This can only happen if you remove your spoke protector. I've ridden with the limit screw improperly set, I tried to down shift , and the chain bounced off the spoke protector and right back onto the largest (smallest gear)! No problem.
Like I said, cross chaining does not have to lead to disaster. Just keep your spoke protector on, and keep the limit screws set properly and everything is fine.
Of course, there may be a bit more wear and tear if you ride 50X12 or 11 a lot, but I'm assuming most people won't.
Originally Posted by
WalksOn2Wheels
Like I said before, if you know for certain your bike is in tune, it's not an issue, but there are plenty of people with der. hangers ever so slightly bent from that one time it fell over while they were leaning it against the car or whatever else may have happened. All it takes is that, or an improperly dialed limit screw to allow your chain to hop over the largest cog and into the spokes. Or if the chain doesn't hop over, the hanger might be just bent enough for the lower end of the cage to catch a spoke and then it's all over.
I saw it just a couple of weeks ago. I was coming up to a turn and saw a guy walking his bike off of the shoulder to the grass. I stopped to see if I could help, but it was pretty clear that he was going to have to make the call of shame. He had the chain on the big ring in front, and the derailleur was all wrapped up in the wheel. He was obviously on the largest rear cog and one of the two der/chain drop scenarios had happened. In that case, the force had ripped the rear wheel out of the dropouts and it looked like the left dropout had been pretty bent up. I guess he could have the dropout replaced as well, but it at least resulted in an expensive frame repair. In an extreme case, you can take out a chainstay.
And he even mentioned this had happened to him 2 times before already.... I didn't have the heart to discuss the dangers of cross chaining as he was already having a pretty miserable day.
EDIT: To clarify, a really bent hanger or out of tune derailleur could also put the derailleur into the spokes while in the small ring, but when you are in the big ring, you are maxed out on chain tension, making it more likely that the cage could be pulled towards the spokes or that the chain could hop off of the cog and into the spokes. If you're lucky, just the chain will fall back there and scuff up your spokes behind the cassette.
But again, for a perfectly tuned bike, it's not an issue. But not every rider knows how to tune a bike.