235/40 R18 vs 205/65 R15

205/65 R15 stays within the configured tolerance for 235/40 R18: +0.4% diameter and +0.4% speedometer effect.

Fitment verdict

205/65 R15 stays within the configured tolerance for 235/40 R18: +0.4% diameter and +0.4% speedometer effect.

Metric	This size: 235/40 R18	Alternative: 205/65 R15	Difference	Verdict
Overall diameter	25.40 in	25.49 in	+0.4%	Within tolerance
Section width	9.25 in	8.07 in	-1.18 in	Computed difference
Sidewall height	3.70 in	5.25 in	+1.55 in	Computed difference
Circumference	79.80 in	80.09 in	+0.4%	Within tolerance
Speedo	0.0%	+0.4%	+0.4%	Within tolerance

Current tireLooks valid

New tireLooks valid

Market

Units

✓ Within toleranceDiameter +0.4% (+0.09 in) · US (~3%)

Diameter+0.4%+0.09 in

Speedo @ 60+0.4%60 mph → 60.2 mph

Sidewall+1.55 inWidth -1.18 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.

235/40 R18 205/65 R15 · Within tolerance

Use this size when shopping: 205/65 R15

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

Size	Diameter	Speedo @ 100
−1″ `305/35R17`	+0.0%	+0.0%
OE `235/40R18`	+0.0%	+0.0%
+1″ `125/65R19`	-0.0%	-0.0%
+2″ `125/55R20`	+0.0%	+0.0%

What changed

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