HELP - Wheel Failure Analysis

[RustyIron]

Ok you bike mechanic experts! If you have a few minutes, please look at the pictures that resulted in my mishap.

The group of four pictures is at http://www.rustyiron.com/wheel
I will try to embed the pictures in this message.

Picture 1: This is the failed front wheel. Note taco shape and break in rim.


Picture 2: Side view of broken rim


Picture 3: End view of broken rim


Picture 4: This is the BIG QUESTION. Further examination revealed a fracture in the rim, far from the other break. Look closely, and it appears that metal has "wiped" along the fracture, is if it has been there for a while.


The result of this failure is at http://www.rustyiron.com/ugly As you can imagine, I want to figure out as closely as possible what happened and how it can be avoided in the future.

Could the visible fracture have pre-existed the catastrophic failure? Could a fracture at the point of failure caused the collapse?

What am I overlooking, and what can be learned from this?

Thanks for your input,
Rob

[foofighter]

im no Metallurgical expert but you can see there was some fatigue that cause the wheel failure. it looks like you use rim brake too from the looks of the sidewall of the rim. could this have brought it on? or was there just a bad batch of extrude metal when they made the rim? that's crazy though

[2wheel_lee]

Low spoke count wheels rely on high spoke tension - particularly with those Rolfs. And in the case of those Rolfs, the spoke tension is pulling in one small area of the rim, and not displacing the load over a larger area, which is more common on other low spoke count wheels. As a result, as you see, is the rim failing in the area of the spokes. The reason it failed on the sidewall where it did is because the rim brakes did wear a slight groove in the rim.

This design of these Rolfs was very popular a few years ago, but has mostly faded away due to the problem of this design.

Sorry, I'm about to go to bed, or I'd explain it a little more. Even better if I could illustrate the areas of the rim under tension as well as the areas of the rim that are not under tension (no spokes) but under compression (from the spokes pulling in on the nearby small sections of the rim).

I hope you weren't injured as a result of the failure.

[OldDogDan]

This is actually not uncommon. Rim brakes will eventually weaken the rim. A friend of mine has had two fail over a period of several years.

[Abui]

I'll take a stab. Your brakes have worn through the rim until the rim was too thin to support your weight. Always check your rims for wear, if in doubt replace them.

[PacMan]

I'd have to agree and say it was because of the spokes. Light--sure. Strong--not so much.

My LBS mechanic told me if you laced properly tensioned, quality spokes to a piece of tinfoil it would last a lifetime and never go out of true. He was exaggerating of course, but you get the idea.

[mottmcfly]

First off, Glad you are ok enough to even post and hope you're on the mend.

I would like to ask a few questions:

1) What was the actual fall like?
2) Was it a direct result of the rim failure?
3) How old is the wheel set?
4) How much do you weigh?
5) What was the tire pressure?
6) Is there a chance the wheel was not true? I only ask this because with disc brakes it may have been a lot more evident.
7) can we get a better picture from inside the rim? it almost looks like rust where the spokes meet.

thanks,

Mott

[Devoid169]

Wow - I'm riding the same Rolff rims (satellites?) on my GT hard tail (going on 5 plus years now) and do some fairly aggressive riding on them.... Time for a close inspection! To me it looks like a bad extrusion seeing the filure in two different spots. Hope you didn't have too bad a fall. Look on the bright side - now you've got a real good reason to justify the new set of Mavics and an upgrade to disc!! Donny

[RustyIron]

Thanks for all the advice. After further contemplation, I don't think the fatigue was the primary cause of the failure. Perhaps it exacerbated the problem.

Clearly, I should have retired that wheel because of the excessive wear. Six months ago I asked to "mechanics" at the LBS about rim wear, and they shrugged their shoulders and said they didn't know. I should have made the decision based upon my own intuition. I didn't, now I'll always have the question of whether I made things worse by my lack of action.

Personal Lessons Learned:
Trust my intuition. If something looks wonky, don't be such a cheapskate, replace it.

Professional Bike Mechanics:
We customers are dumb and can't figure things out on our own. We depend on you to keep us safe. If something is showing even a little wear, tell us. Then we can make the decision whether to fix it or take our chances.

Adios!