235/45R18 vs 235/50R18
Diameter +3.51% · Speedo at 60 mph reads 62.1 mph actual · Ground clearance +11.8 mm
Caution — review clearance and calibration
The 3–5% diameter difference may affect speedometer accuracy and ABS calibration noticeably. Fitment is possible on many vehicles but should be verified for wheel-well clearance and approved by a tire professional.
Speedometer effect
When the vehicle's speedometer (calibrated to 235/45R18) reads 60 mph, the actual speed with 235/50R18 mounted is:
Speedometer error: +3.52% · Odometer reads high by 3.52%
Full comparison
| Measurement | 235/45R18 | 235/50R18 | Delta |
|---|---|---|---|
| Overall diameter | 26.33" | 27.25" | +3.51% |
| Section width | 235 mm | 235 mm | +0 mm |
| Sidewall height | 105.75 mm | 117.5 mm | +11.75 mm |
| Rim diameter | 18" | 18" | +0" |
| Circumference | 2101 mm | 2175 mm | +74 mm |
| Revs / mile | 766 | 740 | -26 |
| Ground clearance change | +11.8 mm | ||
Questions about this swap
What is the diameter difference between 235/45R18 and 235/50R18?
235/50R18 is 3.51% larger in overall diameter than 235/45R18 — a difference of 23.5 mm (0.93 inches).
How does 235/50R18 affect the speedometer if the car was calibrated for 235/45R18?
When the speedometer reads 60 mph (calibrated for 235/45R18), the actual speed with 235/50R18 is 62.1 mph — an error of +3.52%.
Is it safe to replace 235/45R18 with 235/50R18?
Caution — review clearance and calibration. The 3–5% diameter difference may affect speedometer accuracy and ABS calibration noticeably. Fitment is possible on many vehicles but should be verified for wheel-well clearance and approved by a tire professional.
All calculations use standard ETRTO formulas. Confirm fitment with a qualified tire professional and your vehicle's door-placard before purchasing.