215/55 R16 vs 235/40 R18

235/40 R18 stays within the configured tolerance for 215/55 R16: +0.4% diameter and +0.4% speedometer effect.

Fitment verdict

235/40 R18 stays within the configured tolerance for 215/55 R16: +0.4% diameter and +0.4% speedometer effect.

Metric	This size: 215/55 R16	Alternative: 235/40 R18	Difference	Verdict
Overall diameter	25.31 in	25.40 in	+0.4%	Within tolerance
Section width	8.46 in	9.25 in	+0.79 in	Computed difference
Sidewall height	4.66 in	3.70 in	-0.95 in	Computed difference
Circumference	79.52 in	79.80 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-0.95 inWidth +0.79 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.

215/55 R16 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″ `175/75R15`	+0.1%	+0.1%
OE `215/55R16`	+0.0%	+0.0%
+1″ `235/45R17`	+0.1%	+0.1%
+2″ `265/35R18`	-0.0%	-0.0%

What changed

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