What is 275/60R20 in imperial sizing?
Answer
33x12.50R20
275/60R20 measures 32.99 in tall and 10.83 in wide, so in imperial notation it is a 32.99x10.83R20. The nearest size genuinely sold on that wheel is 33x12.50R20, +0.01 in different.
The working
- 33x12.50R20
- 33.00 in tall, +0.01 in
- 35x12.50R20
- 35.00 in tall, +2.01 in
- 37x12.50R20
- 37.00 in tall, +4.01 in
- 38x13.50R20
- 38.00 in tall, +5.01 in
A perfect height match and no width match at all
The nearest flotation size is 33x12.50R20, and on diameter it is astonishingly close: 33.00 in against 32.99 in, a hundredth of an inch. Width is a different story. 12.50 in against 10.83 in is 1.67 in of difference, and unlike the height there is no alternative to choose instead.
The 20-inch flotation catalogue is one width wide
Look at what is actually produced on a 20-inch rim in imperial notation and the pattern is stark: 33x12.50R20, 35x12.50R20, 37x12.50R20, 38x13.50R20. Every one is 12.50 in or wider. The narrow flotation sizes — the 10.50s and 11.50s that exist on 15, 16 and 17-inch wheels — were never carried up to 20-inch fitments, because the vehicles running 20s were not the vehicles buying narrow flotation tires.
So a 275/60R20 has no imperial equivalent in any useful sense. It has an imperial size that matches its height and nothing that matches its shape.
The whole ladder is offset by a hundredth
Because this tire is 32.99 in, every flotation size above it clears by a value ending in .01: 33x12.50R20 is +0.01, 35x12.50R20 is +2.01, 37x12.50R20 is +4.01, 38x13.50R20 is +5.01. It is a small curiosity and a useful one — the steps between imperial sizes on this wheel are whole inches, measured from a metric size that happens to sit one hundredth below a round number.
What the substitution actually costs
Height is free: 0.02% of speedometer difference, which is to say none at all. Sidewall is free too — both tires carry 6.50 in, because a 33.00 in flotation size and a 32.99 in metric one on the same 20-inch rim have the same space left over to fill. Every meaningful difference between them is the 1.67 in of section width, which is unusually tidy for a cross-notation comparison and unusually unhelpful, since width is the one thing you cannot adjust by picking a different size here.
The exact conversion
32.99x10.83R20. Unmakeable, since flotation notation quantises diameter to the inch and width to the half inch, but it is the figure every rounded answer above is rounded from. Load the converter for the ranked list.