Enter stock and new sizes. See overall diameter, sidewall, Δ%, and speedometer error from public tire geometry.
A size such as 225/65R17 is the section width in millimetres, the aspect ratio, and the rim diameter in inches. Overall diameter (mm) = rim × 25.4 + 2 × sidewall. Sidewall height (mm) = section × aspect / 100.
Actual speed = indicated speed × new overall diameter / stock overall diameter. Percent error = (new diameter − stock diameter) / stock diameter.
Stock 225/65R17 has sidewall 146.25 mm and overall diameter 724.3 mm. New 235/60R18 has sidewall 141 mm and overall diameter 739.2 mm. Diameter change +14.9 mm (+2.06 %). At an indicated 60 km/h, actual speed is 61.2 km/h. Speedometer error +2.06 %.
225/65R17 decodes as section 225 mm, aspect 65, rim 17 in.
235/60R18 decodes as section 235 mm, aspect 60, rim 18 in.
Outlines are drawn at true scale and share a ground line.
Diameter change
+14.9 mm
Δ%
+2.06 %
实际速度
61.2 km/h
车速表误差
+2.06 %
| 225/65R17 | 235/60R18 | Δ | |
|---|---|---|---|
| Section width | 225 mm | 235 mm | +10 mm |
| Sidewall height | 146.25 mm | 141 mm | -5.25 mm |
| 总直径 | 724.3 mm | 739.2 mm | +14.9 mm |
| 周长 | 2,275.5 mm | 2,322.3 mm | +46.8 mm |
| 转数 | 439.5 /km | 430.6 /km | -8.9 /km |
Estimates from public tire geometry. Not a fitment certificate and not a legal speedometer certification.
Enter a rim width and an offset (ET) for each wheel. The sketch aligns the hub faces and shows the change in outer lip position. This is relative Δ poke, not fender clearance for a specific car.
Outer position from the hub face (mm) = (rim width in inches × 25.4) / 2 − offset (mm). Relative Δ poke = new − stock. Positive means the new lip sits farther out.
Example wheels, not a car: a 7.5 in rim at ET 45 sits 50.25 mm from the hub face. A 8.5 in rim at ET 35 sits 72.95 mm. Relative Δ poke is +22.7 mm.