By Jim Kerr
Wheel alignments are one of those forgotten vehicle maintenance items. In the past, drivers usually had an alignment done when new tires were installed. This was a good idea, but with tires lasting for years on some vehicles, alignments need to be performed more frequently than just when tires are changed. I often recommend having it done at least once a year, for increased tire life and vehicle safety.
When you take your vehicle in for an alignment, steering linkages and suspension components are inspected for wear or damage. Worn parts won’t keep the tires in alignment, so they need to be repaired before any adjustments are performed. Older vehicles may need several parts and it can be expensive. Unfortunately, the few shops that sell parts that aren’t needed have damaged the image of reputable shops. If you have any doubts about whether your vehicle needs parts, ask the technician to show you the wear. Reputable shops will explain what they are doing, how they test and show you the wear on the parts. Of course, word of mouth is always a good way to find a quality shop.
With the vehicle inspected, the technician will connect the alignment equipment and take the readings. Four-wheel alignments are the most common type performed. Two-wheel alignments (front only) were the norm in the past but front wheel drive vehicles and those with independent rear suspensions should have all four wheels aligned. This is not as critical on rear wheel drive vehicles with a solid rear axle, such as pickups, but a four-wheel alignment can highlight problems such as bent rear axle housings or an axle housing that’s shifted out of position.
The technician takes several readings. Camber is the tilt of the tire in or out at the top. Theoretically, the tire should be exactly vertical to keep the tread on the ground, but suspension movement, cornering forces and body roll all affect the position of the tire, so often the tire is adjusted slightly away from vertical, typically within half a degree of vertical in or out. Front suspensions are often adjustable, but many rear suspensions have no adjustment. Sometimes aftermarket shims can be used to adjust the angle, but if a rear camber angle is too far out of limits, it indicates a damaged or bent part.
Caster is the difference in angle of a line through the suspension turning pivot points and the vertical center of the tire. Think of a caster wheel on a shopping cart. The wheel is offset around the pivot point to provide directional stability. Rear wheels don’t steer, so caster is not measured. Front wheel caster provides ease of steering and directional stability. The caster angles should be close to equal from side to side with slightly less (one quarter to half degree) on the left side. Slightly less caster causes the vehicle to pull to that side to compensate for the crown on the road, so the vehicle will drive straight.
Correct toe is the most important angle for decreasing tire wear and keeping the vehicle stable. The tires should be pointed straight ahead when driving. To accomplish this, the steering is adjusted either slightly in or out, depending on wheel offsets and suspension design. Too much toe-in will wear tires and excessive toe-out causes vehicle stability problems. It will tend to dart from side to side with the slightest turn of the steering wheel. Rear toe out can cause the back of the vehicle to turn towards the tire with the best traction. This is most noticeable on icy roads during braking, where it can cause the vehicle to spin. If your vehicle handles poorly on slippery roads, get a wheel alignment right away.
Other angles checked include king pin inclination, tire setback and vehicle thrust line. These angles can highlight bent suspension parts or hidden frame damage and that is why an alignment check is often a requirement when importing a vehicle from another province. I have seen a vehicle that looked perfect but the alignment showed the left wheelbase was shorter than the right by 50 mm. The body had been repaired but not correctly.
Wheel alignments may seem an unnecessary expense if the vehicle is driving fine, but correct alignment improves tire life, increases fuel economy and improves handling. It can actually save you money in the long run.