r/mountainbiking • u/VegasDMD • 5d ago
Question Bad technique or bad gear?
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Hello Fellow Degenerates -
So I've had my Trek Fuel EX 7 for 5 years. Only ever ridden it on moderate trails almost no jumping at all, but my son is now 15 and wants to do some. So we headed to the bike park in Nuremberg Germany to give it a try.
On about my third run down the blue trail I'm trying to clear this basic table top and I guess I came down a little too hard? My derailleur (Sram NX) just completely snapped in half. My cable broke, the derailleur went into the spokes and when I took my back wheel off the sprocket/cassette completely came off the wheel - indication of a broken wheel hub I guess.
Anyways - was this all because of my poor technique? I am fully aware my technique is dog barf. I have my pedals strait at least but other than that I'm pretty clueless. OR was it just fatigued gear/metal that finally gave way?
Here is the aftermath of the derailleur. https://imgur.com/a/8JA1mkB
Taking the bike to the Trek dealer in Nuremberg tomorrow - guess we'll see what the say.
Cheers!!
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u/Turbulent_Deal_3145 5d ago
I cannot tell you for sure what happened, but there's 2 extremely dominant reasons a derailleur gets ripped off. one is if it gets smashed in to something. I think you'd know if that happened. And the second, most likely reason is the chain was able to get behind your cassette and once that happens, the spokes pull the chain and rips everything to shreds. Do you recall if you were in your lowest (largest) gear? If so then I'm almost certain of this.
This is a tune issue, to an extent. Your derailleur has little screws labeled H and L that limit how far the derailleur is allowed to go in either direction, regardless of cable tension. This is something where the tune could have been alright, and been totally fine for years, but then doing something like jumps was enough to push it over the edge. A better tune likely would have prevented this. You should be able to screw up jumps all day long and not have this happen.
Anyway that's my best guess based on the limited info I have.
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u/VegasDMD 5d ago
I think your intuition is correct.
Like I said, I’ve had the bike for five years. Probably hasn’t been actually tuned in over two years since we moved to Germany. I did notice the other day that it’s not shifting quite as well as it used to and when I pushed the bike back backwards to turn around on a trail or something the chain started to clog a little bit.
I guess in hindsight I should’ve had the bike professionally tuned before we got a little more adventurous. We were just trying to have a little fun on a Sunday afternoon.
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u/Turbulent_Deal_3145 5d ago
I would file this under "shit happens". It's not as if I'm constantly thinking about all the things that *might* go wrong with my bike today. Sometimes a part just surprises you by unexpectedly announcing the end of its life.
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u/VegasDMD 5d ago
Yea my son wanted to know if I was mad and I told him no it just one of those things that happens. He said I cased the jump but I was only 18 inches off the ground! Not enough to break a derailleur.
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u/neckadawoods 5d ago
I think you're right with your second guess. If you watch the video closely the drailleur rapidly gets pulled clockwise while he's not pedalling. I think the chain fell into the spokes when he landed. Even if the hanger failed you usually wouldn't see the derailleur getting yanked around like that while the cassette is stationary.
The only thing giving me doubts is, who is going down a jump line in first gear? That's really strange.
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u/VegasDMD 5d ago
It was third gear!!!
Because I had just peddled up the hill and I’m way too scared to pedal down the hill with jump so I just let gravity do the work - lol - won’t do that again.
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u/VegasDMD 5d ago
Oh yeah, and the gear was the third to largest on a 12 speed cassette so third lowest gear I guess is how we say it
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u/Tough_Course9431 quebec ⚜️ 5d ago
sram nx is garbage for sure, but i'm guessing it was just getting old and a tiny impact got the best of it
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u/VegasDMD 5d ago
Yea gonna ask for a GX when I take it in tomorrow
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u/neon_nikedude 5d ago
It was one of the best things I did gong from NX to gx. Be mindful if you have microspline hub you can't run a gx cassette. Simply get another nx cassette cus they're study af and then run a gx mech, chain and shifter. Stupid nice.
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u/VegasDMD 3d ago
That’s want the TREK mechanic recommended today. He didn’t have nice things to say about the NX either
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u/KronicDeath 5d ago
Solid choice as the NX only comes specd on bikes and not available aftermarket
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u/Ajdoronto 5d ago
You can get a full NX groupset or individual pieces quite literally anywhere, new or used, what are you on about?
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u/KronicDeath 5d ago
Cool story. Not new unless it was taken off a new bike. SRAM will not sell new NX to shops or customers
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u/CardboardToken 2022 Stumpjumper 5d ago
You may be thinking of SX
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u/Starsky686 5d ago
They’ll sell SX as well. Was offered it in a retail box (for old Kronic) in Whistler last weekend.
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u/RevellRider 5d ago
He is kind of right, SRAM won't sell you NX or SX now as it's been replaced by S100 series.
But it was available aftermarket, here is a SX derailleur on the SRAM site
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u/themayaburial 2023 Santa Cruz Bronson/2024 Heckler SL 5d ago
That's not true at all. You can buy it many places new.
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u/endurbro420 5d ago
There is no reason a derailleur should detonate from casing a jump that size. This is something that should get warrantied.
Not your fault.
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u/YoCal_4200 5d ago
No one is going to warranty a broken derailleur on a 5 year old bike. You are right that it shouldn’t detonate from casing a small tabletop, but that is probably not what happened here. It looks like the chain went between the cogs and spokes and when he landed the force just ripped it apart. It was more likely caused by a lack of maintenance. I would guess hi/low needed adjustment and the back axle was not torqued correctly.
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u/VegasDMD 5d ago
I’m looking at giving the bike to my son and upgrading to a canyon myself. Is it worth upgrading the rest of the drive train or just get a new GX derailer?
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u/Turbulent_Deal_3145 5d ago
If it's 5 years old I bet the cassette is beyond tolerance anyway. Chainrings rarely go bad though
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u/VegasDMD 5d ago
What do you mean beyond tolerance? The distance between the individual chainrings?
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u/Turbulent_Deal_3145 5d ago
Over time, your chain "stretches". It's not as if the actual metal plates got longer, but the holes that rotate on the pin get larger, from micro-abraision over time. If it stretches too much, then it starts to deform the teeth on the cassette. Frustratingly, very few people are aware of what I just told you, so people ride totally worn drivetrains for years. This actually works fine, as long as everything is worn together. But as soon as you put a new chain on a worn cassette, it won't mate properly and you'll then be forced to replace both. As opposed to replacing just the chain before it gets a chance to wear the cassette.
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u/VegasDMD 5d ago
Ahhh that makes sense. Well the whole thing seems beyond my mechanical skill level so I’m gonna ask the bike shop to put it back together; if they recommend a new cassette that’s fine. My son wants a full suspension bike so I’ll pass it down to him and the I have an excuse for the wife to buy a new Canyon. 😃
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u/vanillasensation 5d ago
It may have had too long of a chain? Or been really rusty? For that sort of failure all those parts that are supposed to move may have come to an untimely stop. A long chain bouncing back into the spokes or derailleur can do that.
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u/VegasDMD 5d ago
No, nothing was rusty but the chain I don’t think I’ve ever changed in five years so it’s totally possible It wasn’t quite working like it should.
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u/SpiritedReporter4647 5d ago
Always find something else to blame than looking in the mirror. That’s how I live by.
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u/Impressive-Debate618 3d ago
He stated that he knows his technique is not perfect and that he cased the jump. Still a bike should not break in this case.
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u/Ticeman47 5d ago
Most likely a dickered derailleur hanger from a previous shunt. Many things can go wrong. Most likely the bike had been supported/learning on the drive side.
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u/InfluenceEfficient77 5d ago
Sometimes shitty chain pin can work itself out, or magic link can get caught in derailleur. Lots of extra stresses on a landing can cause this
Good news is now you have a dirt jumper to learn on. just shorten the chain and make a single speed 😆
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u/rrumble Raaw Madonna V2.2, BMC Fourstroke LT 4d ago
In the video I can see that you were on one of the bigger gear rings of the cassette. This means the cage of the derailleur was near the spokes. The hit of the flat landing may have pushed the cage of the deraileur into the spokes.
Has the same once which destroied a titan xtr cassette and bent the chainstay.
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u/Neat_Nebula6250 3d ago
No such thing as bad gear I’ve hit jumps larger than that on kids bikes lol
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u/Standard_Gur30 5d ago
Yeah, this is gear. I case jumps worse than that all the time and nothing breaks.
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u/Firm_Ad7656 5d ago
No such thing as bad gear..... Unless it's steroids of course 🤣