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Alignment
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While having this service performed on your vehicle is often simply referred to as an "alignment" or "wheel alignment", it is actually a complex operation where your cars suspension angles are measured, and a variety of suspension components are being adjusted. Think of getting an alignment like a suspension system "tune-up". Alignments influence not only the operation of a vehicle's tires, but also the way the vehicle handles and steers.
"Out-of-alignment", occurs when the suspension and the steering system are not working at their desired angles. In older vehicles, these conditions are most often caused by spring sag or suspension wear (bushings, ball joints, etc.) Another way to put the suspension out of alignment is an impact with a pothole or curb. Incorrect alignment usually results in more rapid tire wear.
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The alignment of your vehicle should be a) checked whenever new tires or suspension components are installed, and b) whenever unusual tire wear patterns appear. You should also consider having your alignment checked after your vehicle has encountered a major road hazard or curb.
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There are three different types of alignment that we at Heather Cannon Honda offer and they are front-end, thrust angle, and four wheel.
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A front-end alignment only adjusts and measures the front axle angles. Front-end alignments are okay for some vehicles with a solid rear axle, but checking to make sure that the front tires are positioned to track directly in front of the rear tires is also important. Most cars need more than just a front end alignment.
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The thrust angle alignment is used to make sure the front and rear wheels are tracking correctly on a solid rear axel vehicle. Our technicians here at Heather Cannon Honda would perform the alignment to confirm that all four tires are "square" with each other. This type of alignment also identifies vehicles that would "dog track" while going down a road with the rear end offset from the front.
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The four-wheel alignment is appropriate for vehicles with four-wheel independent suspension, or front-wheel drive vehicles with adjustable rear suspension. This type of alignment "squares" the vehicle in the same way that a thrust angle alignment does. There is more work involved, as this procedure includes adjusting and measuring the rear axel angles as well as the front. This is the most common sort of alignment performed today.
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There are four primary static suspension angles that should be measured and adjusted and those are the caster, camber, toe, and thrust angle. Here are the definitions of each of these angles and the influence they have on the vehicle.
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The angle that we call "Caster" is used to tell the forward or backward slope of a line drawn through the upper and lower steering pivot points, when viewed directly from the side of the vehicle. Caster is expressed in degrees and is measured by comparing a line running through the steering system's upper and lower pivot points of your steering system, to a line drawn perpendicular (straight up and down) to the ground. Caster called "positive" if the line through the steering points slopes towards the rear of the vehicle at the top, and "negative" if the line slopes towards the front of the vehicle.
Why isn't caster the same on all vehicles? Caster angle settings allow the vehicle manufacturer to come up with the correct balance of steering effort, high speed stability and front end cornering effectiveness that they want to achieve. Increasing the amount of positive caster increases steering effort and makes for better straight line tracking, and improves the vehicles high speed stability and provides more effective cornering. Positive caster also makes the tire lean more, when cornering, as the steering angle increases.
When a vehicle doesn't have power steering, it makes it harder to steer when the positive caster is increased. Besides that though, positive caster provides steering improvements by increasing the lean of the tire when the vehicle is cornering while returning it to a more upright position when driving straight ahead.
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The angle that is called "Camber" tells how far the tires slant away from vertical when viewed directly from the front or back of the vehicle. Camber is measured in degrees of tilt from the vertical. Camber is called "negative" when the top of the tire tilts in towards the center of the vehicle and "positive" when the top of the tire leans away from the center of the vehicle.
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The suspension angle called "Toe" measures the exact direction the tires are pointed compared to the centerline of the vehicle when viewed from directly above. Toe is expressed in either degrees or fractions-of-an-inch, and an axle has "positive toe" or "toe-in" when if you run an imaginary line through the centerlines of the tires, the lines intersect in front of the vehicle, and have "negative toe" or "toe-out" when they spread apart. Toe settings are generally used to help compensate for the suspension "give" built in for ride comfort, in order to help tires wear longer. Toe can also be used to adjust the vehicle's handling.
A front-wheel drive vehicle "pulls" the vehicle along through the front axle, resulting in forward movement of the suspension arms against their bushings. So most front-wheel drive vehicles use some negative toe-out to compensate for the movement, so that the tires can run parallel to each other at speed. But a rear-wheel drive vehicle "pushes" the car and the front axle's tires as they roll along the road. Because the tires make some resistance when they roll, this causes a little "pull" or "drag" toward the back of the car, which results in a rearward movement of the suspension arms against their bushings. So most rear-wheel drive vehicles use some positive toe-in to compensate for the movement, so the tires to run parallel to each other at speed.
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The vehicle's toe is one of the most important settings in an alignment as it relates to tire wear. A toe setting that is just a little off its correct setting can mean a big difference in how your tires wear. If the toe setting is just misadjusted by 1/16-inch off, each tire on that axle will scrub almost seven feet sideways every mile! As an example, that translates to the front tires "scrubbing" in a sideways motion over 1/4-mile during every 100 miles you drive! Incorrect toe robs you of tire life, and negatively impacts handling.
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The thrust angle is an imaginary line drawn perpendicular to the rear axle's centerline. It compares whether the rear axle is lined up with the centerline of the vehicle. It also tells if the rear axle is parallel to the front axle and also that the wheelbase on both sides of the vehicle is the same.
If the thrust angle is not correct on a vehicle with a solid rear axle, sometimes more than an alignment is needed, it might need a trip to the body shop to straighten the frame and position the rear axle correctly.
If a vehicle has independent rear axles, (also called independent rear suspension) it can have incorrect toe-in or toe-out on both sides of the axle, or may have toe-in on one side and toe-out on the other. This can be adjusted in an alignment.
The suspension on each side of the vehicle is adjusted individually until it is at the correct toe setting for its side of the vehicle. Incorrect thrust angles can be caused by either an out-of-position axle, or incorrect toe settings. So in addition to the handling problems brought about by incorrect toe, incorrect thrust angles could cause the vehicle to handle differently when turning one direction vs. the other.
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The vehicle manufacturers' alignment specifications generally provide for a "preferred" angle for camber, caster and toe. The correct thrust angle is always zero. The manufacturers also provide the acceptable "minimum" and "maximum" angles for each of the specifications. The minimum and maximum camber and caster specifications typically result in a range that remains within plus or minus 1-degree of the preferred angle. If an alignment can't get the vehicle to the recommended settings, sometimes replacing worn suspension parts is the way to get the vehicle in alignment.
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Getting an accurate wheel alignment is the most important step to balance the wear and performance your vehicle's tires deliver. And getting wheel alignments on a regular basis will usually save you as much in tire wear as they cost, and should be considered part of your vehicles routine, preventative maintenance. It really is like getting your suspension system "tuned up".
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