Tyre Size Converter / Upsize Calculator
Many car and bike owners think about upgrading their tyre size for better grip, better looks or improved ride quality. But the wrong tyre size can affect your speedometer reading, mileage, handling and even suspension life. The Tyre Size Converter helps you compare your old tyre size with the new one and instantly shows the difference in diameter, height and speedometer impact.
This guide explains how to use the tool properly and how to understand the results.
What the Tyre Size Converter Does
The tool compares your old tyre size and new tyre size, then calculates:
- Overall diameter (old vs new)
- Difference in height
- Percentage difference in tyre size
- Approximate speedometer error
- Effect of upsize or downsize
This helps you choose a safe and suitable tyre upgrade.
How Tyre Size Format Works
Tyre sizes follow a simple pattern:
Example: 205/55R16
- 205 → Tyre width in mm
- 55 → Aspect ratio (height is 55% of width)
- R16 → Rim diameter in inches
The tool uses this formula to calculate tyre height and diameter.
Inputs You Need to Enter
1. Old Tyre Size
Enter your current tyre size exactly as written on the sidewall.
Example: 205/55R16, 185/65R15, 110/70R17 (for bikes).
2. New Tyre Size
Enter the tyre size you want to upgrade to.
Example: 215/50R17, 195/60R15, etc.
How to Use the Tool (Step-by-step)
- Type your Old Tyre Size in the box.
- Enter the New Tyre Size you want to check.
- Click Compare.
- The tool instantly shows:
- Old tyre diameter
- New tyre diameter
- Difference in mm
- Difference in percentage
- Speedometer impact
This helps you decide whether the new tyre size is safe for your vehicle.
Example Tyre Upsize Calculation
Old size: 205/55R16
New size: 215/50R17
The tool will calculate:
- Increase or decrease in diameter (in mm)
- Height difference
- Percentage size change
- Speedometer reading difference
If the percentage difference is too high, the upsize is not recommended.
Most tyre experts prefer keeping the difference within ±3% for safety and comfort.
Why This Tool Is Useful
- Helps avoid unsafe or incorrect tyre upgrades
- Shows real effects of upsize on handling and mileage
- Prevents speedometer errors
- Helps choose a rim upgrade safely
- Useful for car owners, bike riders and modification enthusiasts
Things to Keep in Mind Before Upsizing
- A higher diameter tyre may reduce mileage
- A wider tyre improves grip but may reduce pickup
- Too much upsize can touch the wheel arch or suspension
- Speedometer may over-read or under-read
- Always check recommended tyre sizes for your vehicle model
Frequently Asked Questions
Q. What tyre size difference is safe?
Most experts recommend staying within ±3% diameter difference.
Q. Will tyre upsize increase mileage?
Usually no. Bigger tyres increase rolling resistance and may reduce mileage.
Q. Can I use this tool for bikes?
Yes. The calculator works for both cars and motorcycles.
Q. Why does the speedometer get affected?
A bigger tyre covers more distance per rotation, so the speedometer may show lower or higher readings.
Conclusion
The Tyre Size Converter is an essential tool for anyone planning a tyre upgrade. By comparing your old and new tyre sizes, you can instantly see the size difference, height change and speedometer impact. This helps you avoid unsafe or incorrect upsizing and ensures your vehicle maintains proper handling, comfort and performance. Always check your tyre size using this tool before making any upgrade decision.
