Your theories on why spokes break.

[tri boy]

Broke a spoke on the Scrambler today. (rear 17" wheel), and although it used to be a common thing years back, with so many laced wheels about, I got to wondering way such short stout spokes on a 17" wheel would suffer such a failure.
They are not long thin types like on 21" wheels. And are only 10000km old. Corrosion isn't an issue, and they are checked regularly for tightness.(maybe it was too tight).
1. Just a random failure? (although I have heard of other new Bonnies doing the same).

2. Poor quality? (maybe, but I would expect early failure in that case).

3. High load while surrounding components cold. (I did "give it some" after refitting the wheel to settle the chain prior to chain slack check).

Its a minor breakage, but the failure is intriguing.
The spoke "popped" its head near the Hub hole.

[Conquiztador]

Broke a spoke on the Scrambler today. (rear 17" wheel), and although it used to be a common thing years back, with so many laced wheels about, I got to wondering way such short stout spokes on a 17" wheel would suffer such a failure.
They are not long thin types like on 21" wheels. And are only 10000km old. Corrosion isn't an issue, and they are checked regularly for tightness.(maybe it was too tight).
1. Just a random failure? (although I have heard of other new Bonnies doing the same).

2. Poor quality? (maybe, but I would expect early failure in that case).

3. High load while surrounding components cold. (I did "give it some" after refitting the wheel to settle the chain prior to chain slack check).

Its a minor breakage, but the failure is intriguing.
The spoke "popped" its head near the Hub hole.

There is two ways of getting a thread on to the spoke: Cutting it and rolling it.

When cutting it you will take away material and the 7 gauge spoke becomes in real a 8 or 9 gauge. When rolling the thread on there is no material taken off, the thread is pushed in to the spoke and the material is squeezed out to make the thread. The rolling is the much better way. But the cutting is the faster way...

If your spokes are chromed and not heat treated then they will snap very easily. (Heat treating: in household oven for 30 minutes on 200 degrees C) I did a bend test with a heat treated and non treated chromed spoke. The treated one would take approx 8 bendings but the non-treated only two bendings before snapping...

If you have non-chromed spokes (or properly heat treated) and roll on thread and they brake early, then you might have an un-eaven tightness on spokes. This is common if the rim is not true and it has been compensated by pulling the rim straight with tightening the spokes.

Common option on Harleys that have been stroked, and will rip spokes, is to fit heavier gauge spokes.

EDIT: One more thing: Good quality spokes when older and heaps of hard use will commonly break at the 90 degree bend in the hub, not at the nipple. If your spokes are not 90 degree but 45 degree or even straight, then they become even stronger.

[merv]

2. Poor quality? (maybe, but I would expect early failure in that case).

Its a minor breakage, but the failure is intriguing.
The spoke "popped" its head near the Hub hole.

You've answered it yourself - option 2 - for the head to pop off the quality just aint flash. With that and your rusty rims you haven't given me any confidence in the product.

[tri boy]

I think you may be right Merv. Had a look at the fracture area of the spoke, and I think the quality of the metal is suspect. (a bit powdery looking).
its been years since I laced wheels but I remember a simple grinding check, showing the sparks was a good indication of the quality of the spoke metal.
(Bright sparks=Good?)
Will try it tomorrow.
Ahh well, these things happen.

Quick measure of the spoke. 5mm thick at the hub end, and only 120mm long. That should be a bloody strong spoke.

[Motu]

Well theoretically spokes work in tension,so it doesn't matter how long or short it is.But if it moves from tension to compression as it rotates,then you have stress reversal....and yes it will break.Which means it's incorrectly adjusted.

But hey - in the real world how many wheels do you see with spoke tension completely out of whack.Come and see my bikes if you need a visual demonstration.For such a weak looking design they can sure take some abuse and still do the job.....and that's why they are still used on dirt bikes.

The modern bike is not designed with a slide rule and a thumb as back up.....the computer knows just how strong it needs to be these days.I reckon your tough looking Triumph spoke is no such thing.

[Max Preload]

I think you may be right Merv. Had a look at the fracture area of the spoke, and I think the quality of the metal is suspect. (a bit powdery looking).

You mean like speckles on the break? Sounds like a brittle fracture - possibly from lack of normalising/annealing after cold working. Goes well with the shitty corrosion protection on the rims I've been hearing so much about.

[tri boy]

You mean like speckles on the break? Sounds like a brittle fracture - possibly from lack of normalising/annealing after cold working. Goes well with the shitty corrosion protection on the rims I've been hearing so much about.


Yep. Looks just like that.:yes:
To be fair, 99% of my drama's with the Scrambler has been based around the wheel assy's.
Should have the new one and another, (replacing an inner, and outer) by Thurs, so I should be rolling for the WWW ride. If more of them start to fail, then I'll chat to Triumph.
Character was liberally splashed around this bike during construction:laugh:.
But besides it's faults, I'm honestly enjoying it.:scooter:
And if I wanted a boringly reliable, uninspired scoot, I would have walked through an Honda Dealership's front door.:dodge:

[Bonez]

Yep. Looks just like that.:yes:
To be fair, 99% of my drama's with the Scrambler has been based around the wheel assy's.
Should have the new one and another, (replacing an inner, and outer) by Thurs, so I should be rolling for the WWW ride. If more of them start to fail, then I'll chat to Triumph.
Character was liberally splashed around this bike during construction:laugh:.
But besides it's faults, I'm honestly enjoying it.:scooter:
And if I wanted a boringly reliable, uninspired scoot, I would have walked through an Honda Dealership's front door.:dodge:I knew you'd throw that in ;) If Triumph need reminding on how long spokes should last they're quite welcome to have a gander at my 550f or the GBs ones :innocent:

Have a good ride home on Sunday?

[Motu]

If Triumph need reminding on how long spokes should last they're quite welcome to have a gander at my 550f or the GBs ones :innocent:


Or they could check out some perfectly good spokes they made over 50 years ago.

[merv]

Or they could check out some perfectly good spokes they made over 50 years ago.

Exactly :whistle::gob:

[tri boy]

Broken spoke replaced, wheel back in, and ready for the WWW ride.:woohoo:
Should I open a betting book to see how long it takes till the next one goes "ping"?<_<
At $8.50 a spoke, I hope its rare.:doh: Works out to be about $300 a wheel.:shit:

[Conquiztador]

Broken spoke replaced, wheel back in, and ready for the WWW ride.:woohoo:
Should I open a betting book to see how long it takes till the next one goes "ping"?<_<
At $8.50 a spoke, I hope its rare.:doh: Works out to be about $300 a wheel.:shit:

In the days I used to do wheels I charged $2.50/spoke nickle plated. Custom made to fit your wheel. Chromed or SS $3.50. $50 to respoke wheel + spokes. 10 years ago now. But can't see the inflation having had that much of an effect.

[McJim]

I remember folks having problems with spokes snapping regardless of quality. The culprit was the hub where the holes for the spokes have worn causing play in the spoke - as Moto pointed out the spoke experiences compression/tension in quick siccession - if there's some play it'll snap the head off the spoke.

Of course my memories are from pushies but the principle is the same.

[Conquiztador]

I remember folks having problems with spokes snapping regardless of quality. The culprit was the hub where the holes for the spokes have worn causing play in the spoke - as Moto pointed out the spoke experiences compression/tension in quick siccession - if there's some play it'll snap the head off the spoke.

Of course my memories are from pushies but the principle is the same.

U are right. But where they brake is at the bend in the hub, not at the nipple.

[tri boy]

U are right. But where they brake is at the bend in the hub, not at the nipple.

Would that therefore mean BMW has got the ultimate spoke now? (those straight ones fitted on their big RGS's).
Or is there still a good engineering principle to use the bent ones. (some form of lateral shock absorption maybe).

[Conquiztador]

Would that therefore mean BMW has got the ultimate spoke now? (those straight ones fitted on their big RGS's).
Or is there still a good engineering principle to use the bent ones. (some form of lateral shock absorption maybe).

Straight spokes are phucking hard to tighten!! They just keep on spinning when the nipple is turned. You end up grabbing them with a set of polygrips or similar. Butted spokes is the go where they are 90 or 45 degree bend. (Butted = thicker gauge at the bended end)

But yes, as long as the spokes are of good quality then the straight ones are hard to brake.

Also, replacing a broken spoke in a wheel with straight ones is a breeze. No need to take any of the others off. If you have a broken one in a wheel with bent ones and the spoke is going to the inside you end up taking a few others off to get it in. Added work!!

[tri boy]

Straight spokes are phucking hard to tighten!! They just keep on spinning when the nipple is turned.

Ahh haa, that will explain why the new GS's have a torx type head at the hub end of the spoke.
Thanks for the info. Ya learn something new each day.:cool:

[limbimtimwim]

This isn't really related, but this is a timely in my case.

Guy at work parks his cheap push bike for a year, gets back on it last week and.. All the spokes on the back wheel snap in the middle. Each spoke had got a scratch from something and corroded right into the middle.

Another guy at work got a cheap small BMX for his son, and he decides to show his son who to do wheelies. First wheelie; all the spokes on the back wheel break.

His son found this hilarious.

[Paul in NZ]

Or they could check out some perfectly good spokes they made over 50 years ago.

From MY experience only, back in the day - all makers at one time or other had 'issues' with spokes....... Usually if they introduced a new ub or re used an old hub on a bigger model or something...

Since we are discussing Triumph spokes.... In the 50's and 60's Triumph always had a pretty low tech approach to wheels. Hubs were simple cast iron / steel affairs and it was BSA and AMC that went with the lighter alloy full width hubs etc. The bigger brakes and full width hubs others used meant shorter spokes and stronger wheels. (remembering tyre technology was pretty bloody basic too)

Triumph never really had many issues with front wheels - probably because their forks were so spindly and their brakes so megre that little strain was placed on the wheel. The later 2LS wheel is very strong. Triumph were late comers to swinging arm rear suspension as well. Their sprung hub was not much chop as suspension but it's width and diameter did make for a bloody strong wheel (I still have nightmares about lacing up a 16" alloy rim to a polished sprung hub using stainless spokes without scratching anything)

Triumphs weakness was rear wheels....

Triumph made 2 basic types of rear hubs (forgetting the smaller bikes and odd balls). The std bolt up design and the QD hub (for 'quickly detachable'). The QD hub was made up of a spool hub with a spline that slotted into the brake hub (brake hub had it's own bearing) so the wheel could be removed without disturbing the chain or brake. The bolt up hub was similar except there was no 3rd bearing or spline - the brake attached to the spool hub with 6 (I think - or 8) bolts)

The spool hub means the spokes were mounted inboard of the brake and were thus fairly long and terminated on a narrow hub. This lead to a comparitively weak structure - especially when modern tyres appeared - more sideforce often broke the spokes.

Triumphs always used a 'waisted' or butted spoke (thicker at the hub end) and it was not uncommon to find busted spokes in the rear which if you had a bolted up hub usually meant a bit of a mission as they usually broke on the brake side - if you look at my bike - I fitted thicker stainless spokes 17 years ago - no problems since.

BSA QA hubs were better because they had the crinkle hub spool and allowed straight spokes which seemed stroger in rough service (like a dirt bike)

Lots of info on the web on all this..

http://www.central-wheel.co.uk/cwc/spoke_details/spoke_details.html

Later bikes with disks have similar challanges but the hubs are wider and stronger and the engineering better understood. All makers have had issues - I remember Suzuki TS400 Apaches shaking their rear wheels to bits...

[SPman]

Any spoke will break, given enough incentive..............

[Motu]

BSA QA hubs were better because they had the crinkle hub spool and allowed straight spokes which seemed stroger in rough service (like a dirt bike)


The BSA QD and 8'' front brake (the steel one with the 6 frost plugs) were the best wheels around,real strogy they were.I had an 18'' and 19'' rear and 19'' and 21'' front so I could swap things around on my old BSA.QD wheels were great,you didn't even need a stand - just lay the bike on it's left side,pull the axle and lift the wheel out,then set the bike upright again,maybe propped up with a rock.30 secs max to remove a wheel.One day the Japanese will reinvent the QD hub and be praised as sooooo inventive.

[motorbyclist]

on my dirtbike i've managed to break 3 spokes in one bang, and kept riding unaware for 3 hours before finding that i couldn't roll my bike backwards - one of the spokes had wrapped itself around the hub and was interfering with the sprocket

rear rim hasn't been quite straight since:doh:

[cynna]

anyone know where to get a broken spoke fixed in chch? was going to get a new tire at cycletreads tomorrow so will give them a ring later so see if they can. failing that any other suggestions will be appreciated

just noticed a broken one at the hub when cleaning my bike....

[Ixion]

on my dirtbike i've managed to break 3 spokes in one bang, and kept riding unaware for 3 hours before finding that i couldn't roll my bike backwards - one of the spokes had wrapped itself around the hub and was interfering with the sprocket

rear rim hasn't been quite straight since:doh:

3 ! Pah, Petal on one notable journey managed to break 24 spokes in the rear wheel! And still made it home. Mind you it took all my effort just to contain her with a single lane, in a straight line. 6 inches of lateral movement at the wheel rim. As to why? Who knows. But I do know that once a couple go the rest start coming out in sympathy real fast.

[Kickaha]

anyone know where to get a broken spoke fixed in chch? was going to get a new tire at cycletreads tomorrow so will give them a ring later so see if they can. failing that any other suggestions will be appreciated

just noticed a broken one at the hub when cleaning my bike....


Wheel Building Services 71 Buchan Street, Grey coloured building, bastard to find
ph 366 4706

[Motu]

As to why? .

The fleet of 25 FA50 rentals I used to look after were always breaking rear spokes.The bikes had a weight limit,but it was never observed....lots of overweight people on them wrecked the spokes real fast.As to why Petal did in those spokes?......:whistle:

[cynna]

Wheel Building Services 71 Buchan Street, Grey coloured building, bastard to find
ph 366 4706

thanks for that. now just have to get the wheel off and get it there