305/70R17 vs 315/70R17
315/70R17 is a safe swap for 305/70R17 by the usual ±3% rule: the diameter differs by +1.63%.
Speedometer and odometer
With 315/70R17 on a car calibrated for 305/70R17, the speedometer reads 59.0 mph when you're really doing 60, and the odometer under-counts by 1.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.5 mph |
| 45 mph | 45.7 mph |
| 60 mph | 61.0 mph |
| 70 mph | 71.1 mph |
| 80 mph | 81.3 mph |
Other sizes close to 305/70R17
Questions
Can I replace 305/70R17 with 315/70R17?
315/70R17 is a safe swap for 305/70R17 by the usual ±3% rule: the diameter differs by +1.63%.
What's the difference between 305/70R17 and 315/70R17?
315/70R17 is 0.55" taller and 10 mm wider; the sidewall is +0.28". At an indicated 60 mph you'd actually be doing 61.0 mph.
Will 315/70R17 fit on 305/70R17 wheels?
Both use a 17" rim, so the wheel diameter matches; check the wheel's width range for a 315 mm tire and the fender clearance.