255/45R18 tires
Vehicles that use 255/45R18 as an OEM tire size, the tire models we currently catalog in this size, and the compatible alternative sizes within the ETRTO ±3% safe-fit tolerance.
255/45R18 dimensions
255/45R18 tires have a diameter of 27.0", a section width of 10.0", and a wheel diameter of 18". The circumference is 84.9" and they have 746 revolutions per mile. Generally they are approved to be mounted on 8-9.5" wide wheels. Specs may vary by manufacturer. learn more
Vehicles that use this size
Tires available in this size
Compatible alternative sizes within ±3%
Other tire sizes that fall inside the ETRTO safe-fit tolerance for 255/45R18. Sorted by smallest overall-diameter change.
| Alternative | %Δ OD | Sidewall Δ | Category |
|---|---|---|---|
255/50R17 |
0.01% | +12.8 mm | alternative |
255/40R19 |
-0.01% | -12.8 mm | plus 1 |
255/55R16 |
0.03% | +25.5 mm | alternative |
255/35R20 |
-0.03% | -25.5 mm | plus 2 |
225/40R20 |
0.19% | -24.8 mm | plus 2 |
285/40R18 |
-0.22% | -0.8 mm | wider |
285/45R17 |
0.23% | +13.5 mm | alternative |
225/45R19 |
-0.23% | -13.5 mm | plus 1 |
For the full categorised list (Plus-1, Plus-2, winter narrower, wider, etc.) with verdicts and speedometer impact, see 255/45R18 upsize options.
What changes if you go up or down one aspect step
The cleanest single-step swap is moving the aspect ratio by ±5 points on the same rim. The table below shows the math for 255/45R18 vs the adjacent ±5 aspect sizes.
| OEM 255/45R18 | Down to 255/40R18 | Up to 255/50R18 | |
|---|---|---|---|
| Overall diameter | 686.7 mm | 661.2 mm | 712.2 mm |
| % Δ vs OEM | — | -3.71% | 3.71% |
| Sidewall height | 114.8 mm | 102.0 mm (-12.8) | 127.5 mm (+12.8) |
| True mph at 60 indicated | 60.00 mph | 57.77 mph | 62.23 mph |
| Verdict (±3% rule) | — | Outside ±3% | Outside ±3% |
Shorter sidewall (down a step): sharper steering, harsher ride, higher pothole risk. Taller sidewall (up a step): softer ride, fuel-economy gain on highway, less precise handling. Use the compatibility calculator to evaluate any size pair beyond the single-step swap.
What 255/45R18 means
The first number — 255 — is the tire's section width in millimeters (about 10 inches from sidewall to sidewall, measured when the tire is mounted and inflated to standard pressure). The second number — 45 — is the aspect ratio: the sidewall height as a percentage of the section width, which works out to 114.8 mm of sidewall for this size. The R indicates radial construction (universal on passenger tires today, mandatory under FMVSS 109), and 18 is the rim diameter in inches. Together these give an overall tire diameter of 686.7 mm (27 inches) — the dimension that matters for speedometer accuracy, wheel-well clearance, and TPMS / ABS / AWD calibration.
100 vehicle/year combinations in our catalog list this size as an OEM or approved fitment, and 80 tire models in our catalog are sold in this size. Each one turns about 746 revolutions per mile (circumference 2157 mm × π), which is the figure your speedometer and TPMS modules are calibrated against. When you replace tires within the same size, brand and compound choice are what change the driving experience — every tire in this size is engineered to the same outside diameter, so speedometer error and wheel clearance won't change. Where the differences show up is in tread compound (longer-wearing vs stickier), construction (touring sidewall vs performance-stiff), and season class. For a deeper breakdown of what each digit in the size string represents, see the paired 255/45R18 explained page.
If you are considering deviating from 255/45R18 — a plus-size step up, a winter step down, or a same-rim width change — keep the overall outside diameter within ±3% of the original per the ETRTO 2024 §2.3 safe-fit standard. Major changes to outside diameter affect speedometer calibration (SAE J1349 ±4% factory tolerance), ABS rotational reference (FMVSS 135), TPMS rev/mile tracking (FMVSS 138), and AWD viscous coupling temperature on systems that rely on consistent tire revolutions per mile. The Compatible alternative sizes table above lists every size within tolerance, and the 255/45R18 upsize and downsize options page groups them by upgrade intent (Plus-1, Plus-2, winter narrower, wider, etc.) with verdicts and speedometer impact. Always confirm any non-OEM substitution with the manufacturer or a qualified tire shop before purchase.
For shoppers looking at this size, the key spec questions to ask are: does the tire's load index equal or exceed the OEM placard requirement (Tire & Rim Association 2025 Table 1-2 maps the number to maximum weight), does its speed rating match or exceed the placard, and what is its UTQG treadwear rating? The third question is the best single proxy for tread life: 600+ UTQG signals a long-wear touring compound, 400–600 is mid-life performance, under 300 is short-life high-grip. Cross-reference any candidate tire's spec sheet against the manufacturer's published technical bulletin before committing.
Last verified 2026-06-09.