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Tire sizes

285/35R20 — the top of a very short ladder

The last performance size before a 20-inch wheel becomes a truck wheel.

Metric notation · Performance and ultra-high performance

Overall diameter
27.85 in
708 mm
Section width
11.22 in
285 mm
Sidewall height
3.93 in
100 mm
Aspect ratio
35%
sidewall as a share of width
Wheel diameter
20 in
the hole in the middle
Circumference
87.5 in
2223 mm
Revolutions per mile
724.1
geometric, not measured
Revolutions per km
449.9
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

  • 33x12.50R2033.00 in tall+5.15 in
  • 35x12.50R2035.00 in tall+7.15 in
  • 37x12.50R2037.00 in tall+9.15 in

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

No vehicle record on this site ships 285/35R20 or lists it as an upgrade, which puts it firmly in aftermarket territory: wide rear fitments on rear-drive cars, and replacement sizing for factory-fitted 20-inch wheels.

The ceiling of a very short range

Five codes make up everything a 20-inch wheel offers a car in this catalogue, and they occupy 1.10 in of overall diameter between them — barely more than one aspect-ratio step on a truck size. This size is the tallest of the five, at 27.85 in, and it is also the deepest-cased at 3.93 in.

Above it the wheel changes purpose entirely. The next catalogued 20-inch tire is 245/50R20 at 29.65 in: 1.79 in and 6.43% taller, on a casing 1.57 in narrower, and built for a crossover.

Deepest casing without being the widest

3.93 in of sidewall is more than any other performance size on this wheel carries, and it comes from being the widest 35-series code rather than from any change of shape — the percentage is applied to 285 mm rather than to 245 or 255.

One size on the wheel is wider still. 305/30R20 measures 12.01 in across, 0.79 in more than this tire, and it manages only 3.60 in of casing because its middle number is five points lower. So the widest tire on the wheel is not the deepest, and this one holds that distinction while sitting second on width.

Fitted behind something narrower

As a rear size the practical question is what stands at the same height on the front axle. 275/35R20 is 0.28 in shorter, which is 0.99% — the closest match available, and small enough that a front-to-rear diameter difference of that order is inside ordinary manufacturing variation.

255/35R20 and 245/35R20 are 0.83 in and 1.10 in shorter. Those are real mismatches rather than rounding, and what a permanent difference in rolling diameter between axles implies for a differential or a four-wheel-drive system belongs to the pair rather than to either size. The staggered fitments reference treats it.

Related

Class: Performance and ultra-high performance. Every figure above is computed from the size code, not stored — see how these numbers are calculated.