Wrecked spokes? How?

lvquestpaddler

Strange one, got me well baffled this has. Got new DT wheels for the bike and relegated the deore/aci/mavic717's to road wheels for it. Used the 717 wheels for 15 miles with a 7 spd cassette and a spacer on the inner side of another trainer bike I built up, before putting the 7spd cassette on an even older wheel which is now on the trainer. I put a standard 11-32 9spd back on the 717 wheel(in fading light...) and it's not been used since.
Been tinkering with 2 cassettes to make one low geared primarily and another more road geared, swapping sprockets etc, and to my horror tonight I removed the 9sp standard cassette to put the road friendly one on and all 8 spokes on the outer drive side hub have been mangled to half their width. Yet I've never had a chain come off and wedge on the inner side, ever. and never had any scraping or grinding so I can't figure out where the damage has come from?? Could it be the el-cheapo Acera 7/8spd mech? But how could that get behind the sprocket of the 7 spd(lowest is 28T) to do the damage?
Does anyone know how to work the DT calculator- ie what size spokes would I need for deore 525 hubs and xc717 rims rear drive side? I looked at the site but computer says no...
I'd rather take a chance and replace each one by one than have a catastropic failure

nicklouse

pics. but i would say chain damage.

just input the required info with the intersections (cross patten) or try other spoke calcs. see tech links sticky.

cavegiant

Sounds like a spoke troll went for them.

Fix the wheel, lay out troll traps and the problem should go away.

ds690

Check that the back side of your cassette carrier is not hitting the spokes. I had to fit a 1mm spacer behind my xt cassette to get enough clearance on my Dirty Flea hub.

lvquestpaddler

Took it to work and removed a spoke, quick trip to the LBS only had PG in black but was assured would be no problem mixed with DB spokes(?! Hope this is true....)
Have replaced all them one by one seems simple enough, the wheel is still true, willl give it a blast tomorrow and hope the spoke popping gremlins haven't taken over- pinged them with a screwdriver and the tone seems pretty similar.
LBS said it could only be the chain that did it. So, still baffled unless someone has "borrowed" it without my knowledge and trashed it!
The mech has never been off it until the LX was replaced with the 7spd acera, and the low stop screw needed adjusted to let it on to the lowest gear which means it can't have been this.
Maybe it's been like this for ages and I've only just noticed my "time bomb" GT! :oops:

cavegiant

don't forget to set the traps