Practical tools for measured work
Alternative & Equivalent Tire Size Finder
Find standard tire sizes, including different wheel diameters, that keep overall diameter within a chosen tolerance of a starting size.
e.g. 225/45R18
Maximum overall-diameter change to allow
| Alternative size | Wheel diameter | Overall diameter | Diameter change |
|---|---|---|---|
| 285/40R17 | 17 in | 659.8 mm | +0.02% |
| 295/30R19 | 19 in | 659.6 mm | -0.02% |
| 195/65R16 | 16 in | 659.9 mm | +0.03% |
| 355/25R19 | 19 in | 660.1 mm | +0.06% |
| 175/65R17 | 17 in | 659.3 mm | -0.06% |
| 325/35R17 | 17 in | 659.3 mm | -0.06% |
| 305/25R20 | 20 in | 660.5 mm | +0.12% |
| 155/65R18 | 18 in | 658.7 mm | -0.15% |
| 185/55R18 | 18 in | 660.7 mm | +0.15% |
| 215/35R20 | 20 in | 658.5 mm | -0.18% |
| 255/30R20 | 20 in | 661 mm | +0.2% |
| 315/40R16 | 16 in | 658.4 mm | -0.2% |
| 255/35R19 | 19 in | 661.1 mm | +0.21% |
| 255/40R18 | 18 in | 661.2 mm | +0.23% |
| 335/30R18 | 18 in | 658.2 mm | -0.23% |
| 255/45R17 | 17 in | 661.3 mm | +0.24% |
| 195/45R19 | 19 in | 658.1 mm | -0.24% |
| 255/50R16 | 16 in | 661.4 mm | +0.26% |
| 175/50R19 | 19 in | 657.6 mm | -0.32% |
| 205/55R17 | 17 in | 657.3 mm | -0.36% |
| 205/50R18 | 18 in | 662.2 mm | +0.38% |
| 225/40R19 | 19 in | 662.6 mm | +0.44% |
| 225/50R17 | 17 in | 656.8 mm | -0.44% |
| 285/35R18 | 18 in | 656.7 mm | -0.45% |
| 165/70R17 | 17 in | 662.8 mm | +0.47% |
| 285/45R16 | 16 in | 662.9 mm | +0.49% |
| 165/45R20 | 20 in | 656.5 mm | -0.49% |
| 155/50R20 | 20 in | 663 mm | +0.5% |
| 185/40R20 | 20 in | 656 mm | -0.56% |
| 295/35R18 | 18 in | 663.7 mm | +0.61% |
| 295/25R20 | 20 in | 655.5 mm | -0.64% |
| 195/40R20 | 20 in | 664 mm | +0.65% |
| 165/55R19 | 19 in | 664.1 mm | +0.67% |
| 165/60R18 | 18 in | 655.2 mm | -0.68% |
| 345/30R18 | 18 in | 664.2 mm | +0.68% |
| 155/75R17 | 17 in | 664.3 mm | +0.7% |
| 345/25R19 | 19 in | 655.1 mm | -0.7% |
| 215/60R16 | 16 in | 664.4 mm | +0.71% |
| 245/30R20 | 20 in | 655 mm | -0.71% |
| 355/35R16 | 16 in | 654.9 mm | -0.73% |
How it works
Starting point: enter one tire size you already have (in 225/45R18 notation) and a tolerance. This tool searches standard width, aspect-ratio and wheel-diameter combinations - not just the two sizes you already know - and lists every one whose overall (rolling) diameter stays within that tolerance of your starting size.
Why this differs from a two-size comparison: if you already have both sizes in mind, a side-by-side comparison tells you the difference between them. This tool works the other way: starting from one size, it finds which other sizes - including ones on a different wheel diameter - are close enough to be a plausible substitute.
Results are sorted by closeness to your starting diameter and capped at the 40 closest matches. A tighter tolerance (1-2%) keeps the speedometer and gearing effect negligible; a wider one (3%+) opens up more plus-size or downsize options at the cost of a bigger speedometer and rolling-circumference change.
FAQ
Does every listed size actually exist?
Will a size within tolerance definitely fit my car?
What tolerance should I use?
Related tools
Tire Size Calculator
Compare two tyre sizes side by side - diameter, sidewall, circumference and speedometer effect.
Wheel Offset Calculator
Compare a current and proposed wheel/tyre setup and see exactly how the geometry changes.
Wheel Spacer Calculator
See how a wheel spacer changes your effective offset and how far the wheel moves outward.
Scrub Radius Calculator
See how much a wheel offset or spacer change shifts your scrub radius from a known baseline.