Wheel Alignment & Tire Service

Tires are the only part of the vehicle that contacts the road. Proper tire maintenance and precise wheel alignment directly affect safety, handling, tire life, and fuel economy. This guide covers tire construction, sizing, mounting and balancing, rotation patterns, TPMS, and the geometry of wheel alignment with real-world specifications and adjustment procedures.

Tire Fundamentals

Reading a Tire Sidewall

Example: P225/65R17 102H

Code	Meaning
P	Passenger vehicle (LT = Light Truck, ST = Special Trailer)
225	Section width in millimeters (tread to tread)
65	Aspect ratio (sidewall height is 65% of the section width)
R	Radial construction
17	Wheel diameter in inches
102	Load index (1,874 lbs per tire)
H	Speed rating (130 mph maximum sustained speed)

Common Speed Ratings

Rating	Max Speed	Common Use
S	112 mph	Family sedans, SUVs
T	118 mph	Family sedans, minivans
H	130 mph	Sport sedans
V	149 mph	Performance vehicles
W	168 mph	High-performance
Y	186 mph	Exotic/track performance

DOT Date Code

The last four digits of the DOT code on the sidewall indicate the week and year of manufacture:

• Example: DOT ... 2321 = manufactured in the 23rd week of 2021
• Tires older than 6 years should be inspected carefully; 10 years is the absolute maximum service life regardless of tread depth (NHTSA recommendation)

Tread Depth

• New tires: 10/32" to 12/32" typical
• Legal minimum (most states): 2/32"
• Recommended replacement: 4/32" for adequate wet traction (3/32" minimum for winter)
• Measure with a tread depth gauge at multiple points across the tread face and at multiple circumferential positions
• Uneven wear patterns indicate alignment or inflation problems

Tire Mounting and Balancing

Mounting Procedure

1. Deflate the old tire completely. Break the bead on both sides using the tire machine's bead breaker.
2. Lubricate both beads of the new tire with approved tire mounting lubricant (never use silicone spray, petroleum-based products, or dish soap)
3. Ensure the tire rotation direction arrow (if directional) matches the intended wheel position
4. Mount the tire on the wheel using the tire machine, being careful not to pinch the bead or damage the TPMS sensor
5. Inflate to seat the beads. Maximum pressure to seat beads: do not exceed the max pressure on the sidewall (typically 44-51 PSI for passenger, 80 PSI for LT tires). Reduce to the vehicle's specified operating pressure once beads are seated.
6. Check for bead seating by verifying the molded line near the bead sits evenly around the entire circumference of the rim

Balancing

Wheel balance eliminates vibration caused by uneven weight distribution.

Static imbalance: Weight is uneven top-to-bottom. Causes vertical bouncing (hop).
Dynamic imbalance: Weight is uneven side-to-side. Causes side-to-side wobble (shimmy).

Balancing procedure:

1. Mount the wheel on the spin balancer and enter the wheel dimensions (diameter, width, offset/distance)
2. Spin the wheel. The machine displays the amount and location of imbalance.
3. Apply clip-on or adhesive (stick-on) wheel weights at the indicated positions
4. Respin to verify the balance is within 0.25 oz (7g) or less on each plane
5. For alloy wheels, use adhesive weights to prevent damage to the wheel face

Road force balancing: A road force balancer presses a roller against the tire while spinning to simulate road contact. It measures force variation and can identify tire or wheel defects that cause vibration even when weight balance is correct. Useful for persistent vibration complaints.

Tire Rotation Patterns

Regular rotation (every 5,000-7,500 miles or with every oil change) equalizes wear across all tires.

Front-Wheel Drive (FWD)

• Forward cross: Front tires move straight to the rear. Rear tires cross to the front.
• Front left goes to rear left. Front right goes to rear right. Rear left goes to front right. Rear right goes to front left.

Rear-Wheel Drive (RWD) or All-Wheel Drive (AWD)

• Rearward cross: Rear tires move straight to the front. Front tires cross to the rear.
• Rear left goes to front left. Rear right goes to front right. Front left goes to rear right. Front right goes to rear left.

Directional Tires

• Front-to-rear on the same side only (tires stay on their side of the vehicle)
• Left front to left rear, right front to right rear

Staggered Fitment (Different Size Front/Rear)

• Rotation is limited to same-axle swap only (left to right) if the tires are not directional
• If directional and staggered: tires cannot be rotated at all - they must be demounted, flipped on the rim, and remounted (impractical; usually you just replace when worn)

Tire Pressure Monitoring System (TPMS)

Direct TPMS

• Sensor mounted inside each wheel on the valve stem (most common)
• Transmits pressure and temperature data wirelessly to the TPMS module
• Battery life: typically 5-10 years (non-replaceable in most sensors; replace the whole sensor)
• After service (tire rotation, new tires, new sensors), most vehicles require a TPMS relearn procedure:
  • Self-learn (drive method): Drive at 15-60 mph for 10-20 minutes; the system learns the new positions automatically (Toyota, many Asian vehicles)
  • Manual relearn (tool required): Use a TPMS activation tool at each wheel in sequence while the vehicle is in learn mode (GM, Ford, Chrysler)
  • OBD relearn: Program sensor IDs directly through the DLC with a scan tool (some European vehicles)

Indirect TPMS

• Uses the ABS wheel speed sensors to detect pressure differences (an underinflated tire has a smaller rolling circumference and rotates faster)
• No physical pressure sensor in the wheel
• After service, reset through the vehicle's infotainment menu or button press
• Common on some Honda, BMW, and Mazda models

TPMS Sensor Replacement

• Torque the valve stem nut to 35 in-lbs (4 Nm) for rubber snap-in stems, or per manufacturer spec for aluminum stems
• Replace the sealing washer, valve core, and cap with each sensor replacement
• Always use a plastic valve cap - metal caps can corrode and seize onto the stem

Wheel Alignment

The Three Primary Angles

Camber:

• The inward or outward tilt of the wheel when viewed from the front
• Positive camber: top of wheel leans outward
• Negative camber: top of wheel leans inward
• Typical specification: -0.5 to +0.5 degrees for most vehicles
• Affects tire wear on the inner or outer edge
• Excessive negative camber: inner edge wear. Excessive positive camber: outer edge wear.
• Adjusted by: eccentric cam bolts on strut-to-knuckle, upper control arm shims, adjustable upper control arms, or slotted strut mounts

Caster:

• The forward or rearward tilt of the steering axis when viewed from the side
• Positive caster: steering axis tilts rearward at the top (like a motorcycle fork) - provides straight-line stability and steering return-to-center
• Typical specification: +2.0 to +7.0 degrees positive
• Not directly a tire wear angle, but unequal side-to-side caster causes the vehicle to pull toward the side with LESS positive caster
• Adjusted by: moving the upper strut mount, upper control arm shims, or eccentric cam bolts on the lower control arm

Toe:

• The direction the tires point relative to the centerline of the vehicle when viewed from above
• Toe-in (positive toe): fronts of tires point toward each other
• Toe-out (negative toe): fronts of tires point away from each other
• The most critical alignment angle for tire wear. Incorrect toe causes rapid, even feathering across the tread.
• Typical specification: 0.00 to 0.20 degrees total toe (0.00 to 0.10 per side) for most FWD vehicles
• RWD vehicles often run slight toe-in (0.10-0.20 total) for straight-line stability
• Adjusted by: turning the tie rod sleeves or jam nuts on the inner/outer tie rods

Additional Alignment Angles

Steering Axis Inclination (SAI):

• The angle of the steering pivot axis when viewed from the front
• Not adjustable - used as a diagnostic angle
• If SAI is out of spec, a structural component (knuckle, strut tower, subframe) is bent or damaged

Included Angle:

• SAI + Camber (if camber is negative, it subtracts)
• Useful for pinpointing whether a camber problem is in the knuckle (SAI off) or control arm/strut (SAI normal)

Thrust Angle:

• The direction the rear axle points relative to the vehicle centerline
• If the thrust angle is not zero, the vehicle "dog-tracks" (rear end offset from the front)
• On solid axle vehicles: not adjustable (check for bent axle housing or leaf spring issues)
• On independent rear suspension: adjustable via rear toe and camber adjustments

Alignment Procedure

1. Pre-alignment inspection (critical - do this first):

   • Check tire pressures and set to specification (alignment angles change with tire pressure)
   • Check for worn tie rod ends, ball joints, control arm bushings, wheel bearings, and strut mounts
   • Check ride height (sagging springs change all alignment angles)
   • Check for uneven cargo loading (remove heavy items from the trunk)
   • DO NOT align a vehicle with worn suspension components - fix the worn parts first

2. Position the vehicle on the alignment rack:

   • Drive straight onto the rack
   • Jounce the suspension (push down on each corner and release) to settle it
   • Lock the steering wheel straight ahead with a steering wheel holder

3. Mount alignment heads/targets on each wheel

4. Compensate the sensors (roll compensation or jacking compensation per the machine manufacturer)

5. Read current alignment values and compare to manufacturer specifications

6. Adjust rear alignment first (rear camber and toe), then front

   • Adjusting front toe last ensures the steering wheel is centered

7. Adjust front camber and caster (if adjustable on the vehicle)

8. Adjust front toe last - split the total toe evenly between both sides

9. Center the steering wheel - if the steering wheel is off-center after alignment, adjust the individual tie rods (shorten one, lengthen the other by the same amount) to center it without changing total toe

10. Print the alignment report showing before and after values

Common Alignment-Related Wear Patterns

Wear Pattern	Cause	Fix
Inner edge wear	Excessive negative camber	Adjust camber, check for sagging springs
Outer edge wear	Excessive positive camber	Adjust camber, check for lift kit issues
Feathering (diagonal wear across tread blocks)	Incorrect toe	Adjust toe
One-sided pull	Unequal cross-caster, or unequal cross-camber	Equalize side-to-side caster and camber
Cupping/scalloping	Worn shocks/struts, worn ball joints	Replace worn suspension components
Center wear	Over-inflation	Adjust tire pressure to spec
Both-edge wear	Under-inflation	Adjust tire pressure to spec

Key Takeaways

• Always inspect and repair worn suspension components before performing an alignment
• Toe is the most critical angle for tire wear and the most commonly out of adjustment
• Set tire pressures to the vehicle specification (door placard), not the tire sidewall max
• Perform TPMS relearn after any tire rotation or tire replacement
• Rotate tires every 5,000-7,500 miles using the correct pattern for the drivetrain configuration
• Always balance wheels after mounting new tires, and road-force balance for persistent vibration complaints
• Document before and after alignment readings on the printout for the customer and the shop file