245/35R21 vs 305/30R21
305/30R21 is a safe swap for 245/35R21 by the usual ±3% rule: the diameter differs by +1.63%.
Speedometer and odometer
With 305/30R21 on a car calibrated for 245/35R21, 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 245/35R21
- 245/35R21 vs 245/40R20-0.13%
- 245/35R21 vs 275/35R20-0.62%
- 245/35R21 vs 285/35R20+0.37%
- 245/35R21 vs 275/35R21+2.98%
- 245/35R21 vs 295/35R21+4.97%
- 245/35R21 vs 255/40R21+4.61%
- 245/35R21 vs 265/35R21+1.99%
- 245/35R21 vs 325/30R21+3.33%
- 245/35R21 vs 255/35R21+0.99%
- 245/35R21 vs 315/30R21+2.48%
- 245/35R21 vs 285/35R21+3.97%
- 245/35R21 vs 245/40R21+3.48%
Questions
Can I replace 245/35R21 with 305/30R21?
305/30R21 is a safe swap for 245/35R21 by the usual ±3% rule: the diameter differs by +1.63%.
What's the difference between 245/35R21 and 305/30R21?
305/30R21 is 0.45" taller and 60 mm wider; the sidewall is +0.23". At an indicated 60 mph you'd actually be doing 61.0 mph.
Will 305/30R21 fit on 245/35R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 305 mm tire and the fender clearance.