Originally Posted by
karungguni
Am a sub Clydesdale, 6'1, 195lbs, but friends say I ride like one. Average 800 miles, 60K feet of climbing a month. 2012 Specialized Tarmac Pro 58cm. Went through several sets of wheels. Previously split the rim on Ksyrium ESs. A friend gave me a pair of Mavic Open Pro 32 spoke, DT Swiss Spokes, Campy Record hubs tied and soldered running with 25mm tires 110 PSI in the back. They were built by a well known local wheel builder. Am having trouble keeping the rear wheel true.
One of several things is going on.
1. The rim is bent and can't be made true with sufficiently high tension in one or more spokes. With beam stiffness proportional to the cube of thickness shallow rims like the 19mm Open Pro are a lot less tolerant of hits than 25-30mm rims (the later could be 4X as stiff).
2. Your wheel builder sucks and didn't put enough tension in the wheel and the loose non-drive side spokes' nipples unscrew when they unload.
3. Your wheel builder sucks and didn't make the non-drive side tension sufficiently uniform so the looser non-drive side spokes' nipples unscrew when they unload.
4. Your wheel builder neglected to address windup, perhaps which was exacerbated by neglecting to lubricate the spoke threads.
A wheel built with straight gauge spokes would amplify the impact of tension problems because a small rim deflection makes a bigger change in spoke tension than butted spokes; and 2.0/1.5mm DT Revolution or Sapim Lasers in the non-drive side make for a more tolerant wheel.
Campagnolo hubs exacerbate the problem due to flange spacing which results in lower non-drive side tension at a given drive side tension (the wider freehub dictates flatter drive-side spokes on a centered rim, and Campagnolo brand hubs just happened to be spaced that way).
Off-center rims make things better.
That said, I've been riding a set of Chorus hubs since 1996 (upgraded to 9 cogs around 2000) without issue. DT 2.0/1.5 Revolutions except 2.0/1.8 champions rear drive side. Mostly the original DT alloy nipples. Open Pro rims (originally the lighter Reflex clincher, although it didn't take long to flatten the rear and I might have gotten months out of the front after breaking my leg and growing my belly to a 215 pound all-time high).
Is it the nature of the beast for larger guys
No.
Ridden with 2 180 lb. guys who are having problems with Zip 101s and 404s as well. Any words of wisdom?
Learn a little about wheel building and fix the problem. Building from scratch and fixing other peoples' screw ups is time consuming but not difficult, about as hard as adjusting a front derailleur.
You have two goals:
1. A true wheel (radial and lateral)
2. Sufficiently high tension in all spokes so the nipples don't unscrew and it takes a bigger hit to remove all tension at which point the rim is laterally unsupported, can move off center, and can taco when it springs back.
where
1. Even tension within a wheel side means no spokes appreciably looser than others (rims can leave the factory a little egg-shaped, the ferrule at the joint can make the rim stiffer, etc. so it won't be perfect) which will drop below the required tension.
2. You can fudge a bit on radial run-out without noticing (the tire's compliance will hide it) to favor lateral run-out for brake clearance and uniform tension.
When you true a wheel you choose the option of making it straight which tends towards more uniform tension in a side. If you have a bend opposite a loose spoke between tight neighbors you tighten that spoke and perhaps loosen its neighbors. If things are fairly uniform you spread changes out among neighboring spokes. Etc.
Add a drop of oil to each nipple and socket if you didn't think to use anti-seize or grease when building the wheel.
If you can't make it true with relatively uniform tension within a side the rim is bent. You can remove tension and unbend it or just replace the rim.
For deep section rims you want to measure absolute tension via a tension meter (Park's is affordable for around $50) or cell phone app which calculates based on pitch and unsupported span.
With shallow rims like the Open Pro and enough spokes like 32 you can use Jobst Brandt's method alternately adding tension and stress relieving (squeeze near parallel spokes in a side towards each other) until the wheel goes out of true in waves indicating you've reached the rim's elastic limit 'at which point you back off tension 1/2 turn and true. That'll get you to the same point - the last Open Pro rear I built that way averaged 105kgf on the drive side with a tire installed on the rim. Tighten the non-drive side as needed to center the rim (1/4 turn non-drive side for every 1/2 or 3/4 turns on the drive side will keep you close).
That doesn't work for deeper rims and low spoke counts because you'll get enough tension to risk stress cracks in the spoke bed before you reach its elastic limit.
I like to put a tape flag on the drive side and non-drive side spokes following the valve stem hole to see how much windup I'm getting so I can compensate. Other people like a Sharpie marker dot on each spoke.
Putting the axle end down on a piece of scrap wood and pushing down on the rim at 3 and 9 o'clock all the way around will help undo wind-up if you don't get that right.