Front-to-Rear Circumference Calculator
Calculate the circumference difference between front and rear axles. Check AWD and 4WD tire matching in mm, inches and percent.
Calculate axle-to-axle circumference differences.
Front-to-Rear Circumference Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Front-to-Rear Circumference Calculator Works?
The Front-to-Rear Circumference Calculator works by finding the rolling circumference of the front and rear tires and subtracting one from the other. The tool uses 3 steps.
Enter both axles
Type the front and rear sizes, or measured circumferences when tires are worn.
Compute circumferences
The calculator multiplies each diameter by π.
Report the gap
The calculator returns the gap in mm, inches and percent, and the extra rotations per kilometer on the shorter axle.
Front-to-Rear Circumference Calculator Formula
The Front-to-Rear Circumference Calculator formula is ΔC = C_rear − C_front = π × (OD_rear − OD_front).
ΔC = π × (OD_r − OD_f)ΔC% = ΔC ÷ C_f × 100ΔR = 1,000,000 ÷ C_f − 1,000,000 ÷ C_r- C_f, C_r
- Front and rear circumference (mm)
- ΔR
- Rotation difference per kilometer
Worked example
A 235/40 R18 front tire rolls 2,027 mm, and a 265/35 R18 rear tire rolls 2,019 mm. The gap is -8 mm (-0.31 in), or -0.39%.
Front-to-Rear Circumference Calculator Conversion Table
The Front-to-Rear Circumference Calculator conversion table shows the axle-to-axle circumference gap for 5 staggered setups.
| Front / rear | Front circumference | Rear circumference | Gap | Gap (%) |
|---|---|---|---|---|
| 235/40 R18 / 265/35 R18 | 2,027 mm | 2,019 mm | -8 mm (-0.31 in) | -0.39% |
| 245/40 R19 / 275/35 R19 | 2,132 mm | 2,121 mm | -11 mm (-0.43 in) | -0.52% |
| 225/45 R18 / 255/40 R18 | 2,073 mm | 2,077 mm | +5 mm (+0.19 in) | +0.23% |
| 255/40 R20 / 295/35 R20 | 2,237 mm | 2,245 mm | +8 mm (+0.31 in) | +0.35% |
| 235/35 R19 / 265/30 R19 | 2,033 mm | 2,016 mm | -17 mm (-0.68 in) | -0.85% |
What is Front-to-Rear Circumference Calculator?
A Front-to-Rear Circumference Calculator is a tool that measures the rolling circumference gap between a vehicle's front and rear tires. The center coupling of a 4WD or AWD vehicle sees that gap as constant slip.
Many AWD makers state limits as a circumference gap, for example 6 mm (1/4 in), or as a tread depth gap. A new rear pair with worn fronts often breaks the limit.
The calculator accepts measured circumferences, so the result reflects actual tread wear.
What are the uses of Front-to-Rear Circumference Calculator?
There are 4 main uses of the Front-to-Rear Circumference Calculator, including AWD protection and new-pair checks.
AWD protection
Keep the axle gap inside the maker's limit.
New-pair checks
Check new tires on one axle against worn tires on the other.
Part-time 4WD use
Confirm the gap before locking the transfer case on pavement.
Staggered approval
Confirm a staggered set suits an AWD car.
Related Core Tire Dimensions Tools
View All 134 Subtools →Compare two tire sizes.
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Calculate absolute and percentage differences.
Estimate nominal circumference.
Compare estimated rolling distances.