Spokes breaking on rear wheel - too much weight?

[johnfitzgerald]

We're 1200km into our tandem ride to Istanbul.

All is not well at the back of the bike, however... we've been breaking a few spokes recently - three in one go about a week ago, and one yesterday. They've been breaking up at the threaded end.

I'm wondering/worrying that we might be carrying too much on the back rack? We have two very full Ortlieb 40l bags, plus a 4kg tent, plus two sleeping bags in a separate drybag (say another 3kg or so). So I'm guessing around 40kg for the luggage, and Rachel, who is stoking, is a fairly featherweight 70-75kg.

At the moment we're trying to find places in Zurich that stock extra 236mm spokes, without much luck.

Perhaps our back load is too much for the wheel? Also, is it likely that we need a rebuild on the wheel? We had a good mechanic check it in Basel after our first three spokes went, and he thought it was OK.

Thanks for your help!

www.fitzgeraldfreewheel.wordpress.com

[johnfitzgerald]

Perhaps I'm the first to encounter this problem?

Anyway, a mechanic here in Switzerland (and wise heads back in the UK) has pointed out that we have probably had one of a bad batch of rims, where the spokes go in at a bad angle, because the holes are drilled at the wrong angle. It turns out that a Rohloff hub needs straight spokes, otherwise they receive too much strain and snap. Lucky for us that our bad rim played up while we were near some clever mechanics...