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Giant TRX-0 Carbon Wheels - basically DT240 straightpull hubs (tick should be fine), sapim super spokes (tick should be fine) and a hookless 30mm carbon rim that looks awfully similar to the older XMC1200 (now XMC1501's I think) on my other bike (tick shouldn't be an issue). Rimpact insert. About 19-21psi depeding on conditions and I'm about 75kg.
First time I broke one I was just pedalling up a slightly stony climb - we replaced with fibre spoke and finished the ride (rocky, lakes) just fine. I replaced with a CX-Ray and retrued.
This week I threw one descending Nan Bield (cleaned it for the first time). I had a wheelbuilder in Kendal rebuild with a D-Light and retrue the wheel. Didn't actually notice - finished the ride and rode Helvellyn twice in one day (inc Birkside) before I noticed so the wheel is pretty robust otherwise. This spoke nowhere near old broken one.
Yesterday took one out coming down Cut Gate South. Wheel held up but same thing - broke at nipple entry. This one opposite the last one.
I have some cx-rays from the last one but I'm getting pissed off with having to retape a whole wheel every time I ride.
Any ideas?
Sounds like a cra wheel build. What's the tension like? Even, uneven? Loose?
Had the whole wheel retrued in Kendal by a well-reviewed pro wheel builder - he said all the tensions were even and when you play them like a tuning fork there are no off notes (I don't personally have a spoke tension meter).
If you're continuing to break spokes, replace all the spokes.
If they are starting to break randomly, it could indicated that if the initial build wasn’t evenly tensioned, then the subsequent breakages could have over-stressed the others and you’ll just be chasing your tail with future breakages. The only option might be to have the wheel rebuilt with new spokes.
Where are they breaking?
I had a wheel that all the nipples just started failing after a few years. It had been trued/checked by LBS and was generally in ok condition.
Hang on so now it's got a mixture of super spokes (PG?) One CX ray and one D-lite?
IME mixing spokes just leads to uneven stresses and another spoke going ping at some point, replace like for like if you can. It reads as if you've got one or two spokes with a different cross section and different tensile strength, Which just moves the higher stress point about...
Also were they possibly a bit over tensioned to start with?
Edit: actually a quick Google suggests the super spokes are 1.8/1.4 butted (!), The CX ray 2.0/1.8 and the D-lite 2.0/1.65...
It might be musical but the tensions will be wildly variable if you've got all of those in there, and if the carbon rim is nice and stiff may just be masking the issue/helping to over-stress certain spokes... I'd re-lace the whole wheel with CX Ray (assuming sapim are your spoke of choice). Out of interest what's the spoke count?
If you’re continuing to break spokes, replace all the spokes.
This
28H front and rear. Yeah, those do seem a little light for smashing down rocky descents.
@matt_outandabot
All at the nipple join.
...and when you're replacing all the spokes, have a good look at the carbon rim in bare form - is it straight for trueness and round. A wide rim like that can be so strong that if it's off on its own out of the mould then making it straight and round on building can introduce unwanted stresses- its normally not this.
Also, does the drilling of the spoke holes in the rim appear suitable for how the spokes end up exiting towards the hub?
The first one letting go so easily suggests those 'super' spokes are just too damn slim for the application and intended more for road wheels. 28 should be an adequate number, but they've got ~25% less cross section than the CX ray, assuming sapim use the same material that's simply 25% more stress on each spoke...
The breaking at the nipple is probably just because you're getting more elongation from the butted sections of each spoke, and the spoke that lets go is the one most stressed as the wheel cycles the loading around it's circumference, the end of the thread on that particular spoke ends up being the focal point...
Yeah, I'd echo the suggestions for a re-lace, ideally with slightly chunkier spokes...
If it was an aluminium run I’d suspect it had had deformed. I don’t think carbon can do that.
Speculation based on physics and some reading on how wheels work.
If the spokes have different diameters the wheel can be built with even tension. The problem is when you load it. When you load the wheel the bottom the spokes reduce in tension. Here the thinner spokes will have a smaller reduction in force for the same rim distortion. This could lead to uneven forces onn the rim
Does anyone know if carbon rims are less strong when pushed hard? Or if they need building differently? I thought a key feature of the way a wheel works is the flattening of the rim at the bottom reducing the tension in the spokes at the bottom. A really stiff rim must change how this works. Does it put more reliance on the top spokes stretching. The thinner spokes will have less tension than the thicker soles at the top again leading to forces you don’t want
But any way you need a rebuild with new spokes
Cheers, thanks. Time to pony up.
What spokes?
I'm not going for CX-Rays on the whole wheel - it's not worth it for my enduro bike. Anything to persuade me from D-Lights all around? Lasers?
Sapims all seem cheaper for a build than DT.
I’d just use a decent 2.0/1.8 butted spoke or similar.
DT competition / ACI double butted (cheapest option in the UK / whatever the Sapin equivalent is.
what's the spoke count btw ?
I’m not going for CX-Rays on the whole wheel – it’s not worth it for my enduro bike. Anything to persuade me from D-Lights all around? Lasers?
Sapims all seem cheaper for a build than DT.
I reckon the snapped spokes you already experienced should be the dissuading factor TBH.
Is it really worth saving a few grams for D-lites over CX rays 0.15mm skinnier in the middle?
As for Laser; the butted section is 1.5mm, only 0.1mm more than the Super, are you aiming for an absolute edge case?
I reckon a bit more margin is worth a barely noticeable extra few grams TBH.
Perhaps talk to your wheel builder see what they suggest?
In Sapim it looks like the Race is a 2.0-1.8-2.0 spoke. You’ve only got a 28 spoke count on an enduro wheel - why go for lighter / thinner spokes - especially where you’ve already had problems with snapping?
The avoidance factor for cx-rays was the prohibitive cost. D-Lights are stronger and thicker than Supers (what keeps breaking), Lasers rated significantly stronger than Supers (but yes, similar thickness).
I'll go into my bike shop with the wheel next week.
Brass nipples should also help...
D lights are a great spoke and are usually my spoke of choice for MTB wheels.
I had this with a GT. It was known that there was a batch of badly-built wheels in one year so everybody was breaking spokes. I had the wheel rebuilt with new spokes and all was well.
+1 to most people's opinion, once a couple have gone they'll likely all start going, this is fatigue.
2.0/1.8/2.0 should be fine - it is for most people, that said I generally use Lasers (2.0/1.5/2.0) with no problems - a CX-RAY is just a rolled Laser after all.
Ugh, my lbs only uses DT. What are the equivalents?