Tire size
215/40 R18
Full dimensions and a live comparison calculator for the 215/40 R18 tire size.
Overall diameter
629.2 mm
24.77″
Sidewall height
86.0 mm
Circumference
1.977 m
Revs / km
505.9
Section width
215 mm
Aspect ratio
40%
Rim diameter
18″
457.2 mm
Radius
314.6 mm
What does 215/40 R18 mean?
The 215 is the section width in millimetres, measured sidewall to sidewall. The 40 is the aspect ratio — sidewall height as a percentage of width, so the sidewall here is 86.0 mm. The R18 means a radial-construction tire designed for a 18-inch wheel rim. Together these give an overall diameter of 629 mm.
Compare 215/40 R18 with another size
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
+5.1 mm
0.81%
Speedometer at 100
100.8 km/h
+0.81% error
Ground clearance
+2.5 mm
ride height delta
Sidewall change
+15.3 mm
revs/km: 501.8
Permalink for this comparison:
/compare/215-40-r18-vs-225-45-r17Common alternatives to 215/40 R18
These sizes are within a few percent overall diameter — usually safe on the same vehicle from a speedometer-error standpoint.
Compare 215/40 R18 with popular upgrades
Plus-size upgrades from 215/40 R18
Fitment safety note
Overall diameter, speedometer error and circumference are only part of the picture. Physical clearance, wheel offset (ET), hub bore, suspension geometry, load index and your manufacturer's recommendation all decide whether a size is truly safe on your car. Always cross-check with the vehicle manual or a qualified fitter before changing tire size.