Old 07-18-19, 01:37 PM
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Carbonfiberboy 
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Bikes: CoMo Speedster 2003, Trek 5200, CAAD 9, Fred 2004

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Originally Posted by cyccommute
I took Carbonfiberboy's "correct tension" to mean the manufacturer's suggested tension (see below). There is no manufacturer's "suggested" tension that is meaningful. Basically, wheelbuilding is more art than science. You are correct in your assessment but there just no hard numbers that you can turn to.



Where do you find the "max specified by the rim manufacturer". I have yet to see any kind of chart for a given rim much less a /hub/spoke combination. There are sometimes generic tensions like Velocity's "110kgf and 130kgf" which covers 15 models of rims and 38 different diameters. A Velocity A23 is very different in construction and configuration than a DeepV or NoBS but they use the same spoke tension. That doesn't seem right.

Mavic doesn't even go that far and list no spoke tension ranges for their rims that are easy to find. If it were so important, I'd think they would put it right up front.

Park Tool has some tension recommendations but they are rather broad suggestions...and I look on them only as "suggestions". Giving a range like for the Bontrager rims, for example, of from 50 to 130 kgf is far too broad to be useful. That's 490 N to 1274 N (110 lb to 286 lb). That's a very broad range.

I also happen to work with people who operate a shop and not one of them can tell me what spoke tension to use. It's simple not listed.



Well I'm not sure what you are saying makes no difference. All of those factors make a difference to the durability of a wheel and they make a difference to the way the wheel is built. Again, there is no "specified" tension for rims...only ranges. And just running the tension up on spokes until they are as tight as you can get them can lead to cracking of the rim is some cases. The rim construction will make a difference.





That's only stiffness in one direction. Wheels are subjected to bending forces in multiple directions. Making the rim taller makes it stiffer only in the vertical direction not in the horizontal. The rim can be bent out of plane fairly easily and would be if it didn't have spokes resisting that out of plane bending. And the increase in stiffness is fairly small since aluminum (and most wheels are still aluminum) is fairly soft.

But even when the rim is taller, there's really no advantage to it being stiffer vertically. That's because the rim isn't attached to the spoke. The rim floats on the spoke and even though the rim is stiffer, it is still deflected upward when loaded. The spoke detensions and retensions as the contact patch is loaded and unloaded. The spoke still does all the work of keeping the wheel strong.



People seem to think that potholes are the cause of broken spokes. Nothing could be further from the truth. Hitting potholes at speed doesn't break spokes because the spokes aren't the thing hitting the pothole. Again, the rim is floating on the spokes. A pothole causes a momentary upward deflection of the rim and detensioning of the spoke followed by a retensioning. The cycle of tensions changes on the spoke are what break spokes and breakage of spokes usually isn't something that happens because of a one time event.
Really. The interaction of spokes and rims is much better understood than that now.

Spoke tensions are readily available from the manufacturer. Mavic says for front or DS rear, 90-110kgf. Obviously one could use 110 in back and 90 in front. Velocity thinks that theirs can handle higher tension: 110-130kgf, same locations.

Truly weird that the operators of your bike shop are unaware of published spoke tension specs. Don't know what to say to that. Took me 3 minutes to find the above two specs on the web. If you can't find it on the web, an email works well. Put the replies in a file for reference. Manufacturers have a strong interest in their rims performing reliably.

I strongly recommend using the rim manufacturers specs and not altering tension depending on the number of spokes, type of spoke, the particular rim from that manufacturer, or the weight of the rider or gear. I've never seen a broken spoke that was not on an undertensioned wheel. I have seen a cracked rim which had the specified spoke tension. Rolf had a run of tandem wheels which were poorly engineered. Yeah, don't use that rim or maybe that wheel next build. Manufacturers do make mistakes, but they're rare.

"running the tension up on spokes until they are as tight as you can get them" is a straw man. No one here has suggested that. One follows the rim's specs, simple as that. IME running 110 kgf on DS works at least up to 400 lbs. and no sense using less for lighter loads. I don't think any rims are rated lower than that. I use 100 kgf in front simply because why not.
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