235/45R18 vs 245/40R18 Tire Comparison
235/45R18 has nominal diameter 26.3268 in; 245/40R18 has 25.7165 in. Diameter changes -2.318%; at indicated 60 mph the new nominal speed is 58.609 mph. Selected standard passenger and common truck/SUV tire sizes, not a verified market-popularity ranking. Nominal dimensions do not guarantee vehicle fitment.
235/45R18 vs 245/40R18 Tire Comparison reference last updated · reference source
Loading calculator…
Dated static reference; no live data is fetched. Verify current source values and assumptions before relying on results.
What this tool does
235/45R18 has nominal diameter 26.3268 in; 245/40R18 has 25.7165 in. Diameter changes -2.318%; at indicated 60 mph the new nominal speed is 58.609 mph. Selected standard passenger and common truck/SUV tire sizes, not a verified market-popularity ranking. Nominal dimensions do not guarantee vehicle fitment.
How to use the 235/45R18 vs 245/40R18 Tire Comparison
- Check Tire width (mm): 235.
- Check Tire aspect ratio (%): 45.
- Check Tire rim diameter (inches): 18.
- Check Tire B width (mm): 245.
- Check Tire B aspect ratio (%): 40.
- Check Tire B rim diameter (inches): 18.
- Check Indicated speed (mph): 60.
- Review the 235/45R18 vs 245/40R18 Tire Comparison result and its exact-value comparison table.
- Verify assumptions before applying the result.
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
235/45R18 vs 245/40R18 Tire Comparison: Tire width (mm) = 235; Tire aspect ratio (%) = 45; Tire rim diameter (inches) = 18; Tire B width (mm) = 245; Tire B aspect ratio (%) = 40; Tire B rim diameter (inches) = 18; Indicated speed (mph) = 60. 235/45R18 has nominal diameter 26.3268 in; 245/40R18 has 25.7165 in. Diameter changes -2.318%; at indicated 60 mph the new nominal speed is 58.609 mph. Selected standard passenger and common truck/SUV tire sizes, not a verified market-popularity ranking. Nominal dimensions do not guarantee vehicle fitment.
Inputs
- Tire width (mm)235
- Tire aspect ratio (%)45
- Tire rim diameter (inches)18
- Tire B width (mm)245
- Tire B aspect ratio (%)40
- Tire B rim diameter (inches)18
- Indicated speed (mph)60
Result
- Diameter difference (%)-2.32
- Actual speed (mph)58.61
- Ground clearance change-0.31 in
235/45R18 versus 245/40R18
| Measurement | Original tire | New tire |
|---|---|---|
| Diameter (in) | 26.326771653543307 | 25.716535433070867 |
| Sidewall (in) | 4.163385826771654 | 3.8582677165354333 |
| Circumference (in) | 82.70799241950766 | 80.79087879231705 |
| Revolutions/mile | 766.0686488269275 | 784.2469465256681 |
| Speed at indicated 30 mph | 30 | 29.30462090623598 |
| Speed at indicated 45 mph | 45 | 43.956931359353966 |
| Speed at indicated 60 mph | 60 | 58.60924181247196 |
| Speed at indicated 70 mph | 70 | 68.37744878121728 |
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
Diameter difference is -0.6102 inches (-2.318%).
4.1634 and 3.8583 inches respectively.
Nominal actual speed becomes 58.609 mph if calibrated to 235/45R18.
766.07 versus 784.25 geometric revolutions/mile.
This comparison cannot confirm fitment. Ground clearance changes -0.3051181102362204 in geometrically; verify wheel width, offsets, load/speed ratings and manufacturer requirements.