavy trucks.

That is a completely different wear profile from the city car described above. Brakes last a very long time — sometimes long enough to corrode before they wear out, which is its own problem and the reason a rotor can need replacing at half its remaining thickness. What accumulates instead is hours at load on everything that rotates.

Crosswind matters more than people expect on open prairie. A car that is constantly being corrected against a side wind loads the steering, the tyres and the suspension bushings asymmetrically, and it is one of the reasons a highway car here can need an alignment without ever hitting anything.

Two vehicles, one state

Illinois produces two used cars that look identical on the odometer and are nothing alike.

A Chicago car with 60,000 miles has worn suspension, worn brakes, at least one wheel that has met a kerb, and an engine that has rarely reached full operating temperature. A downstate car with 60,000 miles has excellent brakes, tired bearings, high-hour tyres and a drivetrain that has spent its life at a steady 70 miles per hour.

Inspect accordingly. On the city car, suspension and wheels first. On the highway car, listen for a hum that rises with road speed and ignores engine speed, which is a bearing, and a click on full lock at low speed, which is a constant-velocity joint.

Emissions testing, in the north-east and Metro East

Vehicle emissions testing applies in the Chicago metropolitan area and parts of the Metro East region rather than statewide, and the requirement depends on vehicle age and registration location. Confirm the current rules with the state programme before a test is due.

On anything from 1996 onward the test reads the OBD-II system. A lit check engine light fails it outright, and so does a set of readiness monitors that has not completed after a code clear.