245/55R18 vs 235/45R20
235/45R20 is 0.28 in (7.2 mm) shorter than 245/55R18, a −0.99% diameter difference. With the speedometer set for 245/55R18, an indicated 60 mph is 59.4 mph on 235/45R20.
Is this a safe swap?
Diameter difference −0.99%: under 1%
By overall diameter alone, 235/45R20 is a near match for 245/55R18; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.
| Measurement | 245/55R18 | 235/45R20 | Difference | % diff |
|---|---|---|---|---|
| Overall diameter | 28.61 in (726.7 mm) | 28.33 in (719.5 mm) | −0.28 in (−7.2 mm) | −0.99% |
| Sidewall height | 5.31 in (134.8 mm) | 4.16 in (105.8 mm) | −1.14 in (−29.0 mm) | −21.52% |
| Section width | 9.65 in (245.0 mm) | 9.25 in (235.0 mm) | −0.39 in (−10.0 mm) | −4.08% |
| Circumference | 89.88 in (2,283.0 mm) | 88.99 in (2,260.4 mm) | −0.89 in (−22.6 mm) | −0.99% |
| Revolutions per mile | 705 | 712 | +7 | +1.00% |
| Indicated | Actual on 245/55R18 | Actual on 235/45R20 | Difference |
|---|---|---|---|
| 30 mph | 30.0 mph | 29.7 mph | −0.3 mph |
| 60 mph | 60.0 mph | 59.4 mph | −0.6 mph |
| 75 mph | 75.0 mph | 74.3 mph | −0.7 mph |
Ride-height change: 235/45R20 lowers the vehicle by 0.14 in (3.6 mm) at the axle (half the −7.2 mm diameter difference).
235/45R20 is 0.28 in shorter than 245/55R18 and 10 mm narrower, a 0.99% difference in overall diameter.
With the speedometer calibrated for 245/55R18, an indicated 60 mph is actually 59.4 mph on 235/45R20, and revolutions per mile change from 705 to 712.
235/45R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 245/55R18.
Size pages
Other comparisons with 245/55R18
- 225/70R16 vs 245/55R18
- 245/65R16 vs 245/55R18
- 215/75R16 vs 245/55R18
- 235/70R16 vs 245/55R18
- 255/65R16 vs 245/55R18
- 225/65R17 vs 245/55R18
- 245/60R17 vs 245/55R18
- 245/50R18 vs 245/55R18
Other comparisons with 235/45R20
- 285/45R18 vs 235/45R20
- 235/55R18 vs 235/45R20
- 265/50R18 vs 235/45R20
- 235/50R19 vs 235/45R20
- 295/40R19 vs 235/45R20
- 265/45R19 vs 235/45R20
- 295/35R20 vs 235/45R20
- 235/45R20 vs 265/40R20
Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.