What is Tyre Upsizing?
Tyre upsizing is the practice of replacing your vehicle's factory/stock tyres with wider tyres or larger alloy wheels. Done correctly, it can drastically improve your car's aesthetic, grip, and cornering stability. Done incorrectly, it can ruin your suspension, cause your tyres to rub against the wheel arches, and make your speedometer dangerously inaccurate.
Our Tyre Upsize Calculator takes the guesswork out of "Plus Sizing". It compares the overall diameter of your new setup against your old one to ensure you stay within the industry-standard safety limits.
The 3% Safety Rule
Automotive experts universally recommend that any tyre upsize should not change the total diameter of the wheel/tyre combo by more than ±3%.
- Too Large (> +3%): The tyre may rub against the suspension components or fenders when turning. It also severely impacts braking distance, fuel efficiency, and transmission gearing.
- Too Small (< -3%): You will lose significant ground clearance, making the car prone to scraping on speed breakers. The ride quality will also become extremely harsh.
How It Affects Your Speedometer
Your car's speedometer is calibrated to the exact diameter of the factory tyres. It calculates your speed based on how many revolutions the wheel makes.
If you fit a larger tyre, the wheel travels a longer distance per revolution. Because the car's computer doesn't know this, your speedometer will read slower than your actual physical speed. This can easily lead to unintentional speeding tickets on the highway!
Our calculator provides exactly what your true speed will be when the dashboard reads 100 km/h. Learn more about Tyre Codes and Sizing.