235/55R17 tire size — geometry and its 18-inch counterpart
A compact-crossover fitment, and one half of a pairing that trades sidewall for wheel with nothing else changing.
Metric notation · Passenger touring
- Overall diameter
- 27.18 in
- 690 mm
- Section width
- 9.25 in
- 235 mm
- Sidewall height
- 5.09 in
- 129 mm
- Aspect ratio
- 55%
- sidewall as a share of width
- Wheel diameter
- 17 in
- the hole in the middle
- Circumference
- 85.4 in
- 2169 mm
- Revolutions per mile
- 742.1
- geometric, not measured
- Revolutions per km
- 461.1
- geometric, not measured
- Typical load index
- 82–99
- 1047–1709 lb per tire
A passenger tire's load index tracks its air volume, and volume tracks section width and sidewall height. Sizes in this class sit in the band that carries a typical two-tonne car with its rated payload across four tires.
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
- 32x11.50R1732.00 in tall+4.82 in
- 33x10.50R1733.00 in tall+5.82 in
- 33x12.50R1733.00 in tall+5.82 in
Compare any two sizes, including ones this site has no page for, in the comparison tool.
Platforms recorded with this size
Compact and mid-size crossovers in their smaller wheel options, plus a scattering of estates and all-wheel-drive saloons.
Same tread, one more inch of wheel
235/50R18 measures 27.25 in. This size measures 27.18 in. The difference is 0.07 in — 0.28%.
Section width is identical at 9.25 in. What changes is the split: 5.09 in of sidewall here against 4.63 in there, with the extra inch of wheel making up almost exactly the difference. This is what a manufacturer does when it wants two trim levels to look different and drive the same, and it is why both sizes appear on the same vehicles.
Its own wheel, from 45 to 60
| Size | Aspect | Diameter | Sidewall |
|---|---|---|---|
| 235/45R17 | 45 | 25.33 in | 4.16 in |
| 235/55R17 | 55 | 27.18 in | 5.09 in |
| 235/60R17 | 60 | 28.10 in | 5.55 in |
The gap from 45 to 55 is two steps and 1.85 in; from 55 to 60 it is one step and 0.93 in. The arithmetic is linear in the aspect number, which is exactly what makes a 5-point change predictable and a change of width plus aspect together not.
What matches it elsewhere
Three 255 mm sizes land within 0.15 in: 255/45R18 at 27.04 in, 255/40R19 at 27.03 in and 255/35R20 at 27.03 in. All three carry 0.79 in more section width and less sidewall, and all three belong to performance rather than crossover fitments.
215/65R16 is 0.17 in below at 27.00 in, coming at the same height from the opposite direction — narrower tread, deeper sidewall, smaller wheel.
The letters that share the size field
Most tires in this code are marked plainly with an R for radial construction, but the size field can also carry a service-type prefix or a ZR in place of the R, and neither alters a dimension. On a crossover fitment the prefix is the one worth noticing, because a P-metric casing and an LT-marked one of the same size are built and rated to different standards. The tire construction codes reference works through every letter that can appear there.
Related
- 235/55R17 vs 235/50R18
- 32x11.50R1732.00 in tall
- 33x10.50R1733.00 in tall
- 33x12.50R1733.00 in tall
Class: Passenger touring. Every figure above is computed from the size code, not stored — see how these numbers are calculated.