Tony Raven said:Brian G <[email hidden]> wrote in
news:[email hidden]:
Quoted message said:Spurred on by discussion on urc and elsewhere, I've built a 700c front
wheel, from parts via Ebay (except for the spokes). I mostly followed
Sheldon Brown's excellent instructions and got on quite well with it.
It's a standard 32 spoke, 3-cross setup. I've set the tension mainly
by instinct and by comparison with other front wheels. I
stress-relieved it using all the methods I found reference to. I've
put it one of my bikes and run it for just over 150 miles, mainly on
smooth road but with some bumpy bits thrown in to test it a bit. It
runs pretty well true in both dimensions, although I had to do some
fine side to side tuning after about 50 miles.
So the question is, is that it? Is 150 miles enough of a road test
for me to say with confidence that the wheel will do, or is there
something else I need to look out for, beyond the normal checks and
maintenance?
If you compared the spoke tone with existing wheels you probably don't
have enough tension on them which is why you needed to fine tune after
50 miles. The tension should be set by either getting to the point
where the nipples are becoming too hard to turn without risking damaging
them or the wheel goes pringle shaped when stress relieved.
That may well be too much tension for a modern aluminium rim and result
in premature cracking around the spoke holes.
This has been flamed to death on RBT but even Jobst effectively agrees
with the conclusion as far as I can tell. He phrases it as "don't use
[censored] rims then" (he has stockpiled MA-2s himself from back in the day)
rather than as "don't use so much tension" but the facts themselves seem
to be in less dispute.
The idea of going to the pringle point and back a bit comes from Jobst's
book. As far as I know that is the origin of the meme, but I couldn't
say for sure.
I agree fine-tuning after 50 miles shouldn't be necessary. But I'm not
sure the taco/pringle/potato chip and back a bit principle is still such
a good idea unless you follow all of Jobst's advice and also use MA-2s.
Now a few people may say well I use lots of tension and my rims never
crack, and I don't disbelieve them, but things fail when the sum total
of contributory factors exceeds some limit, so it isn't easy to draw
conclusions from anecdotal evidence like that.
As for the question of how many miles before you declare a wheel well
and truly built, based on this,
http://hea-www.harvard.edu/~fine/opinions/frame-test.html, which is
actually about frames, I suppose that if you've gone for 280 hours (or
about 6000 miles) with no spokes breaking then you can assume they are
operating below their fatigue limit and therefore will last forever.