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Retrue carbon rim after crash?

Posted: Sun May 26, 2019 9:56 am
by Alexandrumarian
Last year been in a frontal crash with a car. Wheels were Bora 35 tubs. Front wheel broken, i flew head first. Rear end seemed pretty much untouched except a saddle scrape.

Despite this, the rear wheel went out of true. Not a lot but a section went to the right (Ds) by a couple mm. The spoke tension remained as it was (park meter fwiw). Rim seems intact, no cracks, sounds good when tapped.

My guess is that i can fix it pretty easily without ending up with nasty tension anywhere. I have built a couple wheels before. Still, i am concerned there might be some structural problem with the rim or maybe the hub. The wheel spins freely but i cant take out the freehub. Probably corroded on the axle rather than stuck from deformation but who knows.

Any thoughts? Hang it on the wall as hub/spoke spares or true it and ride it happily? I know i might sound like a pansy but i value my hide a lot....

Thanks!

Retrue carbon rim after crash?

Posted: Sun May 26, 2019 9:56 am
by Weenie

Re: Retrue carbon rim after crash?

Posted: Sun May 26, 2019 10:32 am
by mattr
If the wheel spins freely with no wobbles the hub will be fine. (Make some time to free up the freehub though, when you have some time and patience!)

Truing a carbon wheel is just like truing a aluminium rimmed wheel, just more expensive.

(Be careful if its campags G3 lacing, that can cause headaches in less experienced builders, it takes time and patience. Unless you do them all the time. I've done one, ever. Next time someone asks, i'll get them to send it off!)

Re: Retrue carbon rim after crash?

Posted: Sun May 26, 2019 12:30 pm
by Alexandrumarian
Thanks. I'll keep trying with the hub. Probably next I'll put it in a vise and littly tap the axle with a wooden block.

As for the spokes, yes triplet. Good part is the problem area is right over a group. It might fix simply by tinkering those 3 spokes.

((What is stopping me to try it is the lack of a suited key atm))

Re: Retrue carbon rim after crash?

Posted: Sun May 26, 2019 2:27 pm
by WinterRider
mattr wrote:
Sun May 26, 2019 10:32 am
If the wheel spins freely with no wobbles the hub will be fine. (Make some time to free up the freehub though, when you have some time and patience!)

Truing a carbon wheel is just like truing a aluminium rimmed wheel, just more expensive.

(Be careful if its campags G3 lacing, that can cause headaches in less experienced builders, it takes time and patience. Unless you do them all the time. I've done one, ever. Next time someone asks, i'll get them to send it off!)
Be interesting if you've the time and inclination... to relate the truing of the G3. I recently did a 12-6 albeit alloy rim... patience required.

Re: Retrue carbon rim after crash?

Posted: Sun May 26, 2019 2:44 pm
by mattr
Not much to say really, just went far slower and steadier than i would with anything else. And treated each group of three as a unit, rather than each spoke individually.
I've heard that the rims, when new, are deliberately made out of round to account for the grouping of the spokes as well, the one i trued wasn't bad enough to see any effect of that, but it's just something else to bear in mind.
There are FAR better qualified people on here to explain the nuances of truing a G3 wheel.

Re: Retrue carbon rim after crash?

Posted: Sun May 26, 2019 3:11 pm
by WinterRider
I made that inquiry as at times another manner/set of words relating techniques brings new insights to mind. Thanks for the reply.

Re: Retrue carbon rim after crash?

Posted: Sun May 26, 2019 3:36 pm
by Calnago
I’ve always been curious as to what actually goes into building a G3 wheel, especially a carbon rimmed one. I know that, as mattr says, an aluminum G3 rim starts out of round and the final tension of the spokes “pulls” the rim into round at the spoke areas, but I don’t know if it’s similar with the carbon rims. I’ve only ever broken one spoke on a Bora (rear), and I stopped riding immediately (too out of true to ride anyway). I have the proper spoke kit on hand so once home I replaced the one spoke and brought it back into tension after reading the tension on the spokes of a good, unbroken Bora for comparison. It’s been perfect ever since and that happened years ago (it’s a 2010 wheel).
It may very well be Wall Art at this point, so might be interesting to play with it for awhile just to get a feel for how it reacts while trying to bring it back to life. I just don’t know at what point it needs to be trashed versus being able to be saved.

Re: Retrue carbon rim after crash?

Posted: Sun May 26, 2019 4:40 pm
by Alexandrumarian
Light bulb moment, I realized a while ago I got myself a dremel with various accesories - meaning I could enlarge my 3.5mm spoke key easily (I tried a while ago with a file and it was futile) After a few minutes it was accepting the 4mm nipples. What I quickly found out is that the nipples were very strongly locked. I ruined a couple aero spoke holders from the twisting before unlocking a few threads.

It seems to me the system is very sensitive. A half turn or so on the NDS spoke moved everything way over the line to the left. In the end I tinkered a little bit with 7 spokes (2 didn't unlock) from 3 groups and now it seems to turn pretty reasonably true (a few high spots of 0.5mm rather than one big 2mm hump)

I'll keep an eye on it and report more later. Need to wash the rim and look at it in detail with a magnifier for cracks/wrinckles etc (yeah I'm like that)

Re: Retrue carbon rim after crash?

Posted: Mon May 27, 2019 3:38 am
by alcatraz
What surprised me was that you didn't measure any uneven tension despite the wheel being untrue because of one spoke.

One hypothesis is that the rim had a slight out of round coming out of the factory resulting in one overtensioned spoke that later loosened in the crash.

Re: Retrue carbon rim after crash?

Posted: Tue May 28, 2019 2:19 pm
by WinterRider
U-boobed some video's of carbon hoops... the number of rim failures riding surprised.... must be a fairly common event.

Who wants to go down in that manner? :noidea: Is it prudent to ride a wrecked carbon hoop... but then.. who, what.. how does one decide what is safe and what is not........

Re: Retrue carbon rim after crash?

Posted: Tue May 28, 2019 4:24 pm
by Alexandrumarian
Who knows what happened. Maybe some spoke heads dug a bit in the alu or some nipples in the carbon. I definitly don't see any cracks or anything. I guess the wheel sustained the bike falling down after doing a loop in the air. I think pro bikes see this all the time, i doubt they bin them if no cracks or creaks emerge.
Wouldn't be the end of the world if it sits on the wall as I got a replacement from the insurance. Still, my rides are half flat half hills and since I'm heavy, i need a 32 cassette. It kinda sucks on the flats so having two rear wheels is ideal for me, 12 - 25 and 11 - 32

Re: Retrue carbon rim after crash?

Posted: Wed May 29, 2019 2:41 pm
by WinterRider
"I think pro bikes see this all the time, i doubt they bin them if no cracks or creaks emerge"

Read the yards and yards of fine print one can not read even w specs.. that comes w plastic bikes. The 'lawyer layer'.. carbon makers and
sellers know very well the risks of running that plastic after crashes.. after impacts of 'minor' nature.

One's well being is not worth any risk w plastic components.

Re: Retrue carbon rim after crash?

Posted: Wed May 29, 2019 2:41 pm
by Weenie

Re: Retrue carbon rim after crash?

Posted: Wed May 29, 2019 3:52 pm
by mattr
Pro teams visually inspect then true the wheel if it's practical.