Too fat for Campag?

[Tin Pot]

Soooooooo...what you're saying is avoid potholes?

 

[Drago]

Nooooo....what I am saying is that everybody thinks their spokes break because of potholes. It is not that.

Gotcha. Avoid potholes.

 

[Hugh Manatee]

It is a common misconception that potholes and kerb bumps damage wheels in the long run. That's just not true.

Wheels fail in two places - spokes and rims. The spokes fatigue at the elbows and first thread and rims fatigue in a zone around the spoke holes.
The mode for rims and spoke elbows is metal fatigue and the mode for the thread failure is crack initiation. All these modes of failure are exacerbated by a combination of stress cycles and cycle amplitude. In other words, how many times in total has the spoke loaded and unloaded and, how many times in total has the rim relaxed and re-tensioned. The answer is easy - once per wheel revolution. The second part of the combined stress contributor is the amplitude. In other words, how much does the spoke/rim load/unload with each revolution. This is a function of your weight.

In one kilometer your wheel turns 500 times (circumference is approximately 2 meters). In 20 kilometers, an average commute, say, your wheel turns 10 000 times. That's 10 000 stress cycles. In one commute you jump the kerb once and hit a pothole once. The ratio is thus 10 000:2.

Conclusion: Just riding along does more damage than any other activity on your bike.

The reason why your Campag wheels have not broken is because the weight limit is a complete and utter arbitrary limit. It isn't the result of any sort of measurement, nor is it a tipping point for sudden onset of fatigue or failure.

The same amount of fatigue will set in with 10 000 revolutions at an amplitude of 80kg than would with 100 000 revolutions with an amplitude of say, 70kg.

It is the combined effect that matters.

The only time a meaningful weight limit can be put on wheels is when the wheels will flex enough with a rider of X- kilograms so that it touches the fork blades or chainstays or brake blocks. Even then, the style of riding would dictate the rider's weight.

You say you've never damaged any of your components. How do you know that metal fatigue has not started a spoke or rim crack yet?

Oh no. Now I'm going to trying to work out how many times my wheels go round on tonight's ride. If my brain explodes, it'll be your fault.

 

[Disabledcyclist40]

My God, I'd better cut out all snacks then as my cakes weigh 82kg

 

[Gravity Aided]

People tend to forget that racing bikes are designed for racing cyclists, not overweight ex golfers.

Mine seem to get along okay. Might be because I still golf, now and again.

 

[Drago]

I'm heavy enough to have eaten a Golf.

 

[ColinJ]

It is a common misconception that potholes and kerb bumps damage wheels in the long run. That's just not true.

I was thinking more in terms of the very short run, as in - before hitting pothole or kerb, wheel ok; after hitting pothole or kerb, wheel damaged! That definitely does happen - I have witnessed people damaging wheels that way on several occasions.

You say you've never damaged any of your components. How do you know that metal fatigue has not started a spoke or rim crack yet?

I'll rephrase it for you - I am over the arbitrary weight limit, and for years was about 25% over that arbitrary limit. I have ridden tens of thousands of kms on Campagnolo wheels and never broken a spoke or a rim, and have not seen any cracks developing yet. If/when damage finally manifests itself it may be partly due to my weight but as long as the wheel does not suffer a catastrophic failure I will be happy enough - I've had my money's worth out of them. The most likely fate for the wheels appears to be the braking surface on the rims wearing away.

I was given some very poorly built cheapo wheels once which did suffer a few broken spokes. I didn't consider them to be worth the effort sorting out so I scrapped those.

I broke a spoke on a Mavic Aksium rear wheel once. The reason for that was that it was a used wheel from a friend whose rear mech had gone into the spokes and broken a couple, which he replaced, and then he sold me the pair of wheels for £50. What neither of us had noticed was that the carnage had also extended to that third spoke which a post mortem revealed significant damage to.

 

[GrumpyGregry]

Maybe Campag just want skinny pro looking riders using their stuff, they need to maintain their image.

I've screwed that up then.

 

[GrumpyGregry]

It is a common misconception that potholes and kerb bumps damage wheels in the long run. That's just not true.

In one kilometer your wheel turns 500 times (circumference is approximately 2 meters). In 20 kilometers, an average commute, say, your wheel turns 10 000 times. That's 10 000 stress cycles. In one commute you jump the kerb once and hit a pothole once. The ratio is thus 10 000:2.

whilst, using your in the long run get out that is broadly true, hit a pothole or kerb whilst carrying enough kinetic energy and your wheels will enter catastrophic failure mode no?

It is the combined effect that matters.

Nope. Whenever it occurs in a wheels life span it is the amount of force required to cause a catastrophic failure at any given point in time that matters. Brand new wheel, 100 metres in, hit a big enough pot hole hard enough and your done.

 

[Yellow Saddle]

whilst, using your in the long run get out that is broadly true, hit a pothole or kerb whilst carrying enough kinetic energy and your wheels will enter catastrophic failure mode no?


Nope. Whenever it occurs in a wheels life span it is the amount of force required to cause a catastrophic failure at any given point in time that matters. Brand new wheel, 100 metres in, hit a big enough pot hole hard enough and your done.

Of course hitting a pothole that's got sharp enough edge to penetrate the tyre's cushion will dent a rim Who denies that? But that's not what Campagnolo's 82kg limit warns about.

Anyone can trash a brand new wheel 8 meters into the run.

 

[mustang1]

Maybe Campag just want skinny pro looking riders using their stuff, they need to maintain their image.

Yeah a bit like fashion houses which do not make XL size clothes.