Front-to-Rear Circumference Calculator

This calculator works by computing the circumference of each axle's tire and reporting the gap in millimeters and percent. The gap is the difference in distance each axle covers per wheel turn.

1. Enter the front size, for example 265/35R21 (2,258 mm).
2. Enter the rear size, for example 295/30R21 (2,232 mm).
3. Read the gap: −27 mm per turn.
4. Read the percentage: −1.18%.

The formula is Gap (%) = (Rear Circumference − Front Circumference) ÷ Front Circumference × 100.

Worked example: 225/45R18 front is 2,073 mm and 245/40R18 rear is 2,052 mm. The gap is −20 mm, or −0.99%.

The conversion table compares the circumference of 8 front and rear pairs. Gaps run from −2 mm (−0.07%) to −27 mm (−1.18%).

The 245/45R19 with 275/40R19 pair is the tightest at −0.07%. Pairs above 1% need a check against the vehicle maker's limit.

The Front-to-Rear Circumference Calculator is a tool that compares rolling distance between the front and rear axles. It matters on vehicles with different sizes front and rear, and on all-wheel-drive and 4WD vehicles.

On AWD vehicles, a circumference gap makes one axle try to turn faster than the other. The center coupling absorbs that difference as slip and heat.

This calculator has 4 uses: AWD staggered checks, coupling protection, sensor checks and replacement planning.

• Check AWD staggered setups: Confirm the gap is inside the maker's limit.
• Protect couplings: Reduce slip in center differentials.
• Check sensors: Avoid false wheel-slip signals.
• Plan replacements: Replace one axle's tires without a large gap.