Tyre Size Comparison
Compare an existing tyre with a proposed size and see how the nominal sidewall height, overall diameter and circumference change. The speedometer result is a mathematical estimate, not a fitment approval.
Compare two tyre sizes
| Measurement | Current | Proposed | Difference |
|---|
How tyre size comparison works
A tyre size such as 205/55R16 contains three useful inputs for nominal dimensional comparison: section width, aspect ratio and wheel diameter. The nominal sidewall height is width multiplied by aspect ratio divided by 100.
Sidewall height = tyre width × aspect ratio ÷ 100.
Overall diameter = wheel diameter × 25.4 + 2 × sidewall height.
Circumference = π × overall diameter.
Ground-clearance effect
If the proposed tyre has a larger overall diameter and the vehicle geometry remains otherwise unchanged, the nominal axle-center-to-road dimension changes by approximately half of the diameter difference. This is a geometric estimate only.
Speedometer effect
For the same indicated speed, a larger rolling circumference means the vehicle travels farther per wheel revolution. The simple mathematical relationship is:
Actual speed ≈ indicated speed × proposed diameter ÷ current diameter.
Actual vehicle speedometer and wheel-speed systems can have tolerances and may respond to other factors, so this result should be used as a dimensional comparison.
What this tool does not tell you
A numerical comparison does not establish suspension clearance, steering clearance, fender clearance, wheel offset compatibility, load capacity or manufacturer approval. Check those separately for the exact vehicle.
Why nominal sizes are only part of the picture
Real tyre dimensions can vary by manufacturer and construction. Tyre fitment decisions should therefore use the exact product specifications and vehicle requirements rather than relying on nominal calculations alone.
FAQs
Does a larger tyre always improve ground clearance?
Geometrically, a larger overall diameter raises the axle center relative to the road when other geometry is unchanged. That does not guarantee increased clearance at every low point underneath the vehicle.
Can I use this to approve a tyre upgrade?
No. It compares dimensions. Vehicle-specific fitment, load and speed requirements still need verification.
Why can two tyres with the same nominal size differ?
Actual manufactured dimensions can vary with brand, construction and operating conditions.