Forum menu
A couple of months back, I rebuilt my big bike wheels. New WTB KOM125 rims on my old DT240 hubs, new Sapim D-Light spokes. Built up nice and easy, tensioned up to the max they recommend for the rim, which equates to about 20 or 21 on my Park tension meter. Got it almost bang on with regard to variation per face of the wheels. (and properly tension relieved)
Fast forward to Saturday night and I was changing brake pads when I noticed that maybe 6 spokes on the non drive side of the back wheel were completely floppy and the rest were not all that tight. Cue some late night nipple twiddling. (Fnarr!)
So what's caused this? Normally I'd say insufficient spoke tension, but I'd done the drive side up to the suggested max, so the NDS is always going to be looser. When I retensioned it, I've done it up to the max again, but this with the tyre mounted, as obviously the pressure "shrinks" the rim a fraction. But this still puts the drive side (nearer 22 on the meter this time) way tighter than 16-17 on the NDS side - equates to between 40 & 45% difference).
Any ideas? I obviously don't want my wheel going baggy again, but neither do I want to end up cracking the rim through overtensioning it.
Thanks,
J
Super-skinny spokes can be quite stretchy, plus the Park gauge tends to over-read so probably a combination of the two?
Clearly the tension is too low, take it up a bit.
nearer 22 on the meter this time) way tighter than 16-17 on the NDS side - equates to between 40 & 45% difference
Not a wheelsmith by any stretch but I work to a 70/100 tension ratio and it works fine for me (Which is close to what you have)
Are you ending up twisting the spokes so they then 'unwind' when ridden reducing tension?
Lots of leaning on the rims worth the hub centre on the floor helps plus pulling parallel spokes together as well.
I am not familiar with d-light but i can tell you that super butted spokes dont work on rear wheel for powerful riders, they are too elastic. I tried DT revolution on a rear wheel and had nothing but problems, great on front wheel though.
It appears you do not have enough tension in the wheel I always tension the drive side as much as i can, the wheel starts to pringle if you put too much tension on it, at which point you know you have hit the limit and can back off a little.
Are you ending up twisting the spokes so they then 'unwind'
Nope. I destress them regularly during the build
I am not familiar with d-light
Its Sapim's equivalent of the DT Supercomp. So light, but not silly light. For the record - I'm 65kg, so no powerhouse, although I'm not known to hang around DH.
I always tension the drive side as much as i can
Is that not just going to end up in premature rim failure. I presume they give max spoke tension for a reason? The previous Arch rim cracked around most of the eyelets and that was done up bloody tight (not built by me).
This is far from my first wheel build - reckon I must be 15 or 20 in by now and it's the first one I've had issues with. Will stick a bit more tension on and see what happens.
De-stressing and preventing wind-up are related, but not exactly the same. How are you preventing wind-up?
I would suggest putting some masking tape 'flags' on the spokes a couple of inches from the nipple. (as close as you can to the nipple without them getting in the way of the spoke key). If they start to twist when you wind the nipple, then try gripping the spoke with some pliers with elastic bands over the jaws.
Are you running the i25 rims in 29er? The DT 240 hubs have really awful flange spacing. That, paired to a shallow rim and light spokes, and you have a recipe for a wheel that struggles to keep tension. The only pair of wheels that I've ever had a problem with this was some 240 road wheels with revo spokes. You may have some luck trying race spokes on the DS. But ultimately the bracing angle may be against you.
IMHO if it cracks around the eyelets then it is probably not a very well designed rim, the tension should start the collapse the section of the rim before the eyelets start to fail.
I guess you can go too far in spoke tension, but I don't have a spoke tension meter so I do it more from feel.
For certain if the spokes are unwinding then this is because because the force being exerted on the rim while riding is exceeding or getting close to the spoke tension, and this is of course a scenario which will cause premature failures as spoked wheels get their strength from being in constant tension and hate being in compression.
You've probably built more wheels than me, thinking about it I built my last MTB pair over 10 years ago! Then again it only has 28 spokes front and rear, I weigh over 90kg and don't have a reputation for riding smoothly, and they have remained dead straight throughout all those years so I must have done something right.
Well it's not the spokes.
90+ kg rider on Arches built by myself using Dlights and no issues with spokes coming loose. Tension was also set using a Park meter.
just ramping up the tensions a terrible idea.
coupled with the park tension meter being absolutely bollocks at giving accurate numerical readings.
its good for determining an even tension around the wheel at a repeatable number - but what that number is is largely irrelevent as it doesnt seem to relate to anything with any great accuracy other than its self.
Can anybody demostrate the readings on Park tension meters are bollocks?
What are you putting on your nipples*?
*pfwaaaargh!
Can anybody demostrate the readings on Park tension meters are bollocks?
I think the problem is that they are often wildly mis-calibrated out of the box. If you can get it calibrated, they're fine.
can any one demonstrate they are not ?
the one i tried gave wildly different readings to a dt swiss tensionometer - which gave ball park readings more comparable to what my hands would tension a wheel too before sending it out the door.
with the park the spokes were tensioned like worn out knicker elastic.
I still didnt buy either tool.
ps linseed oil for nipples - just dont leave it on rags around the workshop
Yeah, I have a pair of wheel from SJS and they came with Linseed oil which was going to be my suggestion too. Never been touched, done countless thousands of miles loaded touring.