Rim Diameter

The wheel size of cars has varied over the years as has the way they were measured. Starting with some very tall wheel rims in the early period of vintage cars, shrinking down as low as 10” for the classic Mini, and even 8” for some of the Micro cars of the ‘50s, and again today with the extremely low profile modern tyres we are back up to 21” wheels again. Here are some examples of different rim dimensions in the hope that it will help you recognise yours.

Rim Dimensions

• Vintage rim dimensions – The earliest pneumatic tyres were beaded edge tyres and the tyres designation displayed the overall diameter and the section height. So the rim dimension was calculated by doubling the section height and taking it off the overall diameter. eg 880X120 = 880mm – 120mm – 120mm = rim diameter 640mm (or 22”)
• Straight sided rim diameter – this is a wired on tyre technology used predominantly in the States. Using the same theory as the beaded edge vintage rim description, but in inches. Eg 33X5 = 33” overall diameter minus 5” at the bottom and 5” at the top = 23” rim diameter
• Cross ply rim diameter – the rim diameter is the number at the end of the tyre description 6.00X16 has a 16” rim and 450X19 has a 19” rim (however in the vintage period a tyre such as a 450X19 might have been called a 27X4.40. for any confusion with tyres like this please give us a ring +44 (0) 1302 711123)
• Classic Radial tyre rim dimensions – within a radial tyre dimension again it is the last number that is the rim diameter eg 185VR16 has a 16” rim or 345/35R15 has a 15” rim.
• Bibendum Rim Diameter – There have been a few periods where Michelin have attempted to move the world of tyres onto using metric sizes such as 13X45 tyres with a 45cm rim. These will generally have a well that goes only part way round the rim and a central valve. Then later 130/140X40 on a 40cm rim.
• Early millimetric radial rims – the first radial tyres were made to be fitted to 400mm wheels on cars like a Traction Avant & Lancia Aurelia with tyres like 165R400
• TRX tyre rim diameter – though these are quite special unusual tyres their description follows the same format as other radial tyres, where the rim diameter is the last number eg 190/55R340 (340mm rim) or 240/45R415 (415mm rim)

If you find this at all confusing please do Contact us and we will try to put your mind a rest.