Spoke fatigue & wheel rebuilding

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Robin78
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Joined: 13 Nov 2016, 6:55pm

Spoke fatigue & wheel rebuilding

Post by Robin78 »

Hi,

I am replacing both the rims on the wheels on my Specialized Sirrus hybrid bike. The bike is about six years old and the current rims are wearing thin from contact with the brake pads. My plan was to take each old wheel off the bike. tape the new rim to the old one and simply transfer the spokes one by one. However, I have found one of the spokes to be broken (on the back wheel) and now I am wondering if I should also replace all the spokes too. So what I want to know is whether spokes are parts that need to be replaced after a good period of use, or whether they 'go on forever' and I could get away with simply replacing the broken one(s).

Thank you in advance :)

Robin
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cycleruk
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Location: Lancashire

Re: Wheel rebuild - should I replace the spokes?

Post by cycleruk »

I've re-used old spokes on most of the wheels I have built or rim changed.
Yes I have had a few broken ones over the years.
Front wheels I would definitely reuse the old spokes. The rear I would suggest looking at each spoke for damage. The non-drive side will have had less strain than the drive-side spokes.
You'll never know if you don't try it.
Robin78
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Joined: 13 Nov 2016, 6:55pm

Re: Wheel rebuild - should I replace the spokes?

Post by Robin78 »

Thank you - that is very useful.

Robin
fatboy
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Joined: 5 Jan 2007, 1:32pm
Location: North Hertfordshire

Re: Wheel rebuild - should I replace the spokes?

Post by fatboy »

No issues with doing this, I've done it often. I'm a bit sceptical about the non drive side having less strain etc as I have found the opposite with more non drive side spokes breaking. These are on wheels made with plain gauge on both sides which I think means that the nds goes slack and then tight a little bit every time causing fatigue.
"Marriage is a wonderful invention; but then again so is the bicycle puncture repair kit." - Billy Connolly
gxaustin
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Joined: 23 Sep 2015, 12:07pm

Re: Wheel rebuild - should I replace the spokes?

Post by gxaustin »

Check the drive side spokes for chain damage too - and swap out any affected.
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Phil_Chadwick
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Re: Wheel rebuild - should I replace the spokes?

Post by Phil_Chadwick »

I would say that it depends what the old spokes are.

I would always use decent quality spokes, DB on the drive side at least, and on both sides on the front wheel.

If the original spokes are of arbitrary quality then it's probably worth changing them. Relacing the wheel is less faff than the subsequent truing and tensioning
Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Wheel rebuild - should I replace the spokes?

Post by Brucey »

Robin78 wrote:Hi,

I am replacing both the rims on the wheels on my Specialized Sirrus hybrid bike. The bike is about six years old and the current rims are wearing thin from contact with the brake pads. My plan was to take each old wheel off the bike. tape the new rim to the old one and simply transfer the spokes one by one. However, I have found one of the spokes to be broken (on the back wheel) and now I am wondering if I should also replace all the spokes too. So what I want to know is whether spokes are parts that need to be replaced after a good period of use, or whether they 'go on forever' and I could get away with simply replacing the broken one(s).


1) as a rule of thumb if you have broken any given number of spokes to date, other spokes in the same wheel will already be cracked by fatigue and for these spokes, the die is already cast; they will break, it is just a question of 'when'. The number of spokes that are already so damaged appears to be roughly equal to the number that have already broken.

2) The most usual cause of broken spokes is (given a minimal level of spoke quality and fit into the hub/rim) that the wheel has not been stress-relieved when it was built. If you have a used wheel (that has not yet broken any spokes) and you decide to stress-relieve it, you would be very unlucky to break more than one or two more spokes subsequently.

So -with one or two caveats- I'd re-use spokes quite happily.

3) Before getting too excited about rebuilding the wheels from a Sirrus, do check that

a) you can buy rims with the same drilling and
b) that said rims actually have the same ERD

IIRC sirrus models are often supplied with wheels that use weird rims that are very difficult to source.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
yostumpy
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Joined: 29 Oct 2010, 6:56pm

Re: Wheel rebuild - should I replace the spokes?

Post by yostumpy »

So what is the best way of stress relieving the wheels then. I usually take a wooden handled hammer, place the handle between 2 spokes where they cross, (rim side of the cross, ), then with one hand on either end of the hammer, push it downwards towards the axle, until the spokes flex. Is this correct.
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531colin
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Re: Wheel rebuild - should I replace the spokes?

Post by 531colin »

I simply followed Brandt, and stress-relieve by grasping and squeezing near-parallel pairs of spokes.
You will need considerable protection for your hands, I find 2 pairs of hide gloves better than one pair.
I now have some arthritis in my hands, but I can't say its any more than could be expected in somebody of my age. Building the odd pair of wheels I don't think will do any harm, but I would be careful building for a couple of days a week....for example, tension with both hands on the spoke key and the wheel in the fixture, don't tension turning the key with just one hand.
Oddly, Brandt mentions "driving the spoke crossings towards the hub using a screwdriver handle" before the wheel is tensioned, but (uncharacteristically) doesn't say why.....I never did it.
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Phil_Chadwick
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Re: Wheel rebuild - should I replace the spokes?

Post by Phil_Chadwick »

I use a screwdriver shaft, inserted above the crossing-point between spokes and pushed down to force them apart, then inserted below the crossing point and pulled up to force them the other way. Works well, and it's easy on the hands - and fast.
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NATURAL ANKLING
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Location: English Riviera

Re: Wheel rebuild - should I replace the spokes?

Post by NATURAL ANKLING »

Hi,
I use Brandts method, but like 531colin use plenty hand protection, leather a must, two pairs lighter any gloves under the leather.
I have for some years used hand protection doing any manual work, these-
http://www.ebay.co.uk/itm/190788256074?_trksid=p2057872.m2749.l2649&var=490129197557&ssPageName=STRK%3AMEBIDX%3AIT
http://www.ebay.co.uk/itm/190788256074?_trksid=p2057872.m2749.l2649&var=490129197557&ssPageName=STRK%3AMEBIDX%3AIT
s-l400.jpg (24.36 KiB) Viewed 4928 times

I have 9.5" hand span and wear size 9, they do vary a size or two with different batches / makes.
Protects hands from dried out split fingers, keeps them clean too, I you suffer splits always use some micropore tape on fingers, hand cream does nothing for dry hands.

If spokes aren't tensioned some what before stress relieving then it will tend to bend around points of contact with edge of hub flange and tool you use I would of thought, you are also trying to form spoke head to seat in the flange, lay flat.

Real test after wheel is stress relieved remove one spoke and examine :?:
NA Thinks Just End 2 End Return + Bivvy - Some day Soon I hope
You'll Still Find Me At The Top Of A Hill
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531colin
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Re: Wheel rebuild - should I replace the spokes?

Post by 531colin »

NATURAL ANKLING wrote:.........
If spokes aren't tensioned some what before stress relieving ............:


"stress relieving" ......doesn't this mean making sure that the spokes are bent to the exact angle(s) required in the finished wheel? ie. they are not flexed to achieve that angle? (the flex is the "stress" in the metal that needs to be relieved)
So the wheel needs to be "finished" ie (tight, even, true, round, dished.......) before it can be stress relieved?.....and the stress is relieved by momentarily taking the tension well above that which will be seen in service?
This is one area where I went away from Brandt.....if memory serves, Brandt stress-relieved when spokes were below final tension......I used to do it at final tension.
Brucey
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Re: Wheel rebuild - should I replace the spokes?

Post by Brucey »

I think that if you stress-relieve at a higher starting tension, you can get a greater increase in the spoke tension for any given amount of 'squeeze' , so if nothing else, such stress-relief is easier to do.

However in relation to nipple kinks especially, I think there are some subtle things going on.

The first thing is that if you give a spoke a set (in bending) but then don't stress-relieve afterwards, the spoke will still be chock full of residual stresses from the bending operation. Even if the spoke then sees a simple cyclic tension load (no bending component) then it may still fatigue in the same way as if it were seeing a cyclic bending stress.

Another thing is that Brandt's method (squeezing parallel pairs) will tend to overbend the spokes near the nipple, because the spokes are being forced in a direction where the nipple has already run out of articulation in many cases. Overbending may then result in an in-service cyclic bending stress in the spoke end. Note that this is more likely to happen when the wheel is already vulnerable to this kind of problem.

In mitigation of the above, if the nipple later goes on another turn or so (as it might, should the stress relief be carried out at a starting rather than final tension) then an overbend in the spoke end may no longer be of great detriment because the bent section will be better supported once the nipple is wound on a bit further.

FWIW I have always stress-relieved by squeezing spoke crossings inwards (i.e. in an axial direction) using the heels of my hands. This (I think) greatly reduces the chances of overbending the spokes near the nipples.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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531colin
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Re: Wheel rebuild - should I replace the spokes?

Post by 531colin »

Brucey wrote:................
Another thing is that Brandt's method (squeezing parallel pairs) will tend to overbend the spokes near the nipple, because the spokes are being forced in a direction where the nipple has already run out of articulation in many cases. ..................


No. Squeezing near-parallel pairs of spokes, on the same side of the wheel......
the spokes emerge form either side of the hub....therefore squeezing them together makes the nipples approach radial to the rim, and won't help put a set in the nipple end at all......
isn't it?
Brucey
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Re: Wheel rebuild - should I replace the spokes?

Post by Brucey »

531colin wrote:
Brucey wrote:................
Another thing is that Brandt's method (squeezing parallel pairs) will tend to overbend the spokes near the nipple, because the spokes are being forced in a direction where the nipple has already run out of articulation in many cases. ..................


No. Squeezing near-parallel pairs of spokes, on the same side of the wheel......
the spokes emerge form either side of the hub....therefore squeezing them together makes the nipples approach radial to the rim, and won't help put a set in the nipple end at all......
isn't it?


ah, yes, you are quite right, but this means you might still get an 'underbend' which is just as bad, for similar reasons.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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