Wheel and Tire Packages for Lifted Trucks - Square Body

Overview

Selecting the proper wheel and tire package for a lifted 1973-1987 GM Square Body truck is critical for both performance and safety. A lifted Square Body requires careful consideration of wheel offset, backspacing, tire diameter, and load capacity to maintain proper geometry, avoid clearance issues, and ensure reliable operation.

This guide covers wheel and tire selection for Square Body trucks with lift heights ranging from 2" to 8", including both suspension and body lifts. Proper wheel and tire selection affects steering response, ride quality, brake cooling, speedometer accuracy, and overall vehicle dynamics.

Key considerations include:
- Maintaining proper scrub radius and steering geometry
- Ensuring adequate clearance for suspension travel
- Matching load ratings to vehicle weight and intended use
- Preserving brake cooling and ABS function (1987 K-series)
- Correcting speedometer and gear ratio calculations

Common Issues

Clearance Problems

Inner fender interference - Occurs with insufficient backspacing or oversized tires
Control arm contact - Common with wide wheels and aggressive offsets
Brake caliper clearance - Particularly problematic with aftermarket brake upgrades
Steering box interference - Issues with extreme negative offset wheels

Handling and Safety Issues

Increased scrub radius - Causes heavy steering and reduced returnability
Bearing and hub stress - From excessive wheel offset and unsprung weight
Speedometer inaccuracy - Requires recalibration or gear changes
Reduced payload capacity - From lighter-rated aftermarket wheels

Aesthetic Concerns

Wheel well gaps - Disproportionate appearance with incorrect tire sizing
Stance issues - Improper offset creating "sunken" or overly aggressive appearance

Parts & Materials Needed

Essential Components

Wheels:

Recommended Specifications:
- Diameter: 15" to 20" (15"-17" preferred for performance)
- Width: 8" to 12" depending on tire selection
- Backspacing: 3.5" to 5.5" (varies by lift height and width)
- Load Rating: Minimum 2,500 lbs per wheel for C10/K10
- Bolt Pattern: 5x5" (5x127mm) for all Square Body trucks

Popular Wheel Options:
- American Racing AR172 Baja - AR1727973 (17x9, 4.5" BS)
- Method Race Wheels 301 - MR30179550 (17x9, 5.5" BS)
- Pro Comp 69 Series - 5069-7973 (17x9, 4.25" BS)
- Black Rhino Armory - 1790ARY-25127M87 (17x9, 4.53" BS)

Tires:

Common Size Combinations:
Lift Height | Recommended Tire Size | Overall Diameter
2-3"        | 33x12.50R15          | 33.0"
3-4"        | 35x12.50R17          | 35.0"
4-6"        | 37x12.50R17          | 37.0"
6-8"        | 38x13.50R20          | 38.0"

Hardware and Accessories:
- Lug nuts: Dorman 711-321 (Chrome acorn, 1/2"-20)
- Hub-centric rings: Varies by wheel manufacturer
- Valve stems: Standard rubber or TPMS-compatible for 1987 models
- Wheel spacers: Spidertrax 5x5-1.25 if additional clearance needed

Tools Required

Torque wrench - 1/2" drive, 80-140 ft-lb range
Floor jack and jack stands - Minimum 3-ton capacity
Lug wrench - 1/2" or 19mm depending on lug nuts
Measuring tools - Tape measure, calipers for backspacing verification

Step-by-Step Guide

Phase 1: Measurement and Planning

Determine Current Specifications
- Measure existing wheel backspacing with wheel mounted
- Record current tire size and overall diameter
- Document any current clearance issues
Calculate Required Backspacing
```
Formula: Required BS = (Rim Width ÷ 2) + Desired Offset + Hub Face to Inner Fender

Example for 3" lifted K10 with 9" wide wheel:
- Hub face to inner fender: ~5.5"
- Desired offset from hub face: -0.5" (outward)
- Required backspacing: (9 ÷ 2) + (-0.5) + 5.5 = 9.5"
```

Select Tire Size Based on Lift Height
- 2-3" lift: 33x10.50 to 33x12.50
- 4-5" lift: 35x11.50 to 35x12.50
- 6"+ lift: 37x12.50 to 40x13.50

Phase 2: Wheel Selection

Verify Load Rating
- C10/K10: Minimum 2,500 lbs per wheel
- C20/K20: Minimum 3,000 lbs per wheel
- Suburban: Minimum 2,750 lbs per wheel
Confirm Bolt Pattern and Hub Bore
- All Square Body: 5x5" (127mm) bolt pattern
- Hub bore: 78.3mm (aftermarket wheels often 78.1mm)
- Use hub-centric rings if wheel bore is larger
Calculate Final Backspacing
Common Backspacing by Application: - Stock height: 4.5" to 5.0" - 2-4" lift: 4.0" to 4.5" - 4-6" lift: 3.5" to 4.25" - 6"+ lift: 3.0" to 4.0"

Phase 3: Installation

Pre-Installation Check
- Verify wheel specifications match order
- Check tire mounting direction (if directional)
- Inspect hub surfaces for damage or corrosion
Mounting Procedure
Torque Specifications: - Initial: 15-20 ft-lbs in star pattern - Secondary: 50-60 ft-lbs in star pattern - Final: 85-95 ft-lbs in star pattern - Re-torque after 50 miles
Post-Installation Verification
- Check clearance at full lock (both directions)
- Verify suspension travel clearance
- Test drive at low speed for vibration or binding

Phase 4: Calibration and Adjustment

Speedometer Correction
- Calculate percentage change in tire diameter
- Install speedometer gear or electronic correction module
- Common gear changes for 700R4/4L60:
- 33" tires: 19-tooth gear (pink)
- 35" tires: 17-tooth gear (black)
- 37" tires: 15-tooth gear (yellow)
Differential Gear Consideration
- Calculate effective gear ratio change
- Consider regearing for tires over 35"
- Recommended ratios:
- 33" tires: 3.73 to 4.10
- 35" tires: 4.10 to 4.56
- 37"+ tires: 4.56 to 4.88

Year/Model Differences

1973-1980 Models

Wheel bolt pattern: 5x5" across all models
Hub bore: 78.3mm standard
Load requirements:
C10: 2,500 lbs per wheel minimum
C20: 3,000 lbs per wheel minimum
K10/K20: Add 10% for 4WD components
Brake clearance: Generally more forgiving with smaller brake components
No ABS considerations

1981-1987 Models

Consistent 5x5" bolt pattern maintained
Improved brake systems require more clearance consideration
1987 K-series ABS: Requires careful wheel selection to maintain sensor clearance
Fuel injection (1987 TBI): More sensitive to speedometer accuracy for proper operation

Model-Specific Considerations

C10/C20 (2WD Models):
- Lower ride height allows smaller lift/tire combinations
- Less stress on drivetrain components
- Simpler suspension geometry
- Better fuel economy with moderate tire sizes

K10/K20 (4WD Models):
- Higher stock ride height accommodates larger tires
- Front differential adds clearance constraints
- CV joint angles affected by extreme lifts
- Transfer case considerations with tire diameter changes

K5 Blazer:
- Shorter wheelbase affects tire size proportions
- Spare tire mounting limitations with larger tires
- Weight distribution considerations
- Tailgate clearance with oversized spare

Suburban:
- Heaviest model requires highest load-rated wheels
- Longest wheelbase handles large tires well
- Rear overhang considerations with approach angles
- Family hauling requirements favor moderate sizing

Tips & Best Practices

Selection Guidelines

Wheel Sizing:
- Stay conservative with diameter - 17" maximum for daily drivers
- Prioritize backspacing over offset - More critical measurement for clearance
- Consider unsprung weight - Lighter wheels improve ride and handling
- Match finish to intended use - Chrome for show, powder coat for durability

Tire Selection:
- Choose load range C or D for durability and load capacity
- Prioritize tread pattern for use - A/T for daily driving, M/T for off-road
- Consider sidewall strength - Important for aired-down off-road use
- Match tire age - Don't mix old and new tires

Performance Optimization

Balancing and Alignment:
- Road force balancing recommended for large tire/wheel combinations
- Alignment critical after lift - Especially caster and toe settings
- Regular rotation schedule - Every 5,000-6,000 miles for even wear
- Pressure monitoring - Large tires more sensitive to pressure changes

Maintenance Considerations:
- Higher replacement costs - Budget for tire and wheel maintenance
- Increased wear on components - Steering, suspension, and drivetrain
- Fuel economy impact - Larger tires reduce efficiency significantly
- Insurance considerations - Some modifications affect coverage

Common Mistakes to Avoid

Ignoring load ratings - Can lead to wheel failure
Excessive negative offset - Stresses bearings and affects handling
Mismatched tire sizes - Even small differences cause drivetrain binding
Inadequate clearance checking - Must verify at full suspension travel
Forgetting speedometer correction - Affects shift points and fuel mapping

Troubleshooting

Clearance Issues

Inner Fender Contact:

Symptoms: Rubbing noise during turns or suspension travel
Solutions:
- Increase wheel backspacing by 0.5-1.0"
- Trim inner fender lip (permanent modification)
- Reduce tire width or diameter
- Install fender flares for additional clearance

Control Arm Interference:

Symptoms: Contact during steering or suspension compression
Solutions:
- Increase backspacing to move wheel inward
- Modify control arm clearance (advanced)
- Select narrower wheel width
- Adjust suspension geometry

Handling Problems

Heavy Steering:

Causes: Excessive scrub radius from wrong offset
Solutions:
- Verify power steering operation
- Check front end alignment
- Consider different wheel offset
- Inspect for binding in steering components

Vibration Issues:

Diagnosis Steps:
1. Check wheel/tire balance
2. Verify hub-centric ring installation
3. Inspect for bent wheels or damaged tires
4. Check lug nut torque
5. Examine driveshaft angles (4WD models)

Speedometer Inaccuracy

Electronic Speedometers (1987+):
- Install electronic correction module
- Available from Dakota Digital, Painless Performance
- Program for exact tire diameter

Mechanical Speedometers (1973-1986):
- Change speedometer drive gear in transmission
- Calculate required gear using tire diameter ratio
- Gears available from LMC Truck, Classic Industries

Load and Durability Issues

Premature Wheel Failure:

Prevention:
- Verify adequate load rating
- Avoid extreme offset specifications  
- Regular inspection for cracks or damage
- Proper torque specifications

Excessive Tire Wear:

Common Causes:
- Incorrect alignment after lift
- Improper tire pressure
- Overloading vehicle
- Aggressive driving with large tires

Solutions:
- Professional alignment with lift specifications
- Regular pressure monitoring
- Rotate tires every 5,000 miles
- Adjust driving habits for tire size

This comprehensive guide provides the technical foundation for selecting and installing appropriate wheel and tire packages on lifted Square Body trucks while maintaining safety, performance, and reliability.