Carbon rims & spokes

epo.wks

Am I correct in my assumption that a carbon rim will not buckle in the same way an alloy one would?

I ask because the back spokes on my Campag Boras are making a pinging sound & I'd like to take a look at them without making the wheel resemble a pringle!

I'm not looking to hang off the spoke key so can confidently say that the risk of cracking through applied pressure is low but would be interested in hearing from anybody who's tackled similar spoking issues.

cycleclinic

Carbon rimmed wheel do buckle quite well if the spoke tension is not even. If you are not familar with truing wheels then starting on a bora is not a good idea, you may round the nipple off e.t.c take to a shop if you have to ask, learn on something cheaper and easy to fix if you get it wrong.

epo.wks

I have built wheels in the past but we're talking years ago and nothing carbon, only alloy rims. However, saying that, I am inclined to agree that it may be an LBS job.

cycleclinic

you will also need a spoke holder for bladed spokes. The cost of that pays for the truing at the LBS.

smoggysteve

A) you take wheels to lbs - they take on job, they break em they fix or replace em

you do it. You break em - you're f@#ked.

term1te

I had a foot/pedal/something go into my front wheel, 50mm carbon rims, during a sportive. One spoke broke, another badly kinked, and the rim went at least 1cm out of true. I opened up the brakes and finished with the rim rubbing on the pads. I replaced the two damaged spokes and re tensioned the whole wheel, its run true for 18 months since. I stopped the bladed spokes rotating as I tensioned them by holding the flat section nearest the nipple with a small adjustable spanner. I was amazed that the carbon rim survived whilst a spoke broke.

I'm not sure about buckling, but they can bend alarmingly, and survive.

epo.wks

As I said, the buckling thing was merely an assumption based on never having seen a bent carbon frame or wheels, only snapped/badly cracked ones!

Interesting to hear that they do, in fact, buckle. Would never have guessed it.

ugo.santalucia

epo.wks wrote:

As I said, the buckling thing was merely an assumption based on never having seen a bent carbon frame or wheels, only snapped/badly cracked ones!

Interesting to hear that they do, in fact, buckle. Would never have guessed it.

Stiffness is not an infinite concept... there are degrees, it bends less than other materials, given equal section, but it still bends

epo.wks

That's a fair comment, Ugo.

desweller

Where CFRP is not so clever is that it doesn't plastically deform like a metal. Your rim will elastically deform as a result of the spoke tension imbalance, but you don't need to exceed the yield stress of the material by much to get it to fracture; aluminium or steel will deform quite a lot before fracturing.

cycleclinic

In fact carbon rim are quite elastic, if you plastically deform a alloy rim by spoke tension inblance you are trying hard and the rim is just as ****** as if you fractured it. I think you have to quite hamfisted to damage a rim by messing up on spoke tension.