Alignment Caster Shim Kit
SPC Performance 84690 Honda Caster Adjustment Spacers 1/16 Inch (10-Pack)
What Are Alignment Caster Shim Kits?
Caster is one of the three fundamental wheel alignment angles — alongside camber and toe — and it plays a defining role in how your vehicle steers and tracks down the road. Caster refers to the forward or backward tilt of the steering axis relative to a true vertical line when viewed from the side of the vehicle. When this angle falls out of spec, drivers often notice pulling to one side, vague or darting steering feel, or instability at highway speeds. An alignment caster shim kit is one of the most straightforward tools available to correct this problem without the cost of major suspension modifications.
How Caster Shim Kits Work
Caster shim kits consist of precisely angled shims that are installed between suspension components — typically between a control arm and the frame bracket, or between a leaf spring perch and the axle — to rotate the axle or control arm rearward or forward by a specific number of degrees. This wedge-shaped correction effectively dials in the caster angle to match factory specifications or to achieve a custom alignment target suited to your driving needs.
Many solid-axle trucks and 4WD vehicles have no built-in caster adjustment from the factory. When a leveling kit or lift kit raises the front end, the factory caster angle is disturbed and must be corrected separately. As a rule, too little positive caster causes unstable, darting steering, while too much makes the steering feel heavy and reluctant to turn. A properly selected caster shim restores that ideal balance of steering returnability, straight-line stability, and comfortable handling.
Shim kits typically come in multiple thickness increments — from as little as 1/32-inch to several degrees of angular correction — and many designs are stackable, allowing installers to combine shims for larger corrections without purchasing a separate kit. Some advanced shim designs can correct both caster and camber simultaneously with a single tapered component, minimizing the complexity of the alignment process.
When Do You Need a Caster Shim Kit?
- After installing a lift or leveling kit on a solid-axle truck or 4WD — one of the most common applications
- Restoring worn or sagged suspension where ride height has dropped below OEM specs, shifting all alignment angles out of range
- Vehicles with fixed caster geometry that have no factory provision for caster adjustment
- Performance tuning where added positive caster is desired for improved high-speed stability or off-road handling
Choosing the Right Caster Shim Kit
The most important factors when selecting a caster shim kit are the degree of correction required, the specific suspension geometry of your vehicle, and the material and fit of the shim itself. Always consult an alignment printout before ordering so you know exactly how many degrees of correction are needed. Shims are available for a wide variety of platforms — from classic muscle cars with double A-arm front suspensions to modern trucks and Jeeps with solid front axles.
Top Brands in Alignment Caster Shim Kits
When it comes to precision alignment hardware, SPC Performance stands apart as the dominant force in this category. Founded in 1971 and headquartered in Longmont, Colorado, SPC Performance (Specialty Products Company) has been an industry leader in automotive alignment solutions for decades — trusted by professional mechanics, off-road builders, and performance enthusiasts alike. Their caster shim kits are designed and tested in the USA, covering an exceptionally wide range of applications from early Jeeps to modern solid-axle trucks, and many feature a stackable design that gives installers maximum flexibility in dialing in the exact correction needed.