Tire Size Calculator
Compare tire sizes and calculate the impact on speedometer accuracy, ground clearance, and overall diameter.
Original Tire Size
First number in tire size (e.g., 225/55R17)
Second number - sidewall height as % of width
Last number - wheel diameter
New Tire Size
Size Difference
0%
Original Diameter
0"
New Diameter
0"
Diameter Change
0"
Speedometer Impact
When speedo shows 60 mph
0 mph actual
When speedo shows 70 mph
0 mph actual
Speedometer Error
0%
Other Effects
Ground Clearance Change
0"
Revs per Mile (Original)
0
Revs per Mile (New)
0
Tire Dimensions
Original Sidewall Height
0"
New Sidewall Height
0"
Original Circumference
0"
New Circumference
0"
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Understanding Tire Sizes
Reading a Tire Size (e.g., 225/55R17):
- 225: Section width in millimeters
- 55: Aspect ratio (sidewall height = 55% of width)
- R: Radial construction
- 17: Rim diameter in inches
Safe Size Changes:
- Keep overall diameter within 3% of original
- Larger changes affect speedometer, ABS, traction control
- Check for clearance with suspension and fenders
- Consider load rating and speed rating requirements
Plus Sizing (Larger Wheels):
- Plus 1: +1" wheel, shorter sidewall (e.g., 225/55R17 to 225/50R18)
- Plus 2: +2" wheel, even shorter sidewall
- Maintain similar overall diameter for accuracy
- Shorter sidewalls = stiffer ride, better handling