Breaking Spokes

[Bos]

All bikes of reasonable quality have stainless steel spokes and only the cheapest have galvanised steel spokes.

This is what annoyed me the most about my wifes bike. This was a Fuji Sunfire' date=' not a department store special. I still have the wheels and the remaining spokes are so brittle i can snap them using the fingers on one hand.

According to the official specs the spokes were meant to be stainless, but who knows.
[/quote']

 

I know the spoke you're talking about. They're high galvanised high carbon steel spokes that perform very, very poorly. The surface is rough and they're brittle as hell.

 

Here's a photo of such a spoke. It broke, like you say, like glass.

 

Good spokes are made from ductile, degassed stainless steel and don't break like that but in one smooth cut.

 

 

Johan can see this with the naked eye

thats why I dont doubt his judgement

[VTSKING]

 

?

 

Johan can see this with the naked eye

 

thats why I dont doubt his judgement

 

 

 

Some say ... the very ribs of his forefathers were used as spokes for todays top-end wheels ... we simply call him JB!!

[Johan Bornman]

Hmm' date=' I find the discussion quite interesting.

 

Last time I had my wheels trued, the shop told me they only used a spoke tension meter (or something similar, I cant remember the exact word) which ensured all the spokes were tensioned correctly, - I was quite surprised because I wondered how it could work, although I never had the time to ask.

 

It seemed like a bit of hocus pokus to me, but I wondered if there is any merit in having your wheels trued and the spokes checked with this method Johan? - dos it even work.?

 

[/quote']

 

Porky, lets talk tension.

 

Rims out of the factory are never round. They're slightly ovalised by up to 4mm. Right now I have measured a Zip 404 rim and it is 1mm out - 528mm north to south, 527 east to west. This is the best rim I've measured this year.

 

This means, that a wheel that's true cannot have even tension in all spokes or conversely, a wheel with exactly the same tension in all the spokes, cannot be true.  You can't have your cake and eat it.

 

Further, the fact that they've used a tensiometer to do something to your wheel is neither here nor there. They have no idea what that tensiometer told them. If one spoke was 1kg less that the others? what then? Tighten it? Oops, now the wheel is out of ture. I think you get the picture.

 

Onto tensiometers. They measure spoke tension but the measurement itself is arbritary and can only be experimentally determined. For a 32-spoke wheel with standard rim, it is the point where the spokes are just-just not tight enough to collapse the wheel. Depending on the rim's weight (and thus strength), it could be higher or lower.

 

Some wheel manufacturers have determined the maximum tensions for their rim and they publish that - if you're lucky. Some of the ranges they publish are so wide that I wonder why bother? Other wheel manufacturers don't publish the data. So what now?

 

If you build a bastard wheel from scratch, you have no way of knowing what the optimum tension should be other than from experience or by determining it experimentally. Eventually you get a feel and understand the range.

 

it is a myth that too much tension pulls the spokes out of the rim. I have plenty of examples of wheels involved in car accidents and the nipple or the spoke broke but the rim held up. A new rim is far stronger than either the spoke or the nipple. A wheelbuilder will tell you that if you tension the spoke too much, either the spoke or the nipple breaks without any ill effect.

 

Also, when we stress relieve the wheel, we increase the tension to way beyond the supposed maximum of the rim and nothing happens.

 

Here's an example.

 

 

 

 

Rim do however break, we've all seen that. Here's an example of a rim that failed around the spoke holes.

 

 

 

 

 

What happened here is one or more of the following:

 

1) The rim material was chosen to be strong, rather than ductile, so that the rim can be be made lighter by using less material. This alloy of aluminium doesn't perform well under cyclical stresses.

 

2) The rim is heavily anodised - I've gone through this a million times here and by now you all know the story off by heart. This rim was anodised.

 

3) The rim profile doesn't minimise the formation of a bend bubble with each cycle. Compare a Stans rim to this Bontrager with the paired spokes pictured here and you'll see the difference.

 

4) The rim doesn't have reinforcing sockets and or eyelets.

 

 

Now, it is true that working close to its yield point, a metal will fatigue quicker than one experiencing cyclical stresses way below its yield point. That holds true for rims - if the spoke tension is too high for the rim to start off with, it will fatigue quicker and crack. Hence the manufacturers of lightweight rims ask wheelbuilders to limit the tension. This is counter-productive and not very effective, as it only lenghthens the life of a fragile product by a small percentage. With that comes wheels that go out of true, spokes that break etc.

 

 

In summary, there is no merit in the mechanic using a tensionmeter to true our wheels. It adds nothing to the process but tends to justify the bill.

 

Johan Bornman2009-05-12 03:46:46

[andrewc]

Johan,

 

 

 

Firstly, thanks for the enlightening discussion. It really helps (laymen like me) to have the voodoo taken out of these technical discussions!

 

 

 

I have been mulling over the possibility of replacing the wheels on my road bicycle, but I have found the discussions around the various brands and models to be in largely two camps - either "I love these wheels and would buy them again" or "They're rubbish - the spokes keep breaking/the hubs seize/[insert issue here]". And this for the exact same product.

 

 

 

Excluding the obvious issue of mechanical damage to the spokes or riding through potholes, these widely differing opinions are worrying - especially when there is no access to a "try before you purchase" facility - and the costs of these wheels run into many thousands of Rands!

 

 

 

A case in point would be the Shimano WHR560 wheels which seem to be sold quite often here on the Hub - or the Mavic Aksium wheels. The opinions on these wheels are so diametrically opposed "in the wild" (at least in my reading).

 

 

 

Which qualities/features should a person look for when buying wheels?

 

 

 

+ Stainless steel spokes (double butted?)

 

+ Rim eyelets

 

+ Colour anodising (black/gold/red vs plain silver) (detrimental to overall rim strength?)

 

+ ?

 

 

 

From your discussion I gather that, given the correct manufacturing process, flat spokes should be as strong as straight spokes. So this should not be an issue when selecting the wheel (and its components).

 

 

 

Being a larger person (105kgs, give or take a hamburger), the issue of spoke breakage is close to my heart, as I'd hate to upgrade to a lighter/stiffer wheel and sacrifice reliability and safety in the process.

 

 

 

Thanks for (any and all) input on this topic.

 

 

 

Cheers,

 

 

 

Andrew

 

 

 

andrewc2009-05-12 04:08:24

[Johan Bornman]

 

Cut cut cut

 

Excluding the obvious issue of mechanical damage to the spokes or riding through potholes' date='

 

cut cut cut

 

[/quote']

 

Firstly, spokes are not damaged fom riding through potholes. At the moment of impact the tension in the bottom few spokes is temporarily decreased. The tension goes back to normal as those spokes roll over the obstacle. As far as the spokes go, it is a standard cycle and no damage is done. This is a common misconception and you'll always see people here who tell us they give their wheels hell because they ride rough roads.

 

Wheels deteriorate far more from load weight than terrain.

 

 

Which qualities/features should a person look for when buying wheels?

+ Stainless steel spokes (double butted?)
+ Rim eyelets
+ Colour anodising (black/gold/red vs plain silver) (detrimental to overall rim strength?)
+ ?

From your discussion I gather that' date=' given the correct manufacturing process, flat spokes should be as strong as straight spokes. So this should not be an issue when selecting the wheel (and its components).

Being a larger person (105kgs, give or take a hamburger), the issue of spoke breakage is close to my heart, as I'd hate to upgrade to a lighter/stiffer wheel and sacrifice reliability and safety in the process.

Thanks for (any and all) input on this topic.

Cheers,

Andrew

[/quote']

 

As a heavy guy, you should look for the following.

 

1) Double butted spokes.

2) Rims that weight in the region of 500 grams each. Weight is directly related to how much aluminium is in there and you want lots.

3) Double eyelets or to use their right name, sockets.

4) Box section rim such as Mavic Open Pro or equivalent.

5) No anodising or light cosmetic anodising - silver is best. Your choices here are very, very limited....to zero. I don't know of a painted rim that fits this description.

6) Handbuilt wheel or Easton EA 70 or higher.

 

You are right about flat spokes. They can actually endure more stress cycles than round spokes to a factor of 10, according to SAPIM.

 

 

 

 

[javadude]

Johan, what do you think of the Ambrosio Excellight's? They have double eyelets, are box section but a little lighter than 500g.

[andrewc]

Johan,

 

 

 

Thank you. This is very useful as a "buyers guide" for me. In short, I think I'll have to forego the "cheaper" upgrades for now and wait until I can afford wheels that offer better dynamics and will be able to last the pounding my body will give them (the body could also do with some trimming in the interim - with the heavier wheels).

 

 

 

Seriously, thanks!

 

 

 

Cheers,

 

 

 

Andrewandrewc2009-05-12 04:41:51

[Johan Bornman]

Johan' date=' what do you think of the Ambrosio Excellight's? They have double eyelets, are box section but a little lighter than 500g. [/quote']

Nice rims, but who sells them locally? I've only seen them on OEM wheels.

 

 

[dollar]

No Big H - I was having a "discussion" (and some fun ) but I will hou my bek now as instructed What do I know about bicycles?

[javadude]

 

Johan' date=' what do you think of the Ambrosio Excellight's? They have double eyelets, are box section but a little lighter than 500g. [/quote']

Nice rims, but who sells them locally? I've only seen them on OEM wheels.

 

 

 

They are listed on Queen's website(www.queens.co.za). I've got some 36 hole record hubs and thought the Excellights' would be a good match.

 

[dollar]

Gee - what happened? I was learning lots from this thread, then it just died? Promise I wont say anything. Just read!

[wannabearacer]

thanks for all the advice guys im off to an LBS to see what they say...off topic but not really...any great LBS in DBN?? ive heard Shaun power cycles is good...im new to dbn so dont know the local shops yet