truing carbon rims

[jonny jeez]

After over a year of hard work, my rear 50mm carbon rim has developed the slightest of wobbles....its tiny but it is there.

Is trueing carbon exactly the same as any other material, or do I need to cast some special spell or repeat some sort of incantation.

I thought it best to ask first before setting at it with a spoke spanner.

 

[Yellow Saddle]

Truing carbon wheels is no different from trying aluminium or steel wheels. However, carbon rims cause more spoke tension variation than aluminium rims because the material is less uniform. Thus, don't attempt to true them by listening to spoke tone or using a tensiometer. Simply true - as allw heels should be trued - by looking at run-out.

Before you start, find the spoke that has lost tension and carefully examine the spoke hole for cracks. Spokes don't just lose tension, there's a reason for that and with carbon rims it is usually a crack. Obviously on poorly tensioned wheels some spokes can come loose by themselves, but always be suspicious.

ON a 50mm wheel it is unlikely that the wobble will be local to one spoke only and will typically span 3 or 5 or any other uneven number multiple. Find the epicenter of the wobble but also work on the adjacent spokes to the central one. A 50mm piece of carbon rim is one stiff beam and one spoke is not man enough for keeping it in line.

Edit: Stiff beam, not still beam.

 

[jonny jeez]

Truing carbon wheels is no different from trying aluminium or steel wheels. However, carbon rims cause more spoke tension variation than aluminium rims because the material is less uniform. Thus, don't attempt to true them by listening to spoke tone or using a tensiometer. Simply true - as allw heels should be trued - by looking at run-out.

Before you start, find the spoke that has lost tension and carefully examine the spoke hole for cracks. Spokes don't just lose tension, there's a reason for that and with carbon rims it is usually a crack. Obviously on poorly tensioned wheels some spokes can come loose by themselves, but always be suspicious.

ON a 50mm wheel it is unlikely that the wobble will be local to one spoke only and will typically span 3 or 5 or any other uneven number multiple. Find the epicenter of the wobble but also work on the adjacent spokes to the central one. A 50mm piece of carbon rim is one still beam and one spoke is not man enough for keeping it in line.

Thanks.

I whipped the tyre off and found that the rim is as true as the day I bought it. Unfortunately my brake block had been touching the edge of the tyre and caused a wear, which had bulged out a tiny bit . Stupid mistake that has cost me a tyre, but I am glad I found out today and not whilst braking down some steep hill.

Cant work out how the block got that high, I am pretty careful about brake adjustment...odd

 

[Drago]

Excellent advice from YS.

 

[User6179]

Cant work out how the block got that high, I am pretty careful about brake adjustment...odd

Do you use different wheels on the bike , amazing the difference in sizes on supposedly same size wheels .

 

[jonny jeez]

Do you use different wheels on the bike , amazing the difference in sizes on supposedly same size wheels .

I do in the winter but that change also requires a swap in blocks (the winter runs are aluminium).

I suspect it was just stupidity when I swapped the calipers a month or so ago...but I feel daft for making such an obvious mistake

 

[Milzy]

Truing carbon wheels is no different from trying aluminium or steel wheels. However, carbon rims cause more spoke tension variation than aluminium rims because the material is less uniform. Thus, don't attempt to true them by listening to spoke tone or using a tensiometer. Simply true - as allw heels should be trued - by looking at run-out.

Before you start, find the spoke that has lost tension and carefully examine the spoke hole for cracks. Spokes don't just lose tension, there's a reason for that and with carbon rims it is usually a crack. Obviously on poorly tensioned wheels some spokes can come loose by themselves, but always be suspicious.

ON a 50mm wheel it is unlikely that the wobble will be local to one spoke only and will typically span 3 or 5 or any other uneven number multiple. Find the epicenter of the wobble but also work on the adjacent spokes to the central one. A 50mm piece of carbon rim is one stiff beam and one spoke is not man enough for keeping it in line.

Edit: Stiff beam, not still beam.

Do you need a torques spoke key for carbon wheels so you don’t over tighten & shatter the carbon?

 

[Yellow Saddle]

Do you need a torques spoke key for carbon wheels so you don’t over tighten & shatter the carbon?

A torque spanner for that job doesn't exist and isn't needed either. Howevler, you do need to iunmderstand the relationship between the tone of a plucked spoke and it's tension. Unless the rim manufacturer gives you a maximum spoke tension, youi're on your own in fiding and staying below maximum tension.

The problem with carbon wheels is that you cannot pre-stress the spokes. This is a process where you stretch the spokes forcefully beyond the yield point, in order to stress-relieve them. Aluminium rims can handle the over-tension, but carbon wheels cannot, therefore they are not stress relieved and the spokes don't last as long as on aluminium spokes.

 

[Milzy]

A torque spanner for that job doesn't exist and isn't needed either. Howevler, you do need to iunmderstand the relationship between the tone of a plucked spoke and it's tension. Unless the rim manufacturer gives you a maximum spoke tension, youi're on your own in fiding and staying below maximum tension.

The problem with carbon wheels is that you cannot pre-stress the spokes. This is a process where you stretch the spokes forcefully beyond the yield point, in order to stress-relieve them. Aluminium rims can handle the over-tension, but carbon wheels cannot, therefore they are not stress relieved and the spokes don't last as long as on aluminium spokes.

Interesting stuff. Well Hunt spokes are terrible. As the rim is delaminating the LBS will try to warranty a new rim and re-build with some quality spokes. It might cost me £60 but it’s an upgrade.
The rim might have got hot some how not sure. It happens on rear cycle racks from hot exhaust fumes I’m told.

 

[Ian H]

I don't really understand why anyone who isn't racing buys carbon rims.

 

[Webbo2]

I don't really understand why anyone who isn't racing buys carbon rims.

Because they look nice and they make a nice swooshing sound.

 

[Milzy]

I don't really understand why anyone who isn't racing buys carbon rims.

I won’t buy anymore. I’ll stick to some hand built aluminium with quality hubs. I’m selling my carbon bike & collecting a mint CAAD10 tomorrow.

 

[Ian H]

Because they look nice and they make a nice swooshing sound.

That's fine if your bike is just a toy. Mine have to be reliable over long distances.

 

[Milzy]

That's fine if your bike is just a toy. Mine have to be reliable over long distances.

To be fair many carbon wheels are bomb proof enough even cheap china ones are decent quality now. It’s Hunt wheels that have weak spokes. You can still knock out 200 milers on them but you’ll end up with a buckle at some point with Hunt carbons.

 

[ColinJ]

Because they look nice and they make a nice swooshing sound.

I actually dislike that sound, especially because I hear it all the time as faster riders overtake me!

I will stick with aluminium rims.