John B. wrote:

One of the "etc's" has to be "and how far do
you ride in a normal year, Sir?"

Wait, isn't that a function of the answer to
*my* question (how many bike hours does a chain
last) and the speed data?

Obviously the average speed of urban cycling
isn't 25 km/h. It is rather 15 or 10 km/h.
Let's say 15 km/h to make the experiment more
"fit"

So now the data is:

- A single speed bike, either Torpedo or
Shimano.

- It does have a chain guard.

- The chain is the Shimano CN-NX10 1S which
is 1/2*1/8.

- Speed doesn't exceed 25 km/h; average speed
is 15 km/h.

- The person cycling weights in at 80 kg.

- The chainwheel and sprocket are 10-15 years
old.

- The chain is lubricated one a month.

--
underground experts united
http://user.it.uu.se/~embe8573