Trek Rail - Carbon Frame Crash Damage

[Mikerb]

There are too many variables with carbon ...so much dependant on the composite lay up, the design and opportunity for variable manufacturing quality. Add to that regardless of layup carbon is brittle so not the best material where point loaded impact is likely. Repair is possible but requires expertise and is expensive. By comparison hydroformed ally has radically improved the possibility to design frames with less weight than before, with variable profiles and skin thickness to design in flex or strength as required...and is both lower cost than carbon and easier to mass manufacture with constant quality control. Ally can deform rather than crack on impact and is not as subject to UV damage as carbon.
So for me, I see ally as being the optimum choice for Emtb frames.

 

[Wilbur]

This is clearly a Trek-UDH design flaw as I can't find any reports of the same carnage occurring on other brands. As such it should be covered by Trek.
The fact that Trek are now suggesting the UDH bolt torque should be reduced from 25nm to 15nm to avoid breaking the UDH shows they don't have confidence in the implementation.

 

[Mikerb]

The UDH is supposed to be able to move back on impact and the 25 nm torque is designed to determine the degree of force necessary to do that. The UDH is supposed to have a limit in terms of how far it can rotate backwards dictated by a stop on chainstay.......thereafter the UDH should break. From what I saw on pictures of the UDH embedded in the back of the chainstay dropout, the UDH stop on the Trek was not strong enough to stop the UDH either because the stop was just carbon or an ally stop embedded in carbon.

 

[torabora851]

The UDH is supposed to be able to move back on impact and the 25 nm torque is designed to determine the degree of force necessary to do that. The UDH is supposed to have a limit in terms of how far it can rotate backwards dictated by a stop on chainstay.......thereafter the UDH should break. From what I saw on pictures of the UDH embedded in the back of the chainstay dropout, the UDH stop on the Trek was not strong enough to stop the UDH either because the stop was just carbon or an ally stop embedded in carbon.

The bolt from the derailleur hit the frame first before the UDH reach the limit. So the force is applied to the derailleur and chainstay, omitting the UDH that is supposed to get all damage.

 

[Wilbur]

That shows there is definitely something wrong with the Trek design. My take on UDH is that it is NOT designed to break in the same way that a traditional hanger is, but instead absorb the impact by rotating (otherwise you wouldn't see Nukeproof and NS Billet making tough CNC aluminium UDH).
The issue with the Trek implementation seem to be that the UDH can rotate too far, allowing the derailleur to get dragged up by the cluster, causing all the ensuing damage.

 

[Sophie777]

What did you do? That is terrifying. I've never owned a carbon frame and never will. Too expensive and to fragile for mountain biking. Clearly.

I was riding home from the bike shop, maybe a km away. The road was pretty busy, with cars flying past. I decided I should get on the sidewalk. There was some gravel on the curb of the sidewalk - which I saw. But I said to myself this is a "gravel bike", so I'll be okay. Upon mounting the curb of the sidewalk from the road (almost parallel), the front wheel lost traction, and I fell on the drive side of the bike. But both seat stays cracked, as well as the left chain stay.

Initially I thought the crash was 100% my fault (bad judgement, bad rider). But later on, after thinking a bit about the crash, I thought perhaps Specialized had some fault, as the bike was marketed as a "gravel bike", yet came with relatively slick tires. I did not mention this to the bike shop; I already had admitted fault.

 

[Nautical Biker]

That shows there is definitely something wrong with the Trek design. My take on UDH is that it is NOT designed to break in the same way that a traditional hanger is, but instead absorb the impact by rotating (otherwise you wouldn't see Nukeproof and NS Billet making tough CNC aluminium UDH).
The issue with the Trek implementation seem to be that the UDH can rotate too far, allowing the derailleur to get dragged up by the cluster, causing all the ensuing damage.

That seems like a reasonable explanation.

 

[torabora851]

Had a similar issue today on Turbo Levo - a branch blocked the derailleur. The result is a broken derailleur cage and bent UDH hunger. The hunger rotated for about 30 degrees and was stopped by a limiter on the frame. The frame is not damaged. That's how it is supposed to work!

 

[Wilbur]

Had a similar issue today on Turbo Levo - a branch blocked the derailleur. The result is a broken derailleur cage and bent UDH hunger. The hunger rotated for about 30 degrees and was stopped by a limiter on the frame. The frame is not damaged. That's how it is supposed to work!

It’s a better result than the Trek examples for sure, but a destroyed derailleur from a branch isn’t a great result. The old bendy hanger may well have preserved your mech. What’s an AXS mech worth these days?

 

[torabora851]

It’s a better result than the Trek examples for sure, but a destroyed derailleur from a branch isn’t a great result. The old bendy hanger may well have preserved your mech. What’s an AXS mech worth these days?

Absolutely. My favourite is the Syntace x12, have snaped that bolt twice on my Norco Range, and replaced it on trail without any damage to other stuff

 

[Gd3fit]

Have a somewhat related issue on my Fuel EXe that was not due to crash, but simply trying to torque down the UDH hanger to 25nm. The UDH ended up rotating through the carbon stopper that the hanger usually rests up against. Crushed the carbon stopper. Trek replaced the seat stay and the Trek store did the labor. Took a week, no charges on my end.

Fuel EXe - Trek Fuel EXe Megathread!

I got my Bike back from my Dealer and got a new Motor now with the width-adjustable Motormounts and the clicking noise is gone 🤌🏼 They talked to TQ and they said it was a running change and the early bikes / motors came without the adjusters. There is no official document or bulletin from Trek /...

www.emtbforums.com

https://www.emtbforums.com/attachments/img_4749-jpeg.122071/

 

[Mikerb]

.........hopefully with a changed design because a carbon "stopper" is a bout as much use as an ashtray on a motorbike!!