Bicycle wheel sizing
Please feel free to call for advice on the correct sizing of your vintage bicycle wheels and rims if you are in any doubt. Bicycle wheel sizing can be confusing particularly as it is done on a different principle to that of cars or motorcycles. The main diameter (for example 26 inch) does not refer to the physical diameter measurement of your wheel rim. Bicycle wheels are measured by the tread-to-tread diameter of the tyre. The second measurement (for example 1-3/8” or 1-½”) refers to the nominal profile of the tyre. Therefore, both 26 x 1-½” and 26 x 1-3/8” tyres would both measure 26 inches tread-to-tread but, as 1-½” is a larger (deeper) profile than 1-3/8” the rim for that wheel would actually be smaller in diameter. Fractional marking such as 28” x 1-5/8 x 1-3/8 (approximate outer diameter x tire height x tire width) is also common. The true measurement of the rim is cross referenced using the sizes determined by ERTRO ~ European Tyre and Rim Technical Organisation (See their website http://www.etrto.org ) The rim measurement is taken from the bead seat diameter (where the tyre bead sits onto the inside of the rim) in millimetres which is hard to measure accurately with a tape measure. Therefore, a 26 x 1-½” rim is 584 mm whereas a 26 x 1-3/8” rim is 590 mm. This explains why many people find it impossible to fit seemingly similar tyres to their rims. In most cases however, the wheels fitted with their correct size tyres are interchangeable as complete units so a 26 x 1-½ wheel and tyre will successfully replace a 26 x 1-3/8” wheel and tyre. I should also mention that metric and Imperial/fractional sizes also differ from each other. A 26 x 1.75 sized rim and tyre (ETRTO 559 mm) is very different in size to a 26 x 1-3/4” rim and tyre (ETRTO 571 mm)
Vintage bicycle wheel rims
Generally there are two main rim types. West wood style applies mainly to rod brakes where there is no sidewall to the rim as the braking surface is on the flat face of the rim next to the spokes as the brake blocks pull upwards onto the rim. Westwood rims are also used where coaster (back pedal) brakes are used and also where drum brakes are used.Rim brakes such as caliper brake use Endrick style rims which feature side walls for the caliper blocks to face onto. Raleigh Bicycle Company developed a variation that combined the rod braking surfaces of Westwood rims with flat sides for caliper braking. It has been called "Raleigh Pattern" and "Westrick". They are noted for their strength and have also been copied by Schwinn in North America.