AP said:(Previously 28 24 22 20 18 - sensible? doable? costly?)
I'm almost persuaded to cold set my frame, in order to accommodate a
7 speed block at the back, but I seem to remember reading somehwre
that to do this I'll need to redish the wheel. From what I've
googled, this sounds fairly daunting...a good way for a fool to
destroy a perfectly good wheel. I have used a spoke key, but rarely,
and only to tighten up loose spokes. Is redishing the kind of thing a
relative newbie can do?
If you can true a wheel, you can redish a wheel.
It's just a question adjusting the relative spoke tightness of one side,
checking, and adjusting again until it's acceptable.
If you reckon spoke tension is about right in the first place (not regarding
dishing, just generally), tighten the side the rim needs to go towards by
one whole turn each spoke, and loosen the other by half a turn each spoke.
Check the centering and repeat as necessary, using your judgement as to how
much of a turn, or many turns, is needed again. Carry on repeating or
correcting until done.
Some truing will be required as well (during or afterwards) because you
won't make /precisely/ the same difference to each spoke on each side, or if
there is some spoke wind-up. If it starts to go pear-shaped (metaphorically
or literally!), don't panic, it can be corrected. Still don't panic if your
attempted correction makes it worse. You (or a bike shop) will get it right
eventually.
If you think all the spokes are already slacker than ideal before you start
(this is common) then leave one side alone and just tighten the other. Vice
versa if the reverse is true - but this is rare. Have a feel of a similar
wheel if in much doubt.
You can use the bike frame to check the wheel is dished correctly by eye if
you don't have a dishing gauge. The rim should be centred between the
stays. Spin the wheel in case it isn't true and judge by the average. True
the wheel first if it's /too/ "buckled" to check the dishing.
Also check with the wheel fitted back-to-front to double-check and eliminate
other things. Don't judge the centering by the brake blocks as they may be
off-centre. However, you can use the blocks for truing as long as you're
aware of what's what.
To try and prevent wind-up (the spokes twisting), with whatever adjustment
you make to each spoke, either way, every time, turn the nipple about an
1/8th to a 1/4 turn too far, then back again to where you want it.
Hope that de-dauntifies it a bit for you instead of the opposite :-)
Proper professional instructions:
http://www.sheldonbrown.com/wheelbuild.html
~PB