Heat in storage room snapping spokes?

[Annoying Twit]

Really? Can this happen?

http://www.trademe.co.nz/sports/cycling ... 952041.htm

[irc]

No. Unless the storage rooom is at several hundred degrees C. THink about it. People tour in desert areas with over 100f temps and in the same tour get below freezing temps in the mountains. Without snapping spokes. How would a few degrees of warmth in a room do it?

Either the seller is full of BS or more charitably has found broken spokes when washing the bike prior to taking pics to sell it.

[Annoying Twit]

No. Unless the storage rooom is at several hundred degrees C. THink about it. People tour in desert areas with over 100f temps and in the same tour get below freezing temps in the mountains. Without snapping spokes. How would a few degrees of warmth in a room do it?

Either the seller is full of BS or more charitably has found broken spokes when washing the bike prior to taking pics to sell it.

That's what I thought. But, look at how many spokes are broken. And they're all broken in the middle. I believe that something very strange has happened to this bike. What?

[PH]

Maybe a heated caretaker with a set of bolt croppers who didn't like the bike parked there.

[Annoying Twit]

Maybe a heated caretaker with a set of bolt croppers who didn't like the bike parked there.

(Actually being serious). Vandalism seems the most likely reason to me.

[531colin]

Super-heated mice. See it all the time.

[thirdcrank]

I've always used places like boiler rooms to store my bike at work etc., and never had a problem with spokes. I would have thought that if there were to be some force which heavily stressed all the spokes in a wheel simultaneously to the extent of causing damage, then the hub flanges might be where it occurred.

[Annoying Twit]

Maybe it was giant weta.

[ferrit worrier]

If anything they will slacken off. As they warm up the metal expands.

the coefficient of expansion for steel , •steel: 0.000012 (m/moC) (taken from t he engineering toolbox http://www.engineeringtoolbox.com/linea ... _1379.html)
as I understand it the object will expand 0.000012 mm per mm, per degree rise in temp. ( Quite willing to be corrected on that)

Malc

Edited to say, the rim will expand of course. but I think it will be in a uniform progression, that is, the rim expands around it's circumference while the spokes expand diametrically.

[pete75]

Probably. Som years ago on a warmish day I put my bike in the car. On the way home I stopped fro an hour or so. Car parked in the sun. When I got back in the car was at a real dog killing temperature. Got in to to drive off and heard a loud ping. When I got home I noticed one of the rear wheel spokes had broken just below the nipple. They were decent wheels which had done about 2500 miles without problems. I'm convinced it was the heat what dun it.

[meic]

The linear thermal coefficient of expansion for aluminium is about double that of steel.
So there is a theoretical means by which the spokes could have their tensions increased.

[Brucey]

due to heat, the tension in the spokes will most likely increase; the reason for this is that the thermal expansion coefficient of Aluminium alloys is usually more than that of stainless steel and it is substantially more than that of non-stainless steels. Thus the rim 'grows' more than the spokes do, so they get tighter.

However this tension increase certainly won't be enough to cause catastrophic failure; if this were likely, spoke breakage in the back of hot cars would be very commonplace. Probably Pete's failed spoke was cracked already, and the tension increase gave it the final push.

By calculation; a 700C rim seeing a +50C temperature increase will increase in diameter by about 0.6mm. The difference between that expansion and that of the spokes will be about 0.1 or 0.2mm (depending on the exact materials used), or about half that per spoke. Whichever way you cut it, the tension increase is unlikely to be more than that comparable to (say) an extra 1/4 turn on each spoke. If you think that is going break stuff by itself then there would have to be something very wrong with the wheels to start with; it needs a helping hand.

I think the true answer to this mystery lies with corrosion, specifically stress corrosion cracking (SCC); the bike is advertised in Auckland, a city entirely surrounded by the sea. If the bike saw any salt spray, and then was placed in very hot, dry storage, the brine would evaporate until it got to the highest strength possible. This kind of brine can easily generate local corrosion cells on otherwise corrosion resistant materials, and wherever the stress is highest, breakages will then occur. If the storage conditions were also slightly acidic then this would also help corrosion once it got going.

That stress has had a role to play seems likely; in the photos all the broken spokes in the front wheel are on the disc side, where they are tightest. Having said that, what is going on with the rear wheel is less clear.

FWIW I have occasionally seen and heard of similar but isolated failures of this kind. I have also seen severe corrosion (in all parts) caused by apparently innocuous salty spray that managed to dry out and increase its strength.

cheers

[Gattonero]

Really? Can this happen?

http://www.trademe.co.nz/sports/cycling ... 952041.htm

What a joke.
In south Italy you would have no wheel left then, when riding in 40ºc!

I'll be more concerned about the tyres perishing.

[Annoying Twit]

The corrosion is an interesting concept. I note that the relative difference between new prices and second hand prices seems bigger in Auckland than it does in the UK. A corrosive atmosphere may explain that. I did notice a number of bikes where alumninum bits, such as derailleurs, looked surprisingly either worn and/or corroded. These were quality components, e.g. tiagra and ultegra bits, too.

I'll see if I can find one ... Look at the rear derailleur on this one: http://www.trademe.co.nz/Browse/Listing ... 1214897511 (You can zoom in by mouse overing the image.) That looked rather odd to me.

[Gattonero]

I lived by the sea, my first good Mtb is now 25yrs old and the Shimano Xt parts are still good, no corrosion even after countless miles and pints of sweat poured onto, and quite a few trips to the sea. And like me, all the other chaps there.
Guess why, everyone looked after their bikes.

This thing about spokes "simply" breaking because of temperature or corrosion is really BS. The hub or rim would fail well before that, and if so it's all screaming "hey, I never bothered about looking after this bike, spokes are breaking. Yeah, let's make it up is due to the heating in the storage room"