On Thursday, January 10, 2019 at 7:04:10 PM UTC-8, Mark J. wrote:
Wheel building questions (including "religious" questions to replace the
political ones with which RBT has become saturated).

Background: I am re-rimming a wheel.
Hub: Powertap GS, 24 spoke (NOT disc)
Spokes: Sapim CX-ray bladed straight-pull
Old Rim: Velocity A23 O/C (offset) 700C non-eyeletted rim
New Rim: DT 411 (also offset), uses DT-supplied/mandated nipple washers.

Original build tension measured with a Park tensiometer, drive side
tensioned to Velocity's recommended max, even tension on each side.

Other: I'm ~170 lbs and strong enough though not as in days of yore, but
bike is geared quite low so on the steep stuff, the hub sees a fair bit
of torque. Tires 700x25, typically 105-110 psi. Paved road use except
for a handful of miles.

I built the original (Velocity) rim in 2015, had no problems until
recently (9900 miles later). Now I notice the rim starting to crack at
the spoke holes (only the pulling spokes on the drive side). Wheel was
still rideable and true when I unlaced it, so the cracks weren't severe yet.

NOTE: I KNOW (IMHO) that I'm pushing the margins with this build, so if
I can only get 10,000 miles and 3 years out of a wheel like this, I'm OK
with that, but I'll be happy to get more. I have plenty of more
durable/reliable wheels, but I've had fun with this wheel, and fun is
why we're here.

QUESTIONS:

Q1: I don't use thread compound or linseed oil, and would rather not
start now. I lubricate threads and nipple/washer contact with light
grease. What is a reasonable minimum non-drive-side tension to be
confident the spokes won't loosen?

I'm partway though tensioning the new rim, and think I can get the NDS
up to ~80 kgf if I push the DS up to DT's recommended max tension (1200
Newtons, or 122 kgf). I'm confident 80kgf is plenty on the NDS, but I
may want to put less than max tension on the DS (and thus less that 80
kgf on the NDS) to give me more margin on the cracking problem.

Q2: Do we suppose DT's (and/or Velocity's) max tension recommendation
has enough margin that stress-relieving the spokes won't overstress the
nipple holes? I reefed on the last build pretty hard at
stress-relieving time, Could that have weakened the rim in a way that
only showed up 10,000 miles later? I have belonged to the church of
stress-relieving for a long time, but my faith is weak.

Q3: (let the religious wars begin!) I would think that stress-relieving
is of primary benefit with J-bend spokes. Does it really help with
straight-pulls?

Notes: I have studied the sacred writings of the Jobst, on multiple
occasions, though I'll admit I'm having a hard time fully grokking his
stress-relieving argument.
I just did it 'cause "why not?" Now I'm quavering.
Also note that with bladed straight-pull spokes, any spoke wind-up would
be immediately obvious ('cause bladed), and anyway perhaps impossible
because the entire spoke, including the head, just turns on you.


Right now my inclination is to tension the DS at the recommended limit,
stress-relieve just a little less vigorously than last time, hope that
the nipple washers that DT mandates (and supplies) will spread out the
stress better at the nipple holes, expect at least 10k miles of
usefulness, and hope for more.

Thoughts? (esp. on questions Q1, Q2, and Q3 above)

Mark J.

Velocity recommends 110-130kgf whether or not that stays true. That's why I use linseed oil now. I've cracked spoke holes on Aeroheads at those tensions.

-- Jay Beattie.