235/45 R17 vs 235/40 R18

235/40 R18 stays within the configured tolerance for 235/45 R17: +0.3% diameter and +0.3% speedometer effect.

Fitment verdict

235/40 R18 stays within the configured tolerance for 235/45 R17: +0.3% diameter and +0.3% speedometer effect.

Metric	This size: 235/45 R17	Alternative: 235/40 R18	Difference	Verdict
Overall diameter	25.33 in	25.40 in	+0.3%	Within tolerance
Section width	9.25 in	9.25 in	0.00 in	Computed difference
Sidewall height	4.16 in	3.70 in	-0.46 in	Computed difference
Circumference	79.57 in	79.80 in	+0.3%	Within tolerance
Speedo	0.0%	+0.3%	+0.3%	Within tolerance

Current tireLooks valid

New tireLooks valid

Market

Units

✓ Within toleranceDiameter +0.3% (+0.07 in) · US (~3%)

Diameter+0.3%+0.07 in

Speedo @ 60+0.3%60 mph → 60.2 mph

Sidewall-0.46 inWidth +0.00 in

How this result is calculated

Computed from nominal tire-size geometry: diameter, circumference and speedometer error. It does not check wheel-arch, suspension or brake clearance.

235/45 R17 235/40 R18 · Within tolerance

Use this size when shopping: 235/40 R18

Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.

Size	Diameter	Speedo @ 100
−1″ `215/55R16`	-0.1%	-0.1%
OE `235/45R17`	+0.0%	+0.0%
+1″ `155/60R18`	-0.0%	-0.0%
+2″ `145/55R19`	-0.2%	-0.2%

What changed

Reviewed deterministic geometry, load/speed references, sitemap inclusion and localized page shell.