235/50R18 tire size — the same height as a 305-section 20
A crossover and premium-estate size whose closest neighbour by diameter is a rear tire from a very different kind of car.
Metric notation · Performance and ultra-high performance
- Overall diameter
- 27.25 in
- 692 mm
- Section width
- 9.25 in
- 235 mm
- Sidewall height
- 4.63 in
- 118 mm
- Aspect ratio
- 50%
- sidewall as a share of width
- Wheel diameter
- 18 in
- the hole in the middle
- Circumference
- 85.6 in
- 2175 mm
- Revolutions per mile
- 740.1
- geometric, not measured
- Revolutions per km
- 459.9
- geometric, not measured
- Typical load index
- 88–104
- 1235–1984 lb per tire
Low-profile sizes hold less air for their width, so the same vehicle weight needs a higher reference inflation. Extra Load construction is common in this class, and that is what lifts the index band — not any change in the casing size.
The load-index range shown is the band this CLASS of size is typically produced in — not a list of what is in stock for this exact size today. Load index and speed symbol are printed on the sidewall of the specific tire you are holding, and the required minimum is on the placard of the specific vehicle you are fitting. Read both.
Nearest real sizes in imperial notation, same wheel
- 33x12.50R1833.00 in tall+5.75 in
- 35x12.50R1835.00 in tall+7.75 in
- 37x12.50R1837.00 in tall+9.75 in
Compare any two sizes, including ones this site has no page for, in the comparison tool.
Platforms recorded with this size
Mid-size crossovers, premium estates and a number of all-wheel-drive saloons use this size, which sits at the point where 18-inch wheels stop being a performance choice and start being a practicality one.
Two tires that could not look less alike
305/30R20 measures 27.20 in. This size measures 27.25 in. The gap is 0.17%.
The section widths are 12.01 in and 9.25 in — a difference of 2.76 in, which is wider than several whole tires in the passenger part of this catalogue. The sidewalls are 3.60 in and 4.63 in. One is a rear tire from a wide-bodied performance car; the other goes on the front of a family crossover.
They roll identically. Nothing that counts wheel revolutions could distinguish them, which is a useful thing to keep in mind when a diameter match is presented as an equivalence.
The 27-inch neighbourhood
235/55R17 sits 0.07 in below at 27.18 in. The casing is the same 9.25 in across, the wheel is an inch smaller, and the aspect ratio has been raised by five points to compensate. That is the plus-one relationship performed cleanly, and the two sizes appear on the same vehicles in adjacent trim levels.
255/45R18 is 0.22 in below at 27.04 in on the same wheel, gaining 0.79 in of section and losing some sidewall. 215/65R16 is 0.25 in below at 27.00 in, two wheel sizes away.
What the aspect ratio is doing
At 235 mm, five points of aspect ratio is 0.93 in of diameter — one step below this size sits 235/45R18 at 26.33 in, and one step below that, 235/40R18 at 25.40 in. The same five points on a 195 mm casing would be worth about four-fifths as much. The aspect ratio reference explains why the same two digits mean different amounts of rubber on different widths.
Where the 12.01 in figure comes from
The 305/30R20 above is 12.01 in wide because 305 mm converts to that, but section width is the widest point of the inflated casing including the sidewall bulge — not the tread. On a very wide casing the gap between the two is substantial, and comparing a section width against a measured tread width is comparing different quantities. The section width vs tread width reference sets out what each one describes, and the comparison tool handles the rest of the geometry.
Related
- 235/55R17 vs 235/50R18
- 33x12.50R1833.00 in tall
- 35x12.50R1835.00 in tall
- 37x12.50R1837.00 in tall
Class: Performance and ultra-high performance. Every figure above is computed from the size code, not stored — see how these numbers are calculated.