305/30R20 vs 315/30R20
315/30R20 is a safe swap for 305/30R20 by the usual ±3% rule: the diameter differs by +0.87%.
Speedometer and odometer
With 315/30R20 on a car calibrated for 305/30R20, the speedometer reads 59.5 mph when you're really doing 60, and the odometer under-counts by 0.9%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.3 mph |
| 45 mph | 45.4 mph |
| 60 mph | 60.5 mph |
| 70 mph | 70.6 mph |
| 80 mph | 80.7 mph |
Other sizes close to 305/30R20
- 305/30R20 vs 255/40R19-0.64%
- 305/30R20 vs 245/40R20+1.88%
- 305/30R20 vs 245/35R20-1.66%
- 305/30R20 vs 255/35R20-0.65%
- 305/30R20 vs 275/35R20+1.37%
- 305/30R20 vs 255/40R20+3.04%
- 305/30R20 vs 225/45R19-0.85%
- 305/30R20 vs 235/45R19+0.45%
- 305/30R20 vs 285/35R20+2.39%
- 305/30R20 vs 285/30R20-1.74%
- 305/30R20 vs 275/30R20-2.60%
- 305/30R20 vs 265/35R20+0.36%
Questions
Can I replace 305/30R20 with 315/30R20?
315/30R20 is a safe swap for 305/30R20 by the usual ±3% rule: the diameter differs by +0.87%.
What's the difference between 305/30R20 and 315/30R20?
315/30R20 is 0.24" taller and 10 mm wider; the sidewall is +0.12". At an indicated 60 mph you'd actually be doing 60.5 mph.
Will 315/30R20 fit on 305/30R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 315 mm tire and the fender clearance.