Boxerworks.com

Thanks Kurt - 267.pdf provides the answer. It might also be the answer as to why I spin the back wheel in the wet and eat three and a half inch rear tires at the rate I do.

0,77:0,75 is 1.02666 and that's fleas in a gnat's knickers. Exactly the kind of change you want for a four inch tire.
+10km/h at 50 is 20%.

Sorry - I forgot to mention the actual numbers.
27/8 is 3.375:1.
25/8 (solo R60) is 3.13:1.
27/7 (s/c R60) is 3.86:1.
25/7 (R60US) is 3.57.

27/8 (what I have) seems to be standard a late type R69S.

I've been looking up the numbers since. Much becomes clear and some becomes muddy. I bought the bike 25 years ago when I lived in the Netherlands. According to it's papers, it was dutch from new. It's a very late bike by its numbers - amongst the last few made. Being dutch and the Netherlands being ...

I never knew there was a number on the outside of the final drive.

"27/8", it says. The speedometer number is "0,75".

I used a GPS speedometer/odometer on a recent run and got very different readings from my 1969 R60/2's own instrument. The bike is recording a significantly greater speed and distance covered than the GPS. It's out by enough for me to question which final drive is fitted. Speedometers on most vehicl...