DA 9100 cranks - A cautionary tale

So I've had my first Shimano crank failure. It was on my gravel bike. The bonding between the main forging and the smaller c-cross-section insert along one edge of the left-hand crank failed, causing the hollow "torque tube" become structurally incomplete. The crank went flexy as a noodle, especially out of the saddle. I nursed it for 90km and had it replaced with a second-hand XTR crank to get me through to the end of our gravel bike-packing trip.

Now, my puny watts are unlikely to have caused the component any meaningful stress at all, so I'm surmising that it is the effect of standing on the pedals when descending rough roads that was the cause of the stress and ultimate failure. It was about 4 years old. My caution is that road components (even very good ones) might not be the best choice for gravel-biking due the different way they're stressed. Interested in others' experience.
 
You're running DA cranks on a gravel bike? I know things have become more affordable but DA is Shimano's road racing groupset. I never understand why people run this on bikes that it's not suitable for or on bikes they put thousands of miles into. While you'd hope it'd hold up reasonably well, I don't think it's surprising that failures happen.

That said, HT2 cranks unbonding is pretty common (they're also the most common cranks in use on road bikes, maybe even MTB too) as @42x16ss has pointed out.

On gravel I'd personally run square taper if you have the option and aren't racing. If you're racing then GRX/XTP and you'll have to accept that failures are the cost of doing business.
 
You're running DA cranks on a gravel bike? I know things have become more affordable but DA is Shimano's road racing groupset. I never understand why people run this on bikes that it's not suitable for or on bikes they put thousands of miles into. While you'd hope it'd hold up reasonably well, I don't think it's surprising that failures happen.

That said, HT2 cranks unbonding is pretty common (they're also the most common cranks in use on road bikes, maybe even MTB too) as @42x16ss has pointed out.

On gravel I'd personally run square taper if you have the option and aren't racing. If you're racing then GRX/XTP and you'll have to accept that failures are the cost of doing business.
Thanks. Yep, not the best decision in hindsight, perhaps. The bike is pre-GRX, so the main alternative at the time was MTB. Having said that, it's done a lot of miles, including 2 Unbound (back when it had a different name). But yeah, consider me schooled.

I have a gravel new bike coming this week. The back-end is all 1X MTB, and set up for wider tyres, up to 55mm 700C. That'll be me my go-to for the rougher terrain and bike-packing trips. The DA-equipped bike will now be more of an all-road bike, including Unbound again next year. It will continue to also be my winter commuter with different wheels, fenders and a 105 crankset.
 
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Reactions: 42x16ss

Shimano don't make 'em like they used to, stick to the XTR crank or try something that's not two piece
The XTR is also two-piece bonded. It looked like it had done a LOT of miles, but was fine for the remainder of the trip. Bike shop fitted it for $15.00 all-up. It's 175mm rather than the 172.5 it replaced so I had a mismatch. That was less of a deal than you'd think. I could barely notice the wonky set-up. Anyway, the new DA left crank has arrived, and will go back on in the spring. (I switch to 105 for the winter commuting.)
 
Reactions: 42x16ss
Thanks. Yep, not the best decision in hindsight, perhaps. The bike is pre-GRX, so the main alternative at the time was MTB. Having said that, it's done a lot of miles, including 2 Unbound (back when it had a different name). But yeah, consider me schooled.

I have a gravel new bike coming this week. The back-end is all 1X MTB, and set up for wider tyres, up to 55mm 700C. That'll be me my go-to for the rougher terrain and bike-packing trips. The DA-equipped bike will now be more of an all-road bike, including Unbound again next year. It will continue to also be my winter commuter with different wheels, fenders and a 105 crankset.
Fair enough, that's better than I would have expected. Sorry, I think my vent was more general because I've seen too many people in my clubs running cotton tubs or other crazy thin tyres then complain about them puncturing/wearing out quickly (on Scottish roads no less!), high-end derailleurs, carbon handlebars and seatposts and low spoke count wheels breaking through general use etc. and wasn't really directed at you. It sounds like it is a race bike so it does make sense to run decent components.

Sounds like a decent set-up on the new bike, I don't think I've seen nearly as many crank failures for HT2 MTB cranks as I have for road, but again that might just be because there are more options in MTB that you see regularly.
 
Fair enough, that's better than I would have expected. Sorry, I think my vent was more general because I've seen too many people in my clubs running cotton tubs or other crazy thin tyres then complain about them puncturing/wearing out quickly (on Scottish roads no less!), high-end derailleurs, carbon handlebars and seatposts and low spoke count wheels breaking through general use etc. and wasn't really directed at you. It sounds like it is a race bike so it does make sense to run decent components.

Sounds like a decent set-up on the new bike, I don't think I've seen nearly as many crank failures for HT2 MTB cranks as I have for road, but again that might just be because there are more options in MTB that you see regularly.
No need to apologize. It's a fair challenge. I buy the high-end stuff because I've worked my whole life to be able to afford it. I am not totally shocked that I found the limit of DA on a gravel bike that has seen some very hard miles. The comparison of the XTR and DA crank is interesting. They're both made the same way, but the XTR is smaller in outside cross section. About the same weight, so thicker walls perhaps. Also wider on the "thin axis" than the DA. Shimano are not dumb, so I'd expect that the MTB stuff is more durable in the face of shock loading.

But the crankset on the new bike is not Shimano HT2 at all, but a Ti MTB crankset from a small manufacturer that my bike-maker guy assures me is bulletproof. We'll see, I guess.
 
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