Ugly GRX RD failure...
 

Wife and I went for a fine ride yesterday in and around St-Émilion, France with pals, we on our own bikes, they were on rental ‘gravel bikes’ set up with GRX. Going up a slight hill, but maybe the best hill of the day, my buddy’s bike experienced catastrophic RD failure, illustrated in the pictures attached.

The pitch on the climb near the end of the ride of about 35miles led to an upshift for him. That had previously been ok, but at this juncture, there was a little skip to the shift, and then BOOM, the plastic covering on the upper hinge of the derailleur cage exploded, the chain jumped, then locked. The activity appears to have bent the cage. He was quick enough to release his shoe to keep from going down on his side, otherwise... who knows. He's had a lot of bad luck in the past few years.

Has anyone seen this before on a GRX set up, or any other? Any theories as to cause? He has to take this back to the rental guys and 'discuss' the situation with them. I was right behind him, and no way he did anything abnormal, experienced rider and all that. Also, if I was right behind him, he wasn't going fast!

Thanks for any observations. BTW, a ride picture to be posted in Photos from rides.

Is the chain in the spokes? That would tear apart a derailleur.

When I took these pictures, yes it was. I heard the loud pop, but can't say when in the sequence of events it occurred. The hill wasn't enough grade for him to shift all the way into his biggest cog, though, so there's that.

Could have happened for any number of reasons, such as the derailleur limits not being set appropriately, bent RD hanger, or another part failure in some way.

Obviously can't be sure whether anything was broken/damaged beforehand, but at least your friend is safe and no injuries!

Yes, safe and no injuries was a big bonus! He and his wife rented the same bike for each of them, and hers had initial derailleur skipping problems, corrected after adjustments to the limit (and B?) screws. He said his was starting to feel as though the same issue was cropping up not long before the seizure.

Rental bike, I'd put my bets on possible previous damage or something.

Rental bike, I'd put my bets on possible previous damage or something.

If they delivered bikes at that price point to you all out of adjustment the rental place probably just isn't that good to begin with.

FWIW I bought both a GRX 800 11spd groupo and an Ultegra 11spd groupo this year. My understanding is that they're supposed to be ~ the same level of technology and quality -- but I've been pretty unimpressed with the GRX shifty bits. Tough to set up, low(er) quality materials and finish, easily disturbed. Ultegra has been as advertised.

ShimaNO

Easy to blame Shimano but I agree that's either a limit screw that was set wrong, a bent hanger, or even a combo of the two.

This is why we have dork discs, people!

We can't know if it is cause or effect, but the first photo shows that the hanger is bent. As this was a rental bike, it probably gets knocked around quite a bit. It's not unusual for a hanger to bend when a bike falls over onto its right side. Even if the limit screws were set perfectly when the hanger was straight, if the hanger gets bent inward the derailleur will be closer to the spokes. And once that happens, it doesn't take much for the derailleur to go into the spokes, or the chain to drop into the spokes - in either case, the derailleur can get mangled.

So, the usual suspects in cases like this are mis-adjustment, abuse, or a combination of both (and both could have happened before your friend picked up the bike, so no error on your friend's part were required).

Soup sandwich of a bike. Wrong pads for the rotor or wrong type rotor for the pads, filthy cassette, RD shows signs of impact to the knuckle prior to this incident.

IMO the RD pushed the chain into the spokes first, probably from a bent hanger (to whatever degree), limit screws not properly set (especially if a wheel change was done), and then the knuckle failed.

If the knuckle failed first the RD would collapse down the cassette to the smallest cog, and actually probably jump off and jam between frame/cassette.

Anyone else have money on chain-too-short? One of the first bikes I built had a pretty similar failure when I went big-big. (Campy Chorus, btw - chain to short or derailleur in spokes kills every groupset regardless of manufacturer).

I've been using GRX for 4 years on a Cutthroat in all kinds of conditions, mud, snow, ice, frozen mud. Never missed a shift and bombproof.