225/40R18 vs 235/35R19
Diameter +1.55% · Speedo at 60 mph reads 60.9 mph actual · Ground clearance +5.0 mm
Generally safe — within the 3% tolerance
The diameter difference is ≤3%, which is the widely-accepted fitment tolerance for speedometer accuracy and ABS/traction-control calibration. Verify clearance and load rating with a tire professional before installing.
Speedometer effect
When the vehicle's speedometer (calibrated to 225/40R18) reads 60 mph, the actual speed with 235/35R19 mounted is:
Speedometer error: +1.55% · Odometer reads high by 1.55%
Full comparison
| Measurement | 225/40R18 | 235/35R19 | Delta |
|---|---|---|---|
| Overall diameter | 25.09" | 25.48" | +1.55% |
| Section width | 225 mm | 235 mm | +10 mm |
| Sidewall height | 90 mm | 82.25 mm | -7.75 mm |
| Rim diameter | 18" | 19" | +1" |
| Circumference | 2002 mm | 2033 mm | +31 mm |
| Revs / mile | 804 | 792 | -12 |
| Ground clearance change | +5.0 mm | ||
Questions about this swap
What is the diameter difference between 225/40R18 and 235/35R19?
235/35R19 is 1.55% larger in overall diameter than 225/40R18 — a difference of 9.9 mm (0.39 inches).
How does 235/35R19 affect the speedometer if the car was calibrated for 225/40R18?
When the speedometer reads 60 mph (calibrated for 225/40R18), the actual speed with 235/35R19 is 60.9 mph — an error of +1.55%.
Is it safe to replace 225/40R18 with 235/35R19?
Generally safe — within the 3% tolerance. The diameter difference is ≤3%, which is the widely-accepted fitment tolerance for speedometer accuracy and ABS/traction-control calibration. Verify clearance and load rating with a tire professional before installing.
All calculations use standard ETRTO formulas. Confirm fitment with a qualified tire professional and your vehicle's door-placard before purchasing.