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Tire sizes

285/75R18 — the closest a metric code gets to a real 35

Seventeen hundredths of an inch, and the reason nobody calls this size a 35.

Metric notation · Light truck (LT-metric)

Overall diameter
34.83 in
885 mm
Section width
11.22 in
285 mm
Sidewall height
8.42 in
214 mm
Aspect ratio
75%
sidewall as a share of width
Wheel diameter
18 in
the hole in the middle
Circumference
109.4 in
2779 mm
Revolutions per mile
579.0
geometric, not measured
Revolutions per km
359.8
geometric, not measured
Typical load index
108–129
2205–4079 lb per tire

LT-metric tires use a stiffer casing at a much higher reference inflation — Load Range C, D or E, meaning 50, 65 or 80 psi. The index band reflects the pressure the casing is rated to hold, not a larger tire.

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

  • 35x12.50R1835.00 in tall+0.17 in
  • 33x12.50R1833.00 in tall-1.83 in
  • 37x12.50R1837.00 in tall+2.17 in

Compare any two sizes, including ones this site has no page for, in the comparison tool.

Platforms recorded with this size

The second-generation Toyota Tundra lists 285/75R18 as a common upgrade. It is the only vehicle record here that mentions it.

Nearer than anything else metric

Five flotation codes in this catalogue compute to 35.00 in — on 15, 16, 17, 18 and 20-inch wheels. The metric sizes that come closest to joining them are:

  • 285/75R18 — 34.83 in, 0.17 in short
  • 295/65R20 — 35.10 in, 0.10 in over
  • 285/65R20 — 34.59 in, 0.41 in short
  • 315/70R17 — 34.36 in, 0.64 in short

Only two metric codes here land inside a quarter of an inch of a 35, and this is one of them. On its own wheel it is closer still to the flotation size it shares that wheel with: 35x12.50R18 is 0.17 in taller and 1.28 in wider, a difference of 0.49% in height and rather more than that in appearance.

Deep casing on a large wheel

8.42 in of sidewall is a great deal for an 18-inch fitment, and it is what a 75-series aspect ratio produces once it is applied to a 285 mm section. The same figure appears on 285/75R16, which uses the identical width and aspect on two inches less wheel and therefore stands 2.00 in shorter at 32.83 in.

Those two are the deepest-cased 285s in the catalogue, and both of them are upgrades rather than factory fitments — a reminder that the sizes with the most casing depth are increasingly the ones somebody has to go and buy deliberately.

What the step costs from below

Coming from Diameter Step Actual speed at an indicated 70 mph
275/65R18 32.07 in +2.76 in (8.59%) 76.0 mph
285/65R18 32.59 in +2.24 in (6.89%) 74.8 mph
33x12.50R18 33.00 in +1.83 in (5.55%) 73.9 mph
275/70R18 33.16 in +1.67 in (5.05%) 73.5 mph
285/70R18 33.71 in +1.12 in (3.33%) 72.3 mph

Each percentage in that table is measured against the tire being left, not against this one, which is the only way a "coming from" figure means anything. Read the other way round the same 2.76 in step from 275/65R18 would be quoted as 7.91%, and both numbers would be correct about different questions.

Coming from the Tundra's own 275/65R18, then, this is an 8.59% change: a hundred indicated miles becomes 108.6 real ones. The speedometer calibration reference sets out how that single ratio propagates through every distance and speed reading the vehicle produces.

Related

Class: Light truck (LT-metric). Every figure above is computed from the size code, not stored — see how these numbers are calculated.