What do Tire Numbers Mean?
To use this calculator, you need to understand the code on your tire sidewall (e.g., 225/50R17). It is not just a random number; it is a mathematical formula for the tire's physical size.
- 225 (Width): The width of the tire in millimeters from sidewall to sidewall.
- 50 (Aspect Ratio): The height of the sidewall as a percentage of the width. (50% of 225mm).
- 17 (Rim): The diameter of the metal wheel in inches.
How Speedometer Error Happens
Your car's speedometer doesn't measure speed directly; it counts how many times the wheels rotate. If you put on larger tires, they cover more ground per rotation, meaning you are moving faster than the gauge shows.
If the new tire is 5% larger, your speedometer reads 60 mph, but you are actually going 63 mph. You risk speeding tickets.
If the tire is smaller, the speedometer reads higher than your actual speed. Your engine revs higher, wasting fuel.
Our calculator checks the percentage difference. If the result exceeds 3%, modern cars may experience issues with ABS braking systems and Traction Control sensors, as they rely on precise wheel rotation data.
Comparison: Stock vs. New
When "Plus Sizing" (using larger rims), you must reduce the tire profile (aspect ratio) to keep the overall diameter the same.
| Measurement | Stock (Example) | New (Example) | Difference |
|---|---|---|---|
| Specification | 205/55R16 | 225/45R17 | - |
| Diameter | 631.9 mm | 634.3 mm | +0.4% (Safe) |
| Sidewall | 112.7 mm | 101.2 mm | -10.2% (Stiffer Ride) |
| Speedometer | 60 mph | 60.2 mph | Negligible |
Frequently Asked Questions
Can I change my tire width?
Yes, you can usually go wider (e.g., 205 to 215) without issues, provided they don't rub against the suspension or fenders. Wider tires offer better grip but may increase fuel consumption.
What is the maximum safe difference?
Most mechanics and manufacturers recommend staying within ±3% of the original diameter. Trucks and off-road vehicles may tolerate larger changes, but recalibration is suggested.
Disclaimer
This AI Tire Size Calculator provides mathematical estimates based on standard tire specifications. Actual tire dimensions vary slightly by brand and model. This tool does not account for physical clearance (rubbing against fenders/brakes). Always consult a tire professional before purchasing.