Hi guys. There's a couple of things to be aware of. First of all, a few car models use different width wheels and tires on front and back. No model was listed, but that would mainly apply to a Firebird. Second, GM likes to complicate their rear disc brakes by building the parking brake mechanism into the calipers. Those can require additional clearance and a front wheel could rub if used on the rear.
As a side note, some cars use left and right wheels that are different. The spokes are shaped to direct air flow for brake cooling. That is different than the need to install directional tires to roll the right way.
Another issue has to do with "scrub radius". Without going into a lot of detail, that non-adjustable alignment angle has a huge effect on handling, braking, and directional stability. Anything that changes scrub radius reduces those driving characteristics, often to the point a lawyer or insurance investigator uses it to shift the blame for a crash from their client who ran the red light, onto you. They will convince a jury you were partly at fault because you were less able to avoid the crash, and they may be right.
Scrub radius is shown by drawing an imaginary line between a front wheel's steering pivot points until that line bisects the tire's tread at the road surface. Those pivot points are the lower ball joint, and could be the upper ball joint or the upper strut mount. Things that change scrub radius from what was carefully designed in include tires with a different outer circumference, wheels with a different offset, and possibly wider wheels.
In some cases the manufacturer needs to use a specific wheel and tire on the front to achieve the scrub radius that car needs, but they want to have a wider stance in the rear to give a sporty or high performance look. Those front and rear wheels could interchange, but it's the scrub radius that will be affected.
Another issue that is typically overlooked is the wheel's offset is designed to place the car's weight directly over the rear axle bearing. In the front, it places the weight over the larger inner wheel bearing. This applies to the tapered bearings that all rear-wheel-drive cars used as far back as the '40s and '50s. The job of the smaller outer wheel bearing is only to hold the wheel straight up and down. It is not strong enough to support the car's weight.
Sometimes a manufacturer will develop a new suspension system design for the next model year, but to save money, they'll use perhaps a rear axle design from the previous year. The two designs might only work together to provide proper handling or steering response if those systems are modified a little, and the easiest way to do that might be with wheels that are wider or have a different offset.
You may be able to get a clue as to the difference by looking at the spare tire. That must be able to be used on the front or the rear.
Monday, April 17th, 2017 AT 9:48 PM
