Thorn Cycles Forum
Community => Non-Thorn Related => Topic started by: Andre Jute on February 04, 2013, 07:26:49 pm
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Today I'm in a shop buying a jacket, and the chap helping me turns out to be a roadie, pretty near the beginning of his career as a cyclist I would say.
He's got a horror story. He took in his bike for servicing and on picking it up was told that they had to "fix the rear wheel". He goes out riding, the rear wheel collapses, he slams on the brakes, goes over the bars, and ends up with surgery on his elbow and collar bone. The rim is bent into an S around the join in the rim. There are no obvious collapsed or ripped out spokes. According to him it isn't a wheel with "few spokes" but one with "many spokes".
So what do you think happened here?
Andre Jute
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Andre,
I'd need to know a bit more about the details of the intended wheel service, but here's my hazarded guess:
I've seen such things happen subsequent to a wheel re-tensioning when the residual forces haven't been equalized (i.e. the wheel has not been de-stressed). My guess is his riding -- particularly with application of torque and subsequent loading of the spokes -- caused the wheel to "potato chip". The joint is the break in the rim structure, typically held by pins or a slug. I've seen such "potato-chipped" wheel twist around the joint 'cos it does not have the unbroken integrity of the rest of the rim (unless the joint is welded).
If the rear wheel twisted quickly, it could well have locked between the rear brake pads, primary to his own brake application and all subsequent events.
My postulated cause and effect.
Poor guy, I feel for him and the outcome.
All the best,
Dan.
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Too much tension on the spokes, that's one guess. Wouldn't that make the wheel sort of brittle?
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Thanks, chaps, that's what I thought: an overtensioned wheel, not relieved, the stresses suddenly released, perhaps by a road impact, and the rim twists itself into a pretzel around the join, either because it is the weakest spot or because it is the strongest spot.
Andre Jute
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Dear Andre,
Did he mention who performed the service prior to the wheel's collapse?
Bad bike shops need exposing as much as good LBSs need promoting.
I won't use nearest bike bashers (Bike Pro [!], Kings Heath, Birmingham, UK), not even for the most miscellaneous of sundries, after they utterly Horlicksed my fixie's bb.
Yours, James
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Bad bike shops need exposing as much as good LBSs need promoting.
He's hoping to sue, he says.
If you find a good LBS, let me know. I know one, but he's in Germany...
Andre Jute
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i've looked a million times on utube for a good video on how to tension a wheel never found one.
ok ok i looked maybe 3 times but a million sounds better ;)
local bike shops these days have no intrest in building wheels or even selling light weigh gear, there money is in selling crap to the pilgrim that knows nothing about bikes.IMHO
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i've looked a million times on utube for a good video on how to tension a wheel never found one.
I think you may be talking about stress-relieving (http://sheldonbrown.com/brandt/stress-relieving.html). More details here (http://sheldonbrown.com/wheelbuild.html#seating).
Shown using two methods in this video (https://www.youtube.com/watch?v=Zeyr-brECm4).
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If you have strong hands you can relieve the stresses in a newly spoked wheel by grabbing each spoke cross and the one behind it on the other side of the wheel for leverage and squeezing, repeating all the way around the wheel, then turning the wheel over and repeating so that all crosses are relieved approximately the same amount. This method is the one fancied by Jobst Brand in The Bicycle Wheel. (A book I recommend highly for the mathematically minded but be aware that, unless you can confidently find your way around an engineering text, you may find some of it baffling and much of it infuriatingly dense and brief; Jobst, a very bright fellow, went through life assuming everyone else was as clever and had the same educational advantages, so his instructions are not expansive. Everything Jobst advises in a practical sense is already on the Sheldon Brown site, referenced above by Il Padrone, in a more accessible way; their hearts beat as one on bicycle engineering.)
My hands are strong (a writer is a sort of manual worker -- he operates a keyboard, around 6m flexes a year...) but my skin is soft so what I prefer is...
The Sheldon method: Use an automobile tyre iron. Lay the wheel flat, insert the tire iron over the spoke cross you want to relieve and behind the one next (one cluster of spokes over on the same side of the wheel, and give it a good little downwards jerk rather than a slow press.
It really helps if you can see someone who can build a good wheel do it.
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If you have lots of time, and your wheel isn't stupid-light and therefore dangerous except when perfectly stressed, you can build the wheel, fit it, ride it on a roughish road, and back home retrue, repeating until the truing required is minimal. In short, you can, with the traditional wheel with its huge margins, let the road stress-relieve your spokes, if you retrue after every ride for a while.
I did that with a set of badly built wheels that came on a Gazelle at a time of high stress in my life and found it very relaxing to sit on a low bridge wall out in the country with my nipple spanner, tuning my wheels over many days until they were perfect. You don't have to be a genius to grasp that the forks on your bike are good truing stands if you add a couple of pegs off your wife's washing line and some strips of stiff cardboard or plastic cut from a butter tub or a cold drink bottle.
But, of course, one needs to know that it needs to be done, as the fellow about whose accident this thread is did not, and the wheels had better not be stupid-light to start with, if you're going to let the road act as the stress reliever.
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Flip hope that doesn't put him off cycling :(
Ditto incompetent bike shop...that's why I avoid Halford's like the plague. A few very good mechanics there and some whackjobs but which one lies hands on your bike...?
Good that we have many good bike shops in Belfast, guess the bad ones go out of business fast as there isn't a big cycling culture, so the people that cycle are in the know and shops do it out of love too, not just money.
Still to learn how to tension a wheel, I think I will build one for the old ciocc 78 frame. It looks like both a slow and careful job, and a satisfying one. Bit like knitting a sweater possible. One you can ride on :)
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If you want a good wheel building manual I thoroughly recommend Roger Musson's wheel building book.
It demystifies wheelbuilding and is written for the competent home mechanic in the real world, no engineering phd required.
It shows you how to make all the tools required except a spoke key.
It's only £9 :o and you can get it online NOW as a pdf ;D http://www.wheelpro.co.uk/wheelbuilding/book.php
I can't tell you how pleased I was to have found this. Very very very good indeed.
Yes Jawine, it is very satisfying indeed and lacing spokes is a bit like knitting, but stress relieving is more like cracking walnuts by hand ;D
Ian
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Relieving spoke tension: Lube the nipples and spoke threads so they don't bind up. Put the wheel on the floor and hit the spokes with a rubber mallet. I've even heard of old wheelbuilders placing a wheel on the floor and walking around the rim.
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If you want a good wheel building manual I thoroughly recommend Roger Musson's wheel building book.
It demystifies wheelbuilding and is written for the competent home mechanic in the real world, no engineering phd required.
It shows you how to make all the tools required except a spoke key.
It's only £9 :o and you can get it online NOW as a pdf ;D http://www.wheelpro.co.uk/wheelbuilding/book.php
I can't tell you how pleased I was to have found this. Very very very good indeed.
Yes Jawine, it is very satisfying indeed and lacing spokes is a bit like knitting, but stress relieving is more like cracking walnuts by hand ;D
Ian
is it possible to buy just the book from him seems only a online book is available.
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Anto, download and print it yerself ;D All the other wheel build books are around forty quid so it's still a bargain. No postage to Ireland either :D
Roger very nicely explains why badly built wheels ping, creak and detension themselves on the first ride: and why yours don't have to do that....
Not magic
Ian
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Cheers Ian yip might just do that and he has video instructions on there as well big help to me as i'm the worst reader ever. ;D ;D
thanks Ian.
anto.
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Anto! You read all this waffle ::)
The thing is the book is really clear and simple so it doesn't take a lot to digest.
Monkey see, monkey do. :) (as long as monkey is painstaking and thorough).
Happy reading
Ian
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;D ;D true enough ian. ;)