by Jim Kerr
Keeping your vehicle travelling in a straight line on slippery and rutted winter streets can be a challenge. Rough roads and cold, stiff suspensions tend to bounce a vehicle around. Dragging brake pads and shoes can cause a vehicle to pull and make it difficult to keep straight, but so can other vehicle problems. Incorrect wheel alignment is one of them.
In an ideal world, your vehicle’s wheels and tires would sit perfectly vertical and point straight ahead. Tires would have their maximum contact with the road and there would be no bumps on the road. Sounds great, but a vehicle’s suspension has many moveable parts and wherever there is a joint, there is a little play or movement. Correct wheel alignment tends to compensate for this play and more.
There are three main angles measured when an alignment is performed on a vehicle: Camber, caster and toe. Camber is the in or out tilt of the tire at the top. Most vehicles will have close to zero degrees camber, which means the tire is sitting vertically. Performance vehicles may have the tire tipped in at the top so during cornering the body roll will bring the camber close to zero for the best traction. As long as the camber is within about ½ degree from side to side, it will not cause a pull but if the camber is higher on one side, the vehicle will pull to that side. A vehicle pull on icy roads can handling problems.
Caster is the angle of the pivot or steering point for the wheel. Think of the wheels on a shopping cart. The castor wheels provide easy turning and directional stability. Increased castor provides better directional stability but makes it more difficult to turn corners, so caster is always a compromise set to balance the vehicle’s stability and steering. A vehicle will pull to the side with the least castor but slight variances from side to side won’t affect handling much.
Toe is the most critical angle for stability on slippery roads. The tires must point straight ahead when driving down the road. If the wheels are pointed too far toe-out (further apart at the front than at the rear of the tire), the car will try to steer with one front tire and then the other. On good road surfaces, the vehicle may wander slightly but the most noticeable problem is fast tire wear. On icy roads, the vehicle can behave like it has a mind of its own and may even try to spin every time the brakes are applied.
Rear wheel toe angles are just as important as front wheel toe settings. If the rear wheels are set with toe out, the vehicle has a tendency to swap ends during braking because the weight transfer to the front of the vehicle reduces rear wheel traction. Then the rear end will dart in the direction of the wheel with the most toe-out.
Wheel alignment can go out of specification because of wear on suspension components, hitting curbs hard so that alignment adjusters are moved out of position, accidents that can bend suspension parts, or springs that have fatigued and changed the normal riding height of the vehicle. Many drivers think of having the alignment checked on their vehicle after spring potholes have been patched. This may be a good time, but it is just as important to have correct alignment for winter driving.
When a technician does a wheel alignment, the suspension will be checked for damage or wear, tire pressures will be adjusted and the steering angles will be checked. Four wheel alignment is best for any vehicle because it allows technicians to check rear wheel angles even on vehicles with solid rear axles. Camber and caster angles are not adjustable on a few vehicles, but the toe angle will be adjustable. If the camber or caster is out of specification, then parts may need replacing or special adjustment kits from aftermarket suppliers may be available to that will enable the angles to be set.
Wheel alignments are usually done because the driver wants to prevent tire wear. Keeping your vehicle stable on slippery roads is another good reason to make wheel alignments part of your regular vehicle maintenance.