Tire size
235/45 R18
Full dimensions and a live comparison calculator for the 235/45 R18 tire size.
Overall diameter
668.7 mm
26.33″
Sidewall height
105.8 mm
Circumference
2.101 m
Revs / km
476.0
Section width
235 mm
Aspect ratio
45%
Rim diameter
18″
457.2 mm
Radius
334.4 mm
What does 235/45 R18 mean?
The 235 is the section width in millimetres, measured sidewall to sidewall. The 45 is the aspect ratio — sidewall height as a percentage of width, so the sidewall here is 105.8 mm. The R18 means a radial-construction tire designed for a 18-inch wheel rim. Together these give an overall diameter of 669 mm.
Compare 235/45 R18 with another size
Current Tire
New Tire
Ground line · scaled comparison
Not Recommended
Over 5% — speedometer & ABS may misread
Diameter change
-34.4 mm
-5.14%
Speedometer at 100
94.9 km/h
-5.14% error
Ground clearance
-17.2 mm
ride height delta
Sidewall change
-4.5 mm
revs/km: 501.8
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/compare/235-45-r18-vs-225-45-r17Common alternatives to 235/45 R18
These sizes are within a few percent overall diameter — usually safe on the same vehicle from a speedometer-error standpoint.
Compare 235/45 R18 with popular upgrades
Plus-size upgrades from 235/45 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.