A pull to the left or right, when driving, may have many causes. Improper wheel alignment is one, but not the most common. Before requesting a wheel alignment, we can check several things which may be the cause.
Pulling only on certain roads
Engineers never build roads perfectly level. They intentionally slant the road toward the side with the drainage. Slightly sloping the road allows rain to run off. The slope or road crown also causes a vehicle to pull slightly in the direction of the slant. In the US most road drainage is on the right side. Most roads also slant slightly to the right to allow water to run off.
A skilled wheel alignment technician offsets the vehicle alignment very slightly. This allows for a road crown. With a properly set wheel alignment the vehicle drives straight, on most roads.
When the drainage is on the left, the vehicle may slightly pull in that direction. The same can also happen if the road crown is excessive or flatter than normal. This type pull is slight and not noticeable to most drivers. A road crown is not an alignment problem. No vehicle will drive perfectly straight on all roads. Proper wheel alignment allows for road crowns on most roads.
Checking for tire conicity
Very often a tire can cause our vehicle to pull. This may be from tread wear or can happen with a new tire. Tire conicity is a defect in a tire that causes a hard pull in one direction. Conicity results from poor manufacturing. We notice this in new tires, often after the first rotation.
With conicity, they do not perfectly align the belts, under the tread of the tire. More belting to one side causes the tire to inflate in a cone-shape. Properly aligned belts inflate squarely, across the tread. Because of the cone shape, a tire with conicity will cause a pull. A characteristic of conicity is a pull that gets worse as the vehicle travels faster. As a test for this problem, we temporarily cross the two front tires. If the vehicle now pulls in the other direction, we must resolve this problem, before proceeding.
A tire separation is another problem that may also cause a pull. With a tire separation, air has forced the belts to separate from the tire carcass. This is very dangerous and the tire may unexpectedly fail. Very often a shake or shimmy may also show up, especially at low vehicle speed.
Air pressure, wheel alignment and low tires
Uneven air pressure is a very common reason for a vehicle to pull to one side. When the pressure in a tire is lower on one side, the height of the tire changes. This causes the wheel alignment to change. An under inflated tire also has more rolling resistance, making the pull more noticeable. Always verify the air pressure in all tires when a vehicle starts to pull. Another tip is to check the rear tires. A low rear tire can also change front wheel alignment and cause a pull. This is most prevalent on vehicles with a short wheel base.
Unequal air pressure is a very common reason for a vehicle to pull to one side. Low air pressure in a tire causes the height of the tire to change. The low tire makes the vehicle lean and this causes the wheel alignment to change.
An under inflated tire also has more rolling resistance. Additional resistance makes the pull more noticeable. We should always verify the air pressure in all tires when a vehicle starts to pull. Checking the pressure in the rear tires is equally important. A low rear tire also changes front wheel alignment and may cause a pull. This problem is most prevalent on vehicles with a short wheel base.
New tires go on the rear
The tread pattern and wear on a tire can also cause it to pull. Different brands and even the same brand, with different wear patterns, do not have the same rolling characteristic. For instance, replacing one tire in a set may cause a pull. If we place the new tire on the front, with an older tire, the vehicle may not drive straight. Replacing tires in pairs is always best, and the new tires should go on the rear.
Investigate any pull that starts after moving the tires
Often people notice a pull shortly after rotating the tires. This may happen for several reasons. A mismatched tire may have been previously on the rear. When rotated to the front, the problem will be noticeable. If the tire is safe to operate, leaving it on the rear may be the best solution. The slight loss of tread life is less than the cost of immediate tire replacement. Always try crossing tires, before condemning the wheel alignment.
Other causes of a pull when driving
A pull related to the brakes
With a wheel alignment problem, the pull will be consistent. The vehicle will drift in one direction, whenever we release the steering wheel. When we need something else to initiate the pull, odds are it is not a wheel alignment problem. For instance, a pull only when applying the brakes, is a brake problem or a loose suspension component. We know this because the vehicle drives straight when we are not applying the brakes.
A single brake may also stay applied after released. With a sticking caliper, wheel cylinder or even a hydraulic fault one brake may remain applied. A dragging brake may cause the vehicle to drift in the direction of the problem. Such a problem will normally also cause the brake to get very hot. A burning smell, combined with a pull, might suggest a brake related pull.
Worn suspension parts may also shift position when we apply the brakes. For example, worn lower control arm bushings may allow the arm to move when we brake. This changes the position of the wheel and may cause our vehicle to pull. A symptom is a quick pull when we brake, that gets better when we stop braking. We may also see our steering wheel turn sharply, when rolling slowly and applying our brakes.
A pull when we accelerate
If the vehicle veers to one side on acceleration or only when we apply the throttle, the cause is not wheel alignment. They call this a torque steer and it can have several causes. This article covers the causes for a torque steer. We can test for a torque steer by placing the vehicle in neutral and allowing it to coast. If the pull is not present when coasting, it is not an alignment problem.
A pull that changes direction
When the vehicle pulls to the right at times and to the left at other times, wheel alignment will not be the cause. Alignment can only be off in one direction or the other. Things that bind, in the steering or suspension, often cause a memory steer. We call this ‘memory steer’ because it remembers and pulls in the direction last steered. For example the vehicle may pull to the left after a hard turn to the left or right, after a hard right turn. This can be difficult to diagnose, but often results from binding ball joints, strut bearings or tie rods.
Checking these simple steps, before buying a wheel alignment, can save a good deal of frustration. Better shops automatically check these items. A proper wheel alignment lasts for years, drives straight and prevents tire wear.