235/50R20 vs 305/40R20
305/40R20 is a safe swap for 235/50R20 by the usual ±3% rule: the diameter differs by +1.21%.
Speedometer and odometer
With 305/40R20 on a car calibrated for 235/50R20, the speedometer reads 59.3 mph when you're really doing 60, and the odometer under-counts by 1.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.4 mph |
| 45 mph | 45.5 mph |
| 60 mph | 60.7 mph |
| 70 mph | 70.8 mph |
| 80 mph | 81.0 mph |
Other sizes close to 235/50R20
- 235/50R20 vs 235/55R19-0.26%
- 235/50R20 vs 245/45R20-1.95%
- 235/50R20 vs 255/45R20-0.74%
- 235/50R20 vs 255/50R19-0.73%
- 235/50R20 vs 275/40R20-2.02%
- 235/50R20 vs 255/50R20+2.69%
- 235/50R20 vs 265/50R20+4.04%
- 235/50R20 vs 245/50R20+1.35%
- 235/50R20 vs 275/45R20+1.68%
- 235/50R20 vs 235/55R20+3.16%
- 235/50R20 vs 255/40R20-4.17%
- 235/50R20 vs 265/45R20+0.47%
Questions
Can I replace 235/50R20 with 305/40R20?
305/40R20 is a safe swap for 235/50R20 by the usual ±3% rule: the diameter differs by +1.21%.
What's the difference between 235/50R20 and 305/40R20?
305/40R20 is 0.35" taller and 70 mm wider; the sidewall is +0.18". At an indicated 60 mph you'd actually be doing 60.7 mph.
Will 305/40R20 fit on 235/50R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 305 mm tire and the fender clearance.