TYRE SIZE CONVERSION - ETRTO / ISO TO OTHER COMMON TYRE
SIZE DESIGNATIONS
The ETRTO (European Tyre & Rim Technical Organisation) or ISO (International Standards Organization) designation now appears on almost every tyre and most inner tubes (or at least the packaging they are sold in). They can appear very confusing especially if the more familiar designations are not also on the tyre as is increasing common now. Adding to this confusion some the "familiar" designations actually relate to more than one rim diameter so, for example, the 20 x 1 3/8 tyre you purchase may not fit your 20 x 1 3/8 rim! Here the ETRTO / ISO designation helps avoid this problem and the added difficulty that tyre makers sometimes use slightly different nominal size designations to describe the same ETRTO / ISO designation. This is why some apparent inconsistencies appear in the chart below. The two digit number before the dash in the ETRTO / ISO designation describe the nominal internal width (section width) and the three digit number after the dash relates to the tyre bead diameter and the rim bead seat diameter, all in millimetres.
| ETRTO/ISO | COMMON SIZE DESIGNATION |
|
47-203 |
12 1/2 x 1.75 x 2 1/4 (also 12.5 x 1.75) |
|
54-203 |
12 1/2 x 2.10 |
|
57-203 |
12 1/2 x 2 1/4 |
|
62-203 |
12 1/2 x 2 1/4 x 1 1/2 (also 12 1/2 x 2 1/4) |
|
47-222 |
11 x 1 3/4 |
|
47-254 |
14 x 1.75 |
|
37-288 |
350A |
|
44-288 |
14 x 1 3/8 x 1 5/8 (350A) |
|
37-298 |
14 x 1 3/8 |
|
47-305 |
16 x 1.75 |
|
50-305 |
16 x 1.90 |
|
54-305 |
16 x 2.00 |
|
57-305 |
16 x 2.125 |
|
62-305 |
16 x 2.125 |
|
37-340 |
400A |
|
44-340 |
16 x 1 5/8 |
|
37-349 |
16 x 1 3/8 |
|
40-355 |
18 x 1.50 |
|
47-355 |
18 x 1.75 or (18 x 1.75 x 2) |
|
32-357 |
17 x 1 1/4 |
|
32-369 |
17 x 1 1/4 (Moulton) |
|
37-387 |
18 x 1 3/8 |
|
28-390 |
450 x 28A |
|
37-390 |
450A |
|
37-400 |
18 x 1 3/8 |
|
54-400 |
20 x 2 x 1 3/4 |
|
28-406 |
20 x 1 1/8 |
|
32-406 |
20 x 1.25 |
|
35-406 |
20 x 1.30 |
|
37-406 |
20 x 1 3/8 |
|
40-406 |
20 x 1 .50 |
|
47-406 |
20 x 1.75 or (20 x 1.75 x 2) |
|
50-406 |
20 x 1.90 |
|
54-406 |
20 x 2.10 |
|
57-406 |
20 x 2.125 |
|
37-438 |
20 x 1 3/8 |
|
28-440 |
500 x 28A |
|
37-440 |
500A
(also known as 20 x 1 3/8) |
|
37-451 |
20 x 1 3/8 |
|
47-457 |
22 x 1.75 |
|
37-490 |
550A (22 x 1 3/8) |
|
28-490 |
550 x 28A |
|
37-501 |
22 x 1 3/8 |
|
19-507 |
24 x 3/4 |
|
25-507 |
24 x 1.00 |
|
47-507 |
24 x 1.75 |
|
50-507 |
24 x 1.90 |
|
51-507 |
24 x 1.95 |
|
75-507 |
24 x 3.00 |
|
28-540 |
600 x 28A |
|
37-540 |
24 x 1 3/8 |
|
25-559 |
26 x 1.00 |
|
32-559 |
26 x 1.30 |
|
35-559 |
26 x 1.30 |
|
37-559 |
26 x 1.40 |
|
40-559 |
26 x 1.50 |
|
44-559 |
26 x 1.60 |
|
47-559 |
26 x 1.75 (or 26 x 1.75 x 2) (sometimes labelled 26 x 1.85 or 26 x 1.90) |
|
50-559 |
26 x 1.90 (sometimes labelled 26 x 1.95) |
|
51-559 |
26 x 1.95 |
|
54-559 |
26 x 2.10 (sometimes labelled 26 x 2.00 or 26 x 2.125) |
|
57-559 |
26 x 2.125 (sometime s labelled 26 x 2.10 or 26 x 2.25 or 26 x 2.30) |
|
60-559 |
26 x 2.35 |
|
62-559 |
26 x 2.50 |
|
75-559 |
26 x 3.00 |
|
19-571 |
26 x 3/4 |
|
20-571 |
650 x 20C (26 x 3/4) |
|
22-571 |
26 x 1.00 |
|
23-571 |
650 x 23C (26 x 1.00) |
|
47-571 |
26 x 1 3/4 |
|
32-584 |
26 x 1 1/2 |
|
35-584 |
26 x 1 1/2 |
|
37-584 |
26 x 1 1/2 x 1 3/8 (650 x 35B) |
|
40-584 |
26 x 1 1/2 (650B standard) |
|
28-590 |
650 x 28A |
|
35-590 |
26 x 1 3/8 (650 x 35A) or (26 x 1 x 1 3/8) |
|
37-590 |
26 x 1 3/8 |
|
40-590 |
650 x 38A |
|
42-590 |
650 x 40A |
|
32-597 |
26 x 1 1/4 |
|
37-609 |
27 x 1 3/8 x 1 1/2 |
|
18-622 |
700 x 18C |
|
19-622 |
700 x 19C |
|
20-622 |
700 x 20C |
|
22-622 |
700 x 22C |
|
23-622 |
700 x 23C |
|
25-622 |
700 x 25C |
|
28-622 |
700 x 28C (28 x 1 1/8) or (28 x 1 1/8 x 1 5/8) |
|
32-622 |
700 x 32C (28 x 1 1/4) or (28 x 1 1/4 x 1 5/8) |
|
34-622 |
700 x 34C |
|
35-622 |
700 x 35C (28 x 1 3/8 x 1 5/8) |
|
37-622 |
700 x 37C (28 x 1 3/8) or (28 x 1 3/8 x 1 5/8) (sometimes labelled 700 x 35C) |
|
38-622 |
700 x 38C |
|
40-622 |
700 x 40C (28 x 1.50) or (28 x 1 1/2 x 1 5/8) (sometimes labelled 700 x 38C) |
|
42-622 |
700 x 42C (28 x 1.60) (sometimes labelled 700 x 40C) |
|
47-622 |
700 x 47C (28 x 1.75) or (28 x 1 3/4 x 1 /4) (sometimes labelled 700 x 45C) |
|
50-622 |
700 x 50C (28 x 1.90) |
|
25-630 |
27 x 1 |
|
28-630 |
27 x 1 1/8 |
|
32-630 |
27 x 1 1/4 |
|
40-635 |
28 x 1 1/2 (700B Std.) |
|
37-642 |
28 x 1 3/8 (700A) |
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