Sorry my friends, I have a doubt regarding the tyres of a Triumph NSD 550cc 1928....seems to be 26x3,25. Does it means R19x3.25 or R21x3.25? Does anyone has the tecnichal data of that nice bike? Thanks Devis.

email (option): vadori@libero.it

Devis, yet more British weirdness for you I'm afraid. Motorcycle tyres in the 1920's were of the "Beaded Edge" type and were measured by their outside diameter (in inches, naturally). Later tyres were of the "Wired" type and were measured by inside (wheel rim) diameter. I suspect that a 21" wired tyre is about the same size as a 26" beaded edge tyre, BUT you cannot interchange them as they fit into the wheel rim in very different ways and using very different rims. And beaded edge tyres need pumping up to much higher pressures.

You may have to buy your 26" tyres (if you are sure that is what your bike uses) from vintagetyres.com or vmcc.net. They will be able to advise you better than me.

Chris J

P.S. Have you shared the joke about Tesco nuts with your friends yet?

The dual use of tyre size outside diameter and rim size continued with wired on tyres into the 1940s.

The Norton WD16h maintenance manual quotes:

Wheel Rim Size 19xWM2

Tyre Size 26" x 3.25"

A 19 x 3.25 tyre with a 100% aspect ratio (ie 3.25" high) adds a total of 7" to the outside diameter of the 19" rim = 26"

Apparently everybody understood at the time.

Dear friends thanks a lot for the info. So I will use R19 :-) The problem is the front brake...is lost, and I have to find one. Regarding my "Tesco experience" all my friends understand the situation - "if the girl was nice...." have a nice day, Devis V.

email (option): vadori@libero.it