Tire Diameter Difference Calculator
Find the exact diameter difference between two tires in mm, inches and percent, and see whether the change stays inside the 3% guideline.
Calculate absolute and percentage differences.
Tire Diameter Difference Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Tire Diameter Difference Calculator Works?
The Tire Diameter Difference Calculator works by computing both overall diameters and reporting the gap as an absolute value and as a percentage. The tool follows 3 steps.
Enter both sizes
Type the current size and the new size in metric format.
Compute both diameters
The calculator applies OD = 2 × W × AR ÷ 100 + Rim × 25.4 to each size.
Report the gap
The calculator returns the absolute gap in mm and inches, the percent change, and a pass or fail against the ±3% limit.
Tire Diameter Difference Calculator Formula
The Tire Diameter Difference Calculator formula is Δ% = (OD_new − OD_old) ÷ OD_old × 100, and the absolute gap is ΔOD = OD_new − OD_old.
ΔOD = OD_new − OD_oldΔOD_in = ΔOD ÷ 25.4Δ% = ΔOD ÷ OD_old × 100- OD_old
- Diameter of the current tire (mm)
- OD_new
- Diameter of the new tire (mm)
- Δ%
- Percent change in diameter
Worked example
Going from 265/70 R17 (802.8 mm) to 285/70 R17 (830.8 mm) adds 28.0 mm (1.10 in). The relative change is +3.49%, which exceeds the ±3% guideline.
Tire Diameter Difference Calculator Conversion Table
The Tire Diameter Difference Calculator conversion table shows the absolute and percent diameter gap for 7 typical one-step size changes.
| Size change | Gap (mm) | Gap (in) | Change (%) | Inside ±3%? |
|---|---|---|---|---|
| 205/55 R16 → 215/55 R16 | 11.0 mm | 0.43 in | +1.74% | Yes |
| 225/45 R17 → 235/45 R17 | 9.0 mm | 0.35 in | +1.42% | Yes |
| 265/70 R17 → 285/70 R17 | 28.0 mm | 1.10 in | +3.49% | No |
| 245/40 R18 → 245/45 R18 | 24.5 mm | 0.96 in | +3.75% | No |
| 215/60 R16 → 225/60 R16 | 12.0 mm | 0.47 in | +1.81% | Yes |
| 275/55 R20 → 275/60 R20 | 27.5 mm | 1.08 in | +3.39% | No |
| 195/65 R15 → 205/65 R15 | 13.0 mm | 0.51 in | +2.05% | Yes |
What is Tire Diameter Difference Calculator?
A Tire Diameter Difference Calculator is a tool that measures how much taller or shorter a new tire is than the current tire, in length units and in percent. The percent figure drives the speedometer, odometer and anti-lock braking system (ABS) effects. The length figure drives clearance and ride height.
Tire and vehicle makers use ±3% as the common limit for a replacement tire's diameter. Many all-wheel-drive (AWD) vehicles need a much tighter match, often under 1% between tires on the same car.
The Tire Diameter Difference Calculator gives a quick yes-or-no answer against the ±3% limit before a buyer orders tires.
What are the uses of Tire Diameter Difference Calculator?
There are 5 main uses of the Tire Diameter Difference Calculator, including tolerance checks and ride height estimates.
Tolerance checks
Test a new size against the ±3% replacement guideline.
Width-change effects
See how a 10 mm width increase changes height when the aspect ratio stays the same.
Ride height estimates
Halve the diameter gap to get the axle lift or drop.
Clearance budgeting
Compare the gap in mm with the free space measured in the wheel arch.
AWD matching
Check that a single replacement tire sits within the AWD maker's diameter limit.
Related Core Tire Dimensions Tools
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