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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)

 

Updated 8 April 2012
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