Quoted message said:Do I need to worry about the variability in spoke tension?
First of all, it's important to know that the left and right side
spokes of rear wheels for derailer bikes, and on several other types of
rear wheel, use different tensions. There's more tension on the drive
side spokes, which isn't a good thing but is inherit to any wheel where
the spoke-end centerline is going to end up anywhere but exactly
between the two flanges. It's unclear whether you know this or not.
The rest of the conversation actually gets pretty complex, especially
when you get into whether the shop did a good/honest job or not. I can
tell you now that whether they did or not, they did a common one for
the situation.
Tension balance among all spokes on each side of a wheel is
important/beneficial for a few reasons. Large disparities in tension
make wheels susceptible to become damaged prematurely at best and fail
at worst. Most wheels out there on dealer-level bikes are built good
enough that these aren't issues, but aren't as well tension balanced as
they could be by a long shot (and the argument exists and is pretty
good that 8/9/10 speed wheels are all damage prone and unsafe for
basically the same reaons that a shoddily tension-balanced wheel is).
Truly precise tension balance, beyond the "pretty reasonable" norm,
gets you an additional level of long-term durability that occurs for
different physical reasons than the ones that make wheels with slack
spokes die early. Some wheels aren't capable of this for reasons having
to do with the construction method and precision of the rim.
In general, the way that a conventional spoked bike wheel supports
weight is by the built-in tension loads on each spoke taking turns
temporarily absorbing the compressive loads the wheel encounters as you
mount the bike, ride along, hit stuff, etc. At any one time on a 32 or
36 spoke 26" or 700 wheel, the load on the wheel is shared by about 4
spokes. That number changes for wheels of different sizes and spoke
counts. Anytime that a wheel is loaded so much that any of the spokes
lose all their tension (go slack), it's possible for the wheel to
become damaged, or fail in some (usually but not always extreme) cases.
Clearly, this indicates that it's not good to have spokes that are
slack or near-slack before you even get on the bike. If the tension
imbalance in your wheel is extreme enough, which sounds possible, the
wheel could fail or become damaged as a result. It most likely was
already damaged from being ridden in the conditions you describe with
loose spokes, and those spokes probably became loose because the wheel
was always undertensioned or poorly tension balanced.
The type of damage that occurs most often is that the rim becomes
deformed. Once this has occurred, and it usually already has by the
time someone gets into the type of situation you're describing (big
rider, big bumps, bike that actually gets ridden, noticeable spoke
tension issues after a shop has already laid hands on it), it's
impossible to make the wheel both true and tension balanced at the same
time. If you understand the basics of how wheel truing works -tighten a
spoke and the rim moves in that spoke's direction-, you can probably
understand why. The only way a wheel can be both as perfectly true and
perfectly tension balanced as bike wheels get is if the rim is
perfectly straight and round before it has any spoke tension acting on
it. (And no wheel can be absolutely perfect in this regard, because
rims are all stiffer at the seam and so they respond to tension
differently there, making either tension disparities or radial truth
disparities inevitable).
It's also common for loose spokes to allow the nipple to move when
ridden, making the spokes looser and perpetuating both the
nipple-loosening and the rim-damaging problem.
That the left spokes have tension differences that are easy to feel by
hand isn't good, but how bad it is depends on how large the differences
are and whether any spokes are completely slack, or close to it. 8/9/10
speed wheels usually have very loose left spokes, which sucks and makes
these wheels inherently less durable (because even though the wheel has
the very-tight right spokes to support it, the left ones still are
forced to operate at very low or, in practice with many typical
mass-produced wheels, basically no tension. This is especially true of
wheels with light rims. That mass-produced wheels are usually built way
under-tension and with poor tension balance anyway makes the problem a
lot worse).
It's easier to feel differences in tension between lower-tension spokes
by hand than it is with higher-tensioned ones. Among the less-tensioned
spokes, smaller variances in tension also result in easier to feel
differences than they do on spokes in a higher tension range. So based
on your description, it is possible that things are basically okay, and
that the left-side spokes are all in the reasonable-but-not-stellar
range, and that you managed to avoid significantly damaging the wheel
when you were riding it with loose spokes before. However, it's not
likely at all. What's probably going on is that the rim is now messed
up and whoever trued the wheel compensated for that by letting spoke
tensions be uneven, probably in the right side spokes as well, and also
probably didn't do anything to correct a too-low-to-begin-with tension
level, which most wheels that are having problems but aren't being
abused are suffering from. And they also probably didn't make the
tension balance on the wheel as good as it could be while still true,
either, which is hard to do on a messed up rim. And it's also likely
the wheel is laterally pretty true but far from as-good-as-it-gets
radially. This is all fairly standard practice for shops, and whether
it's particularly wrong or they should have told you or should have
pointed you to a new wheel or whatever is a complicated discussion, and
depends on how bad your wheel really is, which I can't tell from here.
Most shop mechanics deal with a *lot* of wheels having some form of
these problems. Mass-produced wheels that get ridden, especially by
heavier riders, are basically guaranteed to have them, unless they get
loved up before being ridden by someone who knows what they're doing
and is willing to spend more time on them than an average bike shop can
afford to spend on a wheel true at market rate.
However, if this is to the point where any spokes on the wheel are
completely slack, or obviously close to it, and the shop handed it to
you that way with no warning and told you to ride it, that's
irresponsible and wrong of them. Loose spokes do cause wheel failure in
practice, just not very often. Where to draw the line in practice of
how loose or imbalanced is too much is something that's basically
glossed over day-to-day in most shops.
And the reason I bother writing all this is because I'm also no
lightweight rider, and this [censored] needs to be more understood so that
heavy people can ride bikes.
