ALIGNMENT BASICS 101
A major cost of operating a fleet of trucks on the road daily is the cost of tires. Along with a good maintenance program that includes wheel balancing and tire rotation it is always a good idea to follow OEM recommendations for a Front End Alignment.
During my years in the shop having to do an alignment was one of my least favorite tasks. Tire wear patterns were a good indicator as to any incorrect adjustments. As I couldn’t see the angles I had to try to visualize them as I worked and trust my adjustments were correct. Let’s take a minute to look at the basic front end alignment angles:
B Minus A – Camber (Inches)
C- Camber (Degrees Positive)
D – Kingpin Inclination (Degrees)
E Minus F – Toe-in (inches)
G – Caster (Degrees Positive)
K Minus L – Kingpin Inclination (Inches)
WHEEL TOE-IN = Camber (A) equals amount in inches or degrees the top of front wheels are tilted outward or inward from vertical position (C). Camber offsets wheel deflection, due to wear of front axle parts, and prevents a reverse or negative camber condition. Reverse or negative camber is an inward inclination of wheels at the top.
WHEEL CAMBER = Camber (A) equals amount in inches or degrees top of front wheels are tilted outward or inward from vertical position (C). Camber offsets wheel deflection, due to wear of front axle parts, and prevents a reverse or negative camber condition. Reverse or negative camber is an inward inclination of wheels at the top. Extreme or unequal camber between wheels causes improper steering resulting in excessive tire wear.
FRONT AXLE CASTER = Front axle caster is described as the kingpin inclination from the vertical plane in fore and aft vehicle direction (G). Incorrect caster may a result of sagging springs, bent axle, twisted axle, or unevenly tightened spring U-bolt nuts. Ensure all U-bolt nuts are tightened equally. Usually if an axle is twisted caster will be unequal for both right and left side.
KINGPIN INCLINATION = Kingpin inclination is designed into axle end and is described as amount that the top of the kingpin is inclined toward center of vehicle. Kingpin(s) are inclined (D) to assist front wheel return to center once a turn has been completed.
FRAME ANGLE = Caster, camber, and toe-in dimensions are for vehicle at design load (with frame level). If a frame is not level on while sitting on alignment equipment, frame angle must be suspected. This is considered important during a caster angle check to obtain an accurate setting.
When performing an alignment it is always a good idea to have current and up to date specifications. Mitchell1 TruckSeries truck repair software provides wheel alignment charts for most vehicles. Having current up to date specifications helps guarantee a correct wheel alignment and helps prevent unnecessary tire wear.
For some great information and a more detailed explanation on tire wear causes and solutions see Jake Schell’s blog post “Maintenance Tips to Reduce Tire Wear” for further information.
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