245/40R15 vs 195/55R15
195/55R15 is outside the ±3% rule as a replacement for 245/40R15: the diameter differs by +3.21%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 195/55R15 on a car calibrated for 245/40R15, the speedometer reads 58.1 mph when you're really doing 60, and the odometer under-counts by 3.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.0 mph |
| 45 mph | 46.4 mph |
| 60 mph | 61.9 mph |
| 70 mph | 72.2 mph |
| 80 mph | 82.6 mph |
Other sizes close to 245/40R15
Questions
Can I replace 245/40R15 with 195/55R15?
195/55R15 is outside the ±3% rule as a replacement for 245/40R15: the diameter differs by +3.21%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 245/40R15 and 195/55R15?
195/55R15 is 0.73" taller and 50 mm narrower; the sidewall is +0.36". At an indicated 60 mph you'd actually be doing 61.9 mph.
Will 195/55R15 fit on 245/40R15 wheels?
Both use a 15" rim, so the wheel diameter matches; check the wheel's width range for a 195 mm tire and the fender clearance.