Why tyre size affects speedometer reading Changing tyre size can alter the overall rolling diameter of the wheel and tyre combination.
If the new tyre has a larger diameter, the vehicle may travel slightly further per wheel rotation. If it has a smaller diameter, it may travel slightly less far per wheel rotation.
What this means in practice A larger rolling diameter can make the actual road speed slightly higher than before at the same indicated speed. A smaller rolling diameter can make the actual road speed slightly lower than before.
What to check before changing tyre size Rolling diameter difference Wheel and tyre clearance Load index and speed rating Vehicle handbook and tyre placard data Insurance and local legal requirements Back to Tyre Size Guides
Disclaimer This tool is provided for general informational purposes only and does not constitute professional, technical, or legal advice.
While we make reasonable efforts to ensure the information and calculations are accurate, we make no representations or warranties, express or implied, regarding completeness, accuracy, reliability, or suitability for any particular purpose.
Use at Your Own Risk Use of this tool is entirely at your own risk. You are solely responsible for verifying all outputs before relying on them.
No Liability (to the extent permitted by law) To the fullest extent permitted by applicable law, we disclaim all liability for any loss or damage, including but not limited to direct, indirect, incidental, or consequential loss arising from use of this tool.
User Responsibility Tyre and wheel changes can affect vehicle safety, handling, braking performance, clearance, speedometer accuracy, legal compliance, and insurance validity. You must independently verify all tyre sizes, wheel fitments, load indices, speed ratings, and manufacturer approvals with a qualified professional, tyre retailer, or vehicle manufacturer before making any decisions.
Always check vehicle handbook data, placard information, and local laws before making any tyre or wheel changes.