Tire Size Comparison Calculator
Compare exact geometric dimensions and speedometer changes for two tire sizes.
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What this tool does
Compare exact geometric dimensions and speedometer changes for two tire sizes. Assumes the speedometer was calibrated to the original tire. Does not check wheel offset, width or clearance.
How to use the Tire Size Comparison Calculator
- Enter or select tire width (mm).
- Enter or select tire aspect ratio (%).
- Enter or select tire rim diameter (inches).
- Enter or select tire b width (mm).
- Enter or select tire b aspect ratio (%).
- Enter or select tire b rim diameter (inches).
- Enter or select indicated speed (mph).
- Read the calculated result; change any measurement to compare alternatives.
Formula
difference%=(diameterB/diameterA−1)×100; actual speed=indicated speed×diameterB/diameterA
- width
- Tire width (mm)
- aspect
- Tire aspect ratio (%)
- rim
- Tire rim diameter (inches)
- widthB
- Tire B width (mm)
- aspectB
- Tire B aspect ratio (%)
- rimB
- Tire B rim diameter (inches)
- speed
- Indicated speed (mph)
Assumes the speedometer was calibrated to the original tire. Does not check wheel offset, width or clearance.
Worked example
For tire size comparison calculator, the following measurements illustrate the exact method: Tire width (mm): 225; Tire aspect ratio (%): 50; Tire rim diameter (inches): 17; Tire B width (mm): 235; Tire B aspect ratio (%): 45; Tire B rim diameter (inches): 17; Indicated speed (mph): 60.
Inputs
- Tire width (mm)225
- Tire aspect ratio (%)50
- Tire rim diameter (inches)17
- Tire B width (mm)235
- Tire B aspect ratio (%)45
- Tire B rim diameter (inches)17
- Indicated speed (mph)60
Result
- Diameter difference (%)-2.06
- Actual speed (mph)58.77
- Ground clearance change-0.27 in
Results explained
- Diameter difference (%)
- Diameter difference (%) from the formula above. Assumes the speedometer was calibrated to the original tire. Does not check wheel offset, width or clearance.
- Actual speed (mph)
- Actual speed (mph) from the formula above. Assumes the speedometer was calibrated to the original tire. Does not check wheel offset, width or clearance.
- Ground clearance change
- Ground clearance change from the formula above, expressed in in before metric conversion. Assumes the speedometer was calibrated to the original tire. Does not check wheel offset, width or clearance.
Frequently asked questions
difference%=(diameterB/diameterA−1)×100; actual speed=indicated speed×diameterB/diameterA
Use the tire sidewall markings, actual vehicle specifications or recorded fuel/price values required by the inputs. Do not mix US gallons and imperial gallons.
Assumes the speedometer was calibrated to the original tire. Does not check wheel offset, width or clearance.
Yes. Change the relevant size, price or efficiency while keeping the other inputs constant. Results update immediately.
No. Check manufacturer fitment, load and speed ratings, clearance and local requirements with a qualified technician.