Don’t know if this would help, but I went to this rear mech after the chain just going nuts and leaving the top of the chain stay a total mess. We don’t have the smoothest rail trail, and roads/trails around here. A couple other riders have gone to this too. 
100% it’s the chainring
Wouldn’t be the first brand run by a bunch of cowboys charging good money for junk product
8 Likes
The quick answer is to reinstall the factory chainrings (relatively simple) and see if you can replicate the issue. (Assuming you still have them).
But yeah, that kind of flex from thumb pressure is kinda terrifying. I’d be shocked if that wasn’t the issue.
7 Likes
I had a KMC chain that would throw its self off no shifting, after a few hundred miles it warped visibly when doing it again. Whilst it looked genuine and so did the packaging, part of me suspects it was a fake. I’ve never had a problem with a chain randomly throwing itself again 
Agreed, ditch those chainrings.
1 Like
Thank you all. You have all been a great help for what was a scary moment.
Everything should be genuine, chain and cassette are from authorised dealers and arrived in full packaging.
The Shimano rings will be going back on for now. I’m hoping Dura ace 12 speed chainrings will fit the Ultegra 12 speed crank so I can get the gearing needed for TTing and then just use an Ezdisc cover as mentioned above to hide the mismatch.
Otherwise I assume Rotor are a trusted brand that have been raced on?
I guess Alugear chainrings are fine when they are MTB sized and 1x. Their 2x big rings need a lot of work. They have emailed back saying they are reworking their chainrings to strengthen them and would like me to test those but I think I am just too scared to ever sprint on them again and I shouldn’t be afraid to ride my bike.
2 Likes
Dude, thanks for sharing your story.
In same situation as you. Ultegra DI2, 54-40 Alugear chainrings since beginning of 2024. Canyon Ultimate CF SL.
Crashed about a week ago in a race when putting full force on 54x11 (not shifting). Chain immediately popped of and hit the deck at 60kph. Nothing broken luckily.
I don’t see the same amount of flex in the chainrings by pushing on it as you do, but have a feeling the chainrings are at least part of the issue. Haven’t changed anything else in my setup since last year and derailleur adjustment seem fine.
Will be spending a bit of cash and switching to Dura Ace chainrings 54-40…
Couldn’t find any other bad experiences with Alugear on the internet, but maybe because they’re still a new brand. Hopefully this fixes our issue 
2 Likes
Wow, thank you for letting me know that.
I’d definitely have a go at filming it on the turbo and emailing them.
Are you going to fit the Dura ace chainrings to your Ultegra cranks? That seems the cheapest option for bigger gearing while still being safe and shifting well.
Same exact hole pattern and mounting.
Hell no. I wouldn’t trust anything form those guys at this point.
2 Likes
It’s the chain rings. You should not feel any flex with chain rings, especially road chain rings. (An exception are small mountain bike chain rings, where stiffness suffers both, on account of their size and the minimal “meat” around them.)
Going by their name, alugear, are they made out of aluminum? Aluminum is softer than steel.
I have a Rotor chain ring on my mountain bike and there is no way I can deform it with one finger. It has features machined into its backside to increase stiffness, and stiff they are.
Most chainrings are 7075 aluminum. Including Shimano. It’t the design that’s the issue, not the aluminum.
5 Likes
And Rotor. I know. My point was that the fact it is aluminum exacerbates the issue. You need to account for that in the design.
I would suggest selling those chainrings.
I recently upgraded to a 54t, however went for the shimano offering. It’s great.
1 Like
I would suggest cutting them in half and putting them in the recycle bin … assuming the maker refuses to take them back for a refund
7 Likes
Yeah will contact them as well.
And might go for full DA crank in one go. But Ultegra with DA chainrings will work equally well.
Bit more expensive but better safe than sorry this time.
Or just ride it. No points awarded for matching bike components at the finish line…
Glad you are figuring this issue out this way rather than a big wreck with others around. So much force on cranks/rings/chains, not a place to take chances.
“Or just ride it.”
That’s the best advice. I have an ultegra crank with a dura-ace oversized chainring on it…one side is silver the other side is black. It looks absolutely horrible.
Nobody has ever noticed.
Oh, we noticed.
8 Likes
I prefer when they take notice and look down on me for not bowing to the cycling styling guidelines. It makes it that much sweeter when I see them disappear in my little “fred” rearview mirror mounted on the end of my bars.
It’s cool if some folks want to use their bike as a fashion statement, but I personally don’t get it and I really don’t get it when people get put off by bikes not conforming to standards (like people giving crap about head tube spacers or stem angles). It’s a tool, meant to be used hard and get dirty and scratched.
4 Likes