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Spoke profile for a heavy duty wheel

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Spoke profile for a heavy duty wheel

Old 02-05-20, 02:13 AM
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csport
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Spoke profile for a heavy duty wheel

Hi

I know that similar questions are asked from time to time... I am rebuilding my rear wheel with a Velocity Chukker 700c rim and Shimano Deore M6000 rear hub with 36 spokes. I am 300#, and I may occasionally do light/medium duty touring on this wheel in addition to road/dirt trail riding.

I intend to follow Sheldon Brown's recommendation regarding different spoke thickness for the two sides of a dished wheel. Flange offset is 21mm/33mm for the right/left side. For the same relative elongation of the spokes on each side one would need the ratio of diameters equal to the square root of the tension ratio; i.e., sqrt(21/33) = 0.80.

I considered the following spoke (all Sapim) combinations:
  • Strong (2.3/2.0 single butted) DS, D-Light (2.0/1.65/2.0 double butted) NDS. This most closely follows the diameter ratio of 0.8.
  • Strong (2.3/2.0) DS, Force (2.18/1.8/2.0 triple butted) NDS. Force will be thicker and stronger near the hub.
  • Force (2.18/1.8/2.0) DS, D-Light (2.0/1.65/2.0 double butted) NDS. Both DS and NDS spokes are thinner in the middle, unlike previous configs.
  • Force (2.18/1.8/2.0) DS, Laser (2.0/1.5/2.0) NDS. Probably too thin on the NDS, but both sides are thinner in the middle and the thickness ratio is followed. May stretch too much under the load.
What would you recommend? Am I overthinking it?
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Old 02-05-20, 08:46 AM
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Originally Posted by csport View Post
Hi

I know that similar questions are asked from time to time... I am rebuilding my rear wheel with a Velocity Chukker 700c rim and Shimano Deore M6000 rear hub with 36 spokes. I am 300#, and I may occasionally do light/medium duty touring on this wheel in addition to road/dirt trail riding.

I intend to follow Sheldon Brown's recommendation regarding different spoke thickness for the two sides of a dished wheel. Flange offset is 21mm/33mm for the right/left side. For the same relative elongation of the spokes on each side one would need the ratio of diameters equal to the square root of the tension ratio; i.e., sqrt(21/33) = 0.80.

I considered the following spoke (all Sapim) combinations:
  • Strong (2.3/2.0 single butted) DS, D-Light (2.0/1.65/2.0 double butted) NDS. This most closely follows the diameter ratio of 0.8.
  • Strong (2.3/2.0) DS, Force (2.18/1.8/2.0 triple butted) NDS. Force will be thicker and stronger near the hub.
  • Force (2.18/1.8/2.0) DS, D-Light (2.0/1.65/2.0 double butted) NDS. Both DS and NDS spokes are thinner in the middle, unlike previous configs.
  • Force (2.18/1.8/2.0) DS, Laser (2.0/1.5/2.0) NDS. Probably too thin on the NDS, but both sides are thinner in the middle and the thickness ratio is followed. May stretch too much under the load.
What would you recommend? Am I overthinking it?
You are overthinking it a bit. I don't see an advantage to using different spoke diameters on the drive vs nondrive side. You'll get an advantage of going to the 2.3mm spokes on the DS and there's no detriment to having the same spokes on the NDS. It's just easier to use the same diameter of spokes on both sides. If you want a wheel with more even tension between the two sides, go for an off-center rim like the Velocity A23 OC. Watch the video in the link on what the off-center rim does for you. The off-center makes for a stronger wheel overall and the A23 is a good rim for what you want to do.
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Old 02-05-20, 09:37 AM
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I use the theory of a lighter spoke on the NDS, but I stay short of "equilibrium". (cross sectional area of the spoke vs tension)
Kind of a some is good, but too much may not be theory.
I figure there's MANY 10,000's of wheels built with same gauge on both sides that last until the brake track/hub wears out/dies.

I also love the OC rims. They reduce dish/equalize tension between sides extremely well.
THAT would be my 1st recommendation for a heavy rider.
I calculated that on the last one I built, if I had 142mm drop out width, I'd have no dish. (Velocity Synergy w/4mm offset)
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Old 02-05-20, 10:34 AM
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Several of my touring friends who weigh much less than 300 lbs have gone to 40-spoke rear wheels with success. Something to consider.
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Old 02-05-20, 12:17 PM
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I use the same double butted spokes on both sides of a rear wheel. The heaviest rider I have built for is 280 pounds.
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Old 02-05-20, 12:29 PM
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I'd probably use the same spokes on both sides.

I haven't used any of the 2.3/2.0 spokes yet, but have thought those would be a good idea. If the hubs support them (or modifying the hubs to work).

On the other hand, there wouldn't be a problem with using the "Strong" (2.3/2.0) spokes on the DS, and perhaps using Competition 2.0/1.8/2.0 spokes on the NDS.

There would be a good point. It is exceptionally rare to break a spoke mid-spoke, and it would almost always be due to underlying damage (does tossing a chain count?)

On the other hand, people occasionally break spokes at the J-Bend head (thus butting), as well as breaking them at the threads (more butting).

As far as I can tell, breaking spokes at the threads is often caused by bends near the nipple.

40h or 48h are harder to find, but worth considering. But, your 36h wheel should be strong if well done.
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Old 02-05-20, 12:35 PM
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How many broken spokes have you seen?

The huge majority break at the elbow bend. Using the most material that will fit through the hub flange holes makes a lot of sense to me. The rolled spoke threads make it necessary for the opposite end of the spoke to have a bit smaller diameter.
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Old 02-05-20, 04:05 PM
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My old Schwinn Superior had butted spokes with 1.65mm center sections on both drive and non-drive side. I relaced them (spokes were corroded and I wanted to build wheels) with new spokes: Center sections of 1.65mm on nds and 1.8 on ds.

Given that the 1.65 were Schwinn standard at the time, and Schwinn built stuff pretty rugged, I'm betting my upgraded wheels will be fine. I weigh 250.

I also had straight-gauge spokes (2mm?) on the rear of my paramount for 35 years. 36 spoke. No broken spokes. But I ride mostly on the road.

I suspect that anything butted (you want butted spokes - they will break less) with centers at or above 1.8mm on the DS, with 36 holes, properly tensioned, will work for you. If you want to bump the DS up to 2 to account for your off-road exploits that might give you some extra confidence.

One proviso: if you've been riding wheels with certain sized spokes and you've broken a lot, go one size thicker. Then build, ride, and don't think about it!

I agree with Sheldon about using different sized spokes. Probably not a big deal, but the theory appeals to the engineering training in my background. I also figured that going by what Sheldon says about bikes is a pretty good idea. So my rear wheel has different DS and NDS spokes.

Last edited by WizardOfBoz; 02-06-20 at 12:19 PM.
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Old 02-05-20, 04:32 PM
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You're overthinking it a bit. I think the middle sections of any wheel would have more than enough tensile strength--the main function of butting is to have the flex point be in a less vulnerable area than the hub flange or spoke thread. I'd build with DT Alpine IIIs or similar (2.34/1.85/2.0) all around for your wheel build. If you want go ahead and use a 1.6-1.7mm middle spoke on the DS, it will be fine with the amount of torque generated and will be under a more ideal elongation. Really 1.5 is fine but as the middle section gets thinner more care must be put into preventing spoke windup.
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