[Closed] Wrong gear combination results in broken carbon frame 🙁

I'm lost now, Glupton, your link seems to disagree with you

If the chain is too short, it will be at risk for jamming and possibly ruining the rear derailer if you accidentally shift into the large-large combination. Never run with a chain that is too short, except in an emergency.

If the chain is too long, it will hang slack in the small-small combinations. You should never use those combinations anyway,

I'm with the OP on the frame warranty self-build issue though - A manufacturing defect is just that, regardless of who builds the bike

most components/frames have it, Its to stop people fitting parts incorrectly or ones that are unsuitable. If the parts broke through their intended use then no problems.

If they didn't carbon road frames would weight a tonne to be prepared for people fitting Rockshox Boxxers to handle a few pot holes on the route to work.

George's Link to Sheldon is about set up not use. It's always been wise to set up a chain to cope with big/big - just in case. However, using the extremes has 'always' been frowned on as it puts the chain through a big zig and accelerates wear. How has that changed by using a 34/50?

This doesn't make sense. Using the extremes is usually a sign of someone with zero mechanical sympathy and/or a novice.

How has that changed by using a 34/50

ever tried doing the compact shuffle on a 20% gradiant ? - that is dropping to 34 and trying to get the chain down the block quick enough that your legs dont propel you into a wheelie.

Different if your recreationally riding mind you...... lets be honest - its just like having 1 x 10 twice..... a triple i can buy it creates a big angle..... but on a double the difference is miniscule.

compacts are terrible devices anyway. When i build my own bike instead of using jaynes handmedowns itll have 53:39 on it.

The smaller rings mean a less acute angle too. I know when I go big/big on mine (53-27) it's quite a sharp angle, whilst the newer Madone I rode at the weekend was far happier (50-28).

A few thoughts.

- To me, the damage looks consistent with a chain that's locked up (due to being too short), then driven the mech into the spokes (as it's twisted) and in turn then compressed/bent the chainstay as the rear wheel has tensioned the chain to the point of failure. The forces involved in this sort of thing are really quite high so the snapped stay is no suprise. I've seen very chunky alu frames bent after this sort of mishap.

- Big/big, small/small isn't advisable, recommended or particularly efficient but I find that riders can get very stupid when tired (and this definitely includes me!) and choose bad gear combos hence why bikes should be set up to able to do big/big without expensive mishap!

- Carbon can be repaired and this damage is most likely not too complex to fix by someone like http://www.carboncyclerepairs.co.uk/index.html

- This is not a warranty claim so don't piss off your LBS by claiming it is. By all means ask about what they can do (which would hopefully include a trade + VAT replacement) but don't expect anything free.

Mmmm ok. This has passed me by.

The triple/double comment above is just a red herring. Extreme combos were avoided regardless of how many chain rings there were/are.

Sorry for my continued scepticism, this just sounds like a change to custom and practice due to the disposable nature of, well, everything <sigh>.

do you have 1 x 10/ 1 x 9 on your mtb .

what positions your ring in .... the middle or outer ?

if its the middle i hope you avoid the bottom three cogs....if its the outer i hope you avoid the top 3 😉

Trail rat. The context is road (2x10 though I run 3x9 on tourers/tandems). All my MTB's still run 3x9. Remember, I [i]am[/i] a Luddite 🙂

I have 1x10 but I still wouldn't deliberately use big ring with the two or three biggest sprockets just because it's not particularly efficient - I'd rather shift to the small chainring then and given how well front chainrings shift now, I don't really see the issue. YMMV of course.

1x10 is ok for me because you get some payback for the lack of extra chainrings.

Somebody quoted Sheldon Brown up there ^

I'll see you and raise you....

http://www.sheldonbrown.com/gears.html

"Try to avoid the gears that make the chain cross over at an extreme angle. These "criss-cross" gears are bad for the chain and sprockets. Especially bad is to combine the inside (small) front sprocket with the outside (small) rear sprocket. This noisy, inefficient gear causes the chain to wear out prematurely".

ok so doing the sums

if im approaching the big end of the block in the 50 and drop down to my 34, i then need to drop 6 gears at the back to get the same gear at the same time or i end up being spat out the back on the climb....or spinning like an absolute loon - ive yet to do a race though where ive needed the 34.

the 34:12 is a non issue .... i tend to find im going down a steep hill on the otherside of a steep climb (if its made me drop to a 34 its steep) and ill shift everything while recovering.

if we werent supposed to use 50:25 then why does the front shifter have a trim to allow us to 😉 YMMV but your bike should not explode into shards of carbon like this because you used 50:25 or even 50:28 (with appropriate mech)

if im approaching the big end of the block in the 50 and drop down to my 34, i then need to drop 6 gears at the back at the same time or i end up being spat out the back on the climb....or spinning like an absolute loon.

There is a point at which the change can be a faff, but looking ahead, up the road can help, as can looking at the gears others are riding.

They're your tools, and you know what folk say about blaming them.

I haven't got a gear table to hand but I just don't find that - I usually reach about 4th from the biggest at the back then shift to the 34 on the next change down and up maybe a couple? Three possibly? certainly not 6!

FWIW, surely you're not racing on a 34/50 compact? I'd want closer ratios if I was racing a compact (50).

or do you mean that you're effectively racing on a 1x (because you only ever use the 50)?

but your bike should not explode into shards of carbon like this because you used 50:25 or even 50:28 (with appropriate mech)

Sorry Trail Rat, that did make me smile considering the context of the thread 🙂

Enough, I understand your point about running up and down the block to get the same gear (or presumably the next one up/down) but I don't do that or get spat anywhere as I don't race. I preempt a bit more like Clubber, that's probably why it isn't an issue for me.

It's a strange contradiction, transmissions are supposed now to be much less 'sturdy' than days of yore with 10 and 11 speeds and skinny chains and yet we now advocate using them less sympathetically.

It's a strange contradiction, transmissions are supposed now to be much less 'sturdy' than days of yore

Yeah but that's a myth IMO...

Wah! Two myths busted in one day. Nooooooo........

thats depends wether your looking for the same gear or a gear near what you had and are comfortable with.

my gear tables says its at least 5 gears down the block - maybe 6 depending on what jumps i have , i dont remember when i drop to 34 to get the same.

yep i effectively race 1 x 10 as the compact is the work of the devil. the 34 just feels so labouring - and thats from a spinner.....I have a compact as i dont race much at all on the road and use the hand me downs from the mrs' racing bike - she needs a compact.

I have 53:39 on my good TT bike ;)- its also going to be 1x10 shortly..... no need for the inner ring on that at all.

So what's happening to the OP, I'm not bothered about the arguments about what gears you can can't run, if you have two on the front and then on the back then you can run any combination.

But if I am correct is this a case of the OP buying a frame, putting too short a chain on it, not setting the B tension screw properly, riding it, chain running tight, mech catching cassette, locking wheel, which then transmits force to frame under load and crushes the driveside chainstay?
but shop wont warranty as it's not a manufacturing defect?
OP then wants to reverse the story and say frame broke causing damage.

The OP isnt that well known cyclist Emma Way is it?

Oh and I suppose it's the LBS's fault also

I think people are arguing at cross purposes - big-big isn't good practice, but the bike should be set up to use it.

Using big-big and small-small isn't a great idea* because it means the chainline is far from straight (so the chain rubs on mechs, efficiency is less, etc), and those ratios aren't usually much use anyway.

However, every bike should be built so that big-big can be used because, if the chain is too short, the consequences can be very expensive.

*On recumbents with a much longer chain run, it's not an issue.

I suppose the mech jamming and locking the rear wheel translated in to sudden rather high torque loading of the rear end of the bike...

I have had a similar thing happen to me on an aluminium road frame, simply coasting downhill so just soft pedaling to change gear, then just the loading created by a rear wheel eating a mecha at ~40mph and locking up - knackered the wheel, spangled the mech and bent the replacable hanger, but the frame itself was fine so like you say a ~£20 hanger and all was well again...

Perhaps a Carbon frame would not have survived this, perhaps the lack of a sacrifical mech hanger did make the situation worse for the OP? hard to really estimate...

It's not so much an issue of frame-snapping ultra-torque applied at the pedals as some of you seem to think, but forwards inertia of bike + rider(~100kg @ ~20+ mph?) very suddenly being converted to rear wheel/triangle mangling, laterally applied torque @ ~90degrees to the direction of travel...

I'd give some serious thought to doing the repair, apparently you have no warrantee anyway so what is there to lose? It would be a handy learning exercise IMO.
But take a good look at all the other tubes in case there is other, un-revealed damage to the frame. Especially the other 3 stays and perhaps at the Downtube/BB junction, there might be more repairs required than just the obvious snapped stay...

bencooper - Member
I think people are arguing at cross purposes - big-big isn't good practice, but the bike should be set up to use it.

Using big-big and small-small isn't a great idea* because it means the chainline is far from straight (so the chain rubs on mechs, efficiency is less, etc), and those ratios aren't usually much use anyway.

However, every bike should be built so that big-big can be used because, if the chain is too short, the consequences can be very expensive.

*On recumbents with a much longer chain run, it's not an issue.

100% my view. BTW when does a civilised discussion become an argument? 😉

When the first insult it thrown.

You muppet!

[img] [/img]

.....

It's time to play the music
It's time to light the lights
It's time to meet the Muppets on the Muppet Show tonight

It's time to put on make up
It's time to dress up right
It's time to raise the curtain on the Muppet Show tonight

🙂

I don't think the OPs gear selection matters much at all TBH.

Like he said, he was at the bottom of a hill, just starting to climb, flicked a gear and the failure occurred, I assume therefore he was carrying a bit of speed (inertia) from the preceding flat or descent?

people think in rather linear terms when it comes to bikes as structures, but they are anything but linear, I bet the rear wheel suddenly locking threw the OP forwards/over the bars(?) that's because his body and most of the bike had inertia, the rear wheel being locked had the effect of arresting that rather rapidly.

almost all of that energy was converted into tension/torque applied about the rear axle, the rear wheel in effect becomes a fixed lever, the application of all this loading is offset to one side (Drive) so a proportion of it is translated as if a lateral force were being applied to the wheel (had the drive-side end of the QR jumped out a little in the dropout when you took it out OP?).

So you get a pretty significant tensile loading of the stay (not compression) combined with a high torsional load, you're pulling and twisting it using your body's entire mass and forward speed all at the same time.

The effect on the frame was a bit like trying to land a 6ft double and casing the landing sideways, except on a composite road bike, so funnily enough the stay snapped...

Can you give me that in English now please?

glupton1976 - Member
Can you give me that in English now please?

people think in rather linear terms when it comes to bikes as structures, but they are anything but linear, I bet the rear wheel suddenly locking threw the OP forwards/over the bars(?) that's because his body and most of the bike had inertia, the rear wheel being locked had the effect of arresting that rather rapidly.

Oddly enough I run a very short chain on one road bike and if I attempt through stupidity to put it in the big rings front and back it just wont go.
Fact is with a short chain there is no way the mech can touch the cassette, its stretches it [mech] out horizontally away from the cassette, I could take some pictures to show but cant be arzzed
However a to long chain and the jockey wheel can touch the cassette and wow betide you if you go little rings front and back.
Now just suppose the chainstay snapped first, worth considering IMHO

I appreciate on a stand with no momentum behind it it wont go

now go repeat your fact while climbing a hill with momentum

come back with your new answer.

Nope still wont go

dales rider, you are simply wrong.

it is a problem that is prevented by using the B screw on the Shimano Mechs.
if the chainstay broke first the rider would have felt the frame feel odd but nothing catastrophic as described.

But the OP has already stated that the frame did not break first.
Or you could just re-read the title of the thread.

Sancho - Member

dales rider, you are simply wrong.

Ooops am I must pop and tell my bikes that, oh and I guess OP was watching carefully when it failed but hey ho not my bike and not my problem.
As for how the B screw can alter chain length well I've a lot to learn, in fact I'll go put some links back in my mates chain and tell him you cant stop the jockey wheel touching your cassette because your b screw is turned to the max, you'll just have to put up with it.

I am simply trying to advise that the jockey wheels will contact the cassette when the b screw is not adjusted properly.
It's why the screw is there.
The B screw doesn't alter chain length ( you do that by adding/removing links) it alters the position of the mech, which when you run either a short chain or a larger tooth cassette you adjust to keep the distance of the jockey wheel away from the cassette, if it is not adjusted properly then the jockey wheel will come in to contact with the cassette, it may not happen on your bikes, but I have seen it on many occasions.

But as the OP has described how it all happened then he didnt need to be watching what happened, as I said a frame failure would not have caused all the damage that was described, as I have seen frames fail on chain stays seat stays the frame would have felt wobbly, or soft, but not locking up wheels etc.

If you want to pop in to my shop (crosstrax) I can demonstrate to you how the b screw can help avoid this issue.

Sancho you misunderstand yourself, but with your limited experience I forgive you. Unlikeley to pop in your shop for a screwing course but I will pop in one day and maybe teach you something more complicated you may just be able manage.

Hows life in the ivory arm chair.

dales rider, you are simply wrong.

it's 'woe betide', not 'wow betide'

HTH

Dales rider

I totally understand myself and what Im talking about and have a lot of experience, but I dont see how you can't see this, when the short chain runs big to big it pulls the mech forward, the b screw would stop this, pulling it forward doesnt pull it away from the cassette, in the final movement it pulls it back up and in to the cassette, hence the OPs damaged frame and countless mechs trashed, hence the fitment of the B screw.
I just dont understand why you dont see that.
But again youre welcome to discuss it and point it out to me in the shop over a biscuit and tea

Maybe you could teach me about the software for the Management of Nuclear Fuel Rods in Magnox Reactors, (one of my old jobs before I started fixing bikes about 10 years ago. it was fairly complicated, but hey ho. not my problem anymore.

mickolas - Member

dales rider, you are simply wrong.

it's 'woe betide', not 'wow betide'

HTH

Accept that I'm sh1te at spelling, my grammer school education to blame.

I see what you did there

I could but wont turn a post into a personal slagging match, nuff said Sancho and leave it at that.