Spoke Question: Rust

[1chubby cycler]

So I bought a new bike back in Sept '10 and I have since put about 1,000 miles on the bike and have recently (last 2 months) been breaking spokes every other ride. I'm not rough on my bike and I try to avoid as many bumps, cracks, holes, etc. as possible on the road. The place where I take my bike said that usually you will break a spoke, and then 1-2 more will break before the rim is "back to normal" again. He then proceeded to replace the wheel and noticed that there was a little bit of rust on the spoke and tells me that rust can weaken the spokes and tends to make them snap easier. (I live about a mile away from the coast and do most of my riding up and down the coast in my area, so I realize my spokes are prone to rust due to the atmosphere near beaches) Anyways is this true? The rust on my spokes seems to be only surface oxidization and I have a hard time believing it would make my spoke that much weaker. And are spokes more prone to snapping on a wheelset with the amount of miles I currently have on mine?

Thanks

 

[Paul Walnuts]

I'm thinking that time spent travelling is not the issue compared to time spent in sea air conditions. If you're not abusive on your wheels I don't see why the can't last you a good few multiples of years, like at least 3 years.

 

[tafi]

I strongly doubt that rust is the problem. To trace it as a cause you'd need to see corrosion at the precise points where the spokes broke, and I doubt that would be the case.

Though you haven't said where on the spokes the breakage occurred, my first guess would be that the spokes broke around the elbow, at the thread, or at some point where the spoke had previously been damaged. This is a common indication of fatigue failure.

I'd also be willing to bet that the broken spokes were on the non-drive side of the rear wheel (where spoke tension is low).

Most commonly this occurs on wheels which are machine built, a process which often results in poorly balanced (and too low) spoke tension and accelerated fatigue.

 

[1chubby cycler]

Thanks! The three spokes I have broken have all been on the non-drive side and have all snapped about 1/4 of the length of the spoke going up from the nipple. I looked at my rim and of the three spokes that have broken, it has been in 2 different places.

BTW I figured it wasn't the rust bc I can clean it off and underneath each patch of rust the spoke looks fine and undamaged.

 

[cloudhead]

It wouldn't be rust if it's only 2 years old.

There are so many grades of spokes that it's hard to say, but some spoke manufacturers are more concerned about ease of wheel building than they are about quality, and when that happens, the spoke quality drops down.

DT spokes notoriously changed their spoke design in this way in 2000, and had to return to a more traditional design in 2006 due to the low quality. This article by a top wheel builder might provide some insight into your investigation.

http://www.peterwhitecycles.com/DTspokes.htm

If you can, find out what spokes are used on your bike (sometimes available on the bikes spec sheet) and post a thread about that brand and you'll probably get some more detailed opinions of the spoke.

 

[tafi]

That was the other caveat I didn't mention. My argument above refers to the use of good quality spokes (as Cloudhead has pointed out).

Spokes fail (by fatigue) at stress raisers: sudden changes in shape or section and also material defects.

The first two strees raiser types are usually visible and cannot vary that much whether the spoke is of good or poor quality. As mentioned above they are usually the elbow and the thread. Material defects can occur anywhere in the spoke and are usually NOT visible.

Good quality spokes tend to have few, if any significant material defects (DT, Sapim, ACI are the main brands for this reason). However, this is only one half of the story. The other half is how well built the wheel is (which is detailed above).

Poor quality spokes are also prone to failure at elbow and thread but, becasue they often carry material defects, can fail at almost any other point as well.

A fourth kind of stress raiser is spoke damage. Any nick or scratch can act as a nucleus for crack development. This kind of failure is more common on the drive side as a poorly adjusted derailleur can result in the chain being shifted into the spokes and damaging them.

The creation of good quality spokes relies on the type of steel used, the method by which the wire is drawn and the process of finishing. Rolled threads are stronger than cut threads and spokes which are butted by forging are much stronger than those which are butted by grinding.

 

[cloudhead]

Hey there, me again. I was just talking to my mechanic and asked him about this while we were killing time, and he said your spokes are probably twisted. Tafi's 1st guess of a hastily built wheel also gets my vote.

When adjusting, an expert wheel builder will grip the spoke halfway with a tool while adjusting it. An inexperienced mechanic will just start truing away without thinking of all the physics involved. You might want to seek out a shop near you that has a wheel building expert that inspect the spokes and make sure nothing else goes wrong.

-Court

 

[revolveteam]

Hi,

When adjusting, an expert wheel builder will grip the spoke halfway with a tool while adjusting it. An inexperienced mechanic will just start truing away without thinking of all the physics involved. You might want to seek out a shop near you that has a wheel building expert that inspect the spokes and make sure nothing else goes wrong.

bootcamp course

 

[1chubby cycler]

Thanks guys for all your input I appreciate it very much! If the problem continues, I'm gonna look into finding an expert wheel builder in my area and have him take a look at it.