This one is near and dear to my heart. I've had my bike's derailleur dive into my rear wheel a couple times. The last one was truly out in the middle of nowhere. The worst possible time and location to have a serious breakdown.
There's nothing more frustrating than tooling along on a great ride and having your derailleur dive into the spokes on your rear wheel. It totally "f's" up your day. See the notes at the end on how to avoid it.
I was on the first day of a 7 day bike ride from San Francisco to San Diego. I just got off the plane a couple hours earlier to begin my annual adventure. I took the earliest flight out of San Diego. Just me in my cycling garb and my bike boxed up in the cargo hold.
Upon landing I wait for my bike to come through the special door next to the luggage carousel. I put my bike together right there in the terminal as everyone looks on curiously. I double and triple check everything. At least I thought I did.
After a few hours of climbing the mountains between the San Francisco airport and the coast line I found myself on a pretty lonesome road that began my downhill. There was just one little uphill section that required a downshift into my granny gear. That's when my real adventure began.
I heard the metal crunch sound but by the time it registered and I was able to stop it was all over. My derailleur dove into the spokes of my rear wheel. It broke the hanger off, chewed up spokes, and bent up the derailleur itself.
Now what?? I don't even have cell reception. No cars to flag down. A few houses off in the distance. After walking for about about 30 minutes I got 1 bar on my phone reception. Enough to call my good friend Ken who owns Mike's Bikes in San Francisco. He came to the rescue by sending out one his store managers to come get me. An hours drive away.
Normally the derailleur can be salvaged. Mine was not. Of course it was a not so common electronic derailleur that no one had in stock. But that's a whole different story for another time.
Therefore, I speak from experience when I make the following suggestions:
Here's how to avoid what I went through
1. Keep in mind your derailleur is attached to your frame with a soft piece of metal called a hanger. It's made to break before causing major damage to your frame. Therefore, be careful not to bend it
2. It's best to lean your bike on something but if you lay it down do it on the non drive train side
3. Don't shift under load (take pressure off your pedals while shifting)
4. Inspect your derailleur hanger before each ride to see if it's bent. Definitely inspect right after any spill on a bike
5. STOP pedaling immediately if your derailleur ever dives into your spokes as you shift into the easiest gear
6. Be careful transporting and storing your bike so that nothing bangs into the rear derailleur
"It's your world, Ride it"