Too much power for derailleur?

[dirkbike]

Hey guys, @dirkbike here.

I've tested the Levo in different builds, the Kenevo comp, and now purchased the Kenevo Expert a couple of days ago and really loving the bike, until today... I was powering up a really steep climb that normally only hikers or horses do, bikes are allowed, but unless your mega strong, you're going to be hiking, it's really steep. Which is why I really wanted to see if I could get up it with the new assist bike.

Anyways, I was pedaling a good cadence in full turbo mode, in the granny gear when all of a sudden, the SRAM GX derailleur broke off from pure torque and power alone. It didn't get caught in the spokes, nothing weird. It snapped off, went into the spokes, and smashed into the seat stay. Has anyone experienced this before? Whats the most durable derailleur for e-bikes? I'm going to get it warrantied but certainly don't want it to happen again.

Cheers,
-Dirk

 

[Gary]

when all of a sudden, the SRAM GX derailleur broke off from pure torque and power alone

No it didn't. The torque acts on the top of the sprocket.
The derrailleur just guides the chain to the lower portion of that sprocket. and tensions the chain to stop it flapping.
Something else happened.

 

[dirkbike]

Hmm so what the heck could have happened? I was literally fighting to keep it going pushing as much torque as I could apply in 100% support mode, figured it had to be from too much strain on the drive train, but I can see your point which is, it should go from top dead center of cassette to front chain ring, but at the same time, I can see the torque working it's way down the cassette to the derailleur especially since it doesn't wrap around the cassette like a moto chain, it's only meshing on 1/4 of the cassette, and with the amount of play in the teeth/chain mesh, I'm no scientist but it makes sense in my head the chain wanting to pull on it.

 

[Gary]

in your lowest gear there's a good chance it can touch a spoke and get taken out.. it can also get ripped off if your chain is too short and the suspension compresses or something jams anywhere along the chain causing it to pull the derraileur forwards too far. A seized jockey wheel can cause this too. (SRAM jockeys are bad for this). As can a twisted chain link. or if it had previously been damaged by a hit. there's a rather large list of possibilities. including a manufacuring defect. (unlikely but possible).
is there honestly no other marks on the mech itself or your drive side spokes? and is the bottom jockey wheel spinning freely?

 

[steviedsolve]

Also, on my new Haibike I've had to tighten the hanger mount bolt 4 times since new, because torquey vibration changing gear has a habit of loosening it. Is it still tight? I'd say it got caught in/knocked into the spoke. I went through 3 derailleurs in two weeks this way once to find that the hanger was bent. Swapped that and no issues since.

 

[Kaelidoz]

Never happened to me with my poor altus m-2000. And I do push really hard on those steep climbs.
Either something else happened or this derailleur was faulty.

 

[Gary]

Also, on my new Haibike I've had to tighten the hanger mount bolt 4 times since new, because torquey vibration changing gear has a habit of loosening it. Is it still tight? I'd say it got caught in/knocked into the spoke. I went through 3 derailleurs in two weeks this way once to find that the hanger was bent. Swapped that and no issues since.

Thread lock it. this often happens because of poor tolerances/fit in replacable hanger design as much as torque. vibrations when descending and cornering forces will have more effect on loosening the bolts. Bolts loosening used to be really common on DH bikes when they weren't designed as well as they are nowadays. Trial bikes only recently caught up.

 

[steviedsolve]

Thread lock it. this often happens because of poor tolerances/fit in replacable hanger design as much as torque. vibrations when descending and cornering forces will have more effect on loosening the bolts. Bolts loosening used to be really common on DH bikes when they weren't designed as well as they are nowadays. Trial bikes only recently caught up.

Yes thanks Gary. I forgot to mention I'd used copious amounts of threadlock to solve the problem. Surprised at how little threadlock is used on new bikes. I've also had to do the stem, some brake disc bolts and even a pivot bolt.

 

[Gary]

BITD we'd completely strip new £2k DH frames to threadlock every bolt.
Giant were about the only company I remember who actually threadlocked their pivot bearing bolts.
not using threadlock (or a torque wrench) keeps assembly costs down and profit high

 

[MattyB]

My money would be on a wobbly hanger as previously discussed, or maybe an incorrectly adjust limit screw that let the chain go into the spokes at high torque. It certainly wasn’t the combined torque of motor and rider; that were really possible then this would be happening over and over again on ebikes.

 

[dirkbike]

Awesome I'm more at ease knowing I should be able to tackle these steep climbs that were never even imaginable before the ebike.

I went through the bike. Got maybe 1/8 of a turn out of some of the linkage bolts, the hanger is tight, it could be bent though, it shifted fine but I guess if it's tweaked slightly as @steviedsolve mentioned it could have done it, I'll check it tomorrow with the gauge when I throw on a new derailleur. I actually tightened both limits before this ride as it left the shop with too much over throw for my liking - that or maybe it had gotten bent and I had to adjust it. I don't know, I certainly can't check it now. There is a spoke that's mangled but my initial thought was it broke and then went into the spokes, perhaps under torque, it twisted itself into the spoke? I don't know. SRAM may warranty it, if not I'm not too upset, luckily derailleurs have come down a ton in pricing. I'm more upset about the chewed up paint than anything :/ We'll see if Specialized can send out some touch up paint.

I'm gonna get a new GX tomorrow from the shop, and go back to this hill and hopefully conquer it.

Thanks for everyone's feedback, I'll report back with my findings.

 

[dirkbike]

on 2nd thought, maybe it bent when @iridesworks fell into my bike clipped in lol

 

[dirkbike]

Yep, bent hanger! Totally happened when he fell onto my rear wheel, didn't think anything of it at the time but makes sense. $100 and change later I'm back riding

 

[steviedsolve]

Glad you got it sorted Dirk. These expensive things we learn along the way. I carry a spare hanger now for my Haibike but two years later an no issue. No doubt it'll be something else I don't have a spare of next time.

 

[r23ves]

Hey guys, @dirkbike here.
It didn't get caught in the spokes, nothing weird. It snapped off, went into the spokes, and smashed into the seat stay. Has anyone experienced this before?

My derailleur broke off today in a similiar situation to yours. Going up a hill in turbo hit a bump and it snapped clean off. A stick might have got caught in it, i'm not 100% sure as I wasn't riding it at the time.

Bit annoyed as I had to push home and the chain has scratch the rear triangle now. Hoping specialized will warranty it though.

 

[outerlimits]

I find the SRAM mechs to be weak junk.
Next time I have a problem, I’ll be fitting a Shimano.

 

[njn]

Notice how mine broke off in a different place than the other ones posted. This was caused by a stick.

 

[Gary]

My derailleur broke off today in a similiar situation to yours. Going up a hill in turbo hit a bump and it snapped clean off.

Being in turbo is irrelivent
Your mech cage plates are twisted. This shows the mech was caught by something (most likely by your spokes) and forcably twisted until the aluminium near the mounting bolt sheared. It did not break from the added power from the motor.

If caught by the wheel rotating (by a spoke or even a stick in your spokes) a mech is going to very quickly be pulled past it's designed pivot range therefore it will break at it's weakest point (Which also depends on the direction of the pull/twist).
If hit by an object (rock etc.) a mech or hanger can break catastrophically. for a mech this can be at a pivot, cage or more often than not the aluminium near the mounting bolt.
This happens more often now that rear thru axles are the norm. Replacable QR dropout mech hangers were loads weaker and less stiff so in a lot of cases the hanger used to break before the mech did. occasionally saving the mech from damage.

#science

For this to happen to you guys less often pay careful attention to mech clearance from trail odjects as you ride, when riding through or close to overgrown terrain listen out for anything in your mech spokes and if you suspect anything is in there stop pedalling and pull over to inspect it.
before, during and after rides pay attention to the condition of your mech/hanger/rear axle. (if any one of these are loose/bent/damaged it will often show up as gear indexing becoming sightly out).
A shop may be generous and offer you a new mech (or a reduced price replacement) but don't expect this and if they do be greatful. None of the above are genuine warranty claims.

 

[r23ves]

I'm not going to warranty mine so instead I bought an SRAM XO1 Cassette and Rear Mech to upgrade from the NX. I'm trying to fit it now but the cassette doesn't fit on the hub!

I've now learnt that aparrently the NX uses a shimano hub. Does anyone know if I can I buy a SRAM XD driver and change the freehub or is the casette just completely incompatiable?

 

[Gary]

it would help if you said what hub you have. XD freehubs are available for many hubs. Google will tell you very quickly if yours has.

Personally though. I wouldn't use an XD cassette on an Ebike where that 10T cassette sprocket is going to get a lot more use than a non-Ebike. The 10T also has less chain wrap so it will slip sooner once it and the chain are worn.
It also doesn't make a lot of sense "upgrading" to an ultra expensive XO1 rear mech when you're a mech destroyer. They're lighter. but not particularly stronger. Especially where you broke yours.
Same with cassettes. All that money you're throwing at XO1 is only getting you a lighter weight product. Functionally it's all the same (apart from shifters)

 

[r23ves]

it would help if you said what hub you have. XD freehubs are available for many hubs. Google will tell you very quickly if yours has.

Personally though. I wouldn't use an XD cassette on an Ebike where that 10T cassette sprocket is going to get a lot more use than a non-Ebike. The 10T also has less chain wrap so it will slip sooner once it and the chain are worn.
It also doesn't make a lot of sense "upgrading" to an ultra expensive XO1 rear mech when you're a mech destroyer. They're lighter. but not particularly stronger. Especially where you broke yours.
Same with cassettes. All that money you're throwing at XO1 is only getting you a lighter weight product. Functionally it's all the same (apart from shifters)

Thanks for the advice. I did end up getting new wheels in the end with an XD hub, plenty of other ebikes use the XD. I went 36T at the front so should be using the 10T less as well. The NX casette is really heavy so i'm glad I swapped it out.

You were right about the derailleur, seems functionality identical - doesn't shift any better (or worse) and the weight difference is negligible. The bracket that broke on my derailleur looks exactly the same alloy casting on the X01 so no improvement there either.

 

[Gary]

No worries.
But I think you might have misunderstood what I was saying about using XD. the XD driver cassette interface is IMO a lot better than Shimano's HG splined interface. It#s the use of tiny faster wearing 10T sprockets with less chainwrap that I'd avid on an Emtb. Especially in poor conditions.once you get as low as 10 or 9 teeth the tooth pitch/angle becomes less than ideal.
not saying not to do it. Just saying I personally wouldn't. (I have and like XD on another non Emtb)

What you are paying for in the highest end derraileurs is generally slightly better quality materials, more machining, better tolerance in pivots and occasionally sealed bearings. And in the case of newly released groupsets you are paying for the new features. (12spd, clutches, Di2 etc.) The highest end derrailleurs are rarely stronger than mid level components unless you go to a dedicated DH derailleur like SAINT. and even then it's negligible. The best way to look after a rear mech is to pay mor attention to what your rear dropout is passing
I wish you luck with your new one.

 

[Manc44]

Was it on with 8Nm to 10Nm?

Regarding it snapping, the strongest rear mech I have ever seen or used was a Saint M810 (9-Speed).

Problem is they didn't make a SGS version, only GS and that's possibly the case with 10/11/12 speed ones.

Since Saint stuff is for downhill use, it's built like a tank.

 

[Hamina]

Bit annoyed as I had to push home and the chain has scratch the rear triangle now. Hoping specialized will warranty it though.

Don't worry about the small scratches:

 

[Black8917]

I would check chain length, when I received my rail the chain was too short. When shifted into the lowest gear, the largest cog, disconnect the rear shock or let the air out and compress fully. Mine would have snapped my chain at 50% travel compression.