When replacing spokes on the rear wheel of my road bike using a tension meter what should the max tension be? I had a spoke snap whilst riding a couple of days ago and it became lodged in the cassette locking my back wheel which caused it to buckle. I will true it up using the spokes but am unsure about max tension and then whether to back off the tension to ride again.
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2If the rest of the spokes are still equally tensioned, just tension the new spoke to the same tension. However, usually spokes don't break while your spokes are equally tensioned, so you won't have one observed tension to go by. You'll most likely need to redo the entire spoke-tensioning / wheel-truing process. Equal spoke tension is much more important to wheel stability than absolute tension.– cmaster - reinstate monicaMar 14, 2019 at 8:14
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2 Answers
There is no hard-and-fast rule for max spoke tension. (Other than "Dang, there's a crack in the rim at this spoke hole." That means you added too much tension...)
In my limited wheelbuilding experience, I've found that the non-drive side spoke tension on 10- or 11-speed rear wheels pretty much sets the tension of the drive-side spokes.
First, all of the spokes need to have sufficient tension to prevent them from ever becoming unloaded. Spokes that become completely unloaded (no tension at all on the spoke) will fail rapidly. The exact force to ensure that no spokes ever become completely unloaded is going to depend on the usage, the wheel geometry, and probably the phase of the moon. I'd say anything above 50 kgf will probably suffice.
Second, spoke tension mustn't be so high that you risk catastrophic failure from transient loads like hitting a bump. You don't want your wheel tacoing out from under you during a fast descent just because you hit a misaligned pavement joint. Spokes at high tensions risk such failures because the high tension can put wheel components close to the point of permanent deformation (cracking, bending or, in the case of spokes, stretching permanently). Again, exact values depend on the components, geometry, and a lot of other factors. But I'd venture anything greater than 120-140 kgf is too much.
In my experience, when truing up a new 10- or 11-speed rear wheel, once the non-drive side tension is greater than 50-60 kgf, drive-side tensions start getting up over 100 kgf.
In other words, once you get enough tension on the non-drive side spokes to prevent them from unloading, drive-side spokes are getting up close to maximum safe tension.
DT Swiss has a blog entry/sales pitch at https://www.blog.dtswiss.com/spoke-tension/ that I think is worth reading.
answered Mar 14, 2019 at 10:14
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Regarding breaking spokes by transient loads, have you ever read how load is spread on a tensioned spoke wheel?– ojsMar 14, 2019 at 13:49
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@ojs Regarding breaking spokes by transient loads Where do I say anything about "breaking spokes by transient loads"? I posted "Spokes at high tensions risk such failures because the high tension can put wheel components close to the point of permanent deformation (cracking, bending or, in the case of spokes, stretching permanently)" Mar 14, 2019 at 14:01
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1Oops, you are correct that you did not mention breaking spokes in that context. So, how does transient load increase spoke tension enough to cause permanent stretching?– ojsMar 14, 2019 at 14:23
For asymmetric wheels (most rear wheels which don't use a single speed or internal gear hub) you’ll usually try to use the maximum allowed tension on the drive side. The limit is set by the rim manufacturer, most allow around 1200N of tension.
The non-drive side requires much less tension to pull the rim towards the center (“to dish it”). Low spoke tension is bad because bumps in the road can unload the spokes completely which can allow them to move slightly (causing abrasion/wear) or even unscrew.
Therefore you’ll want to use the maximum tension on the drive side to be able to use sufficient tension on the non-drive side. With 1200N on the drive side you’ll reach about 600N on the non-drive side.
Use a high-quality spoke wrench and grease or lube on the drive side spoke nipples.
