I broke the rear derailleur on a borrowed bike. I'm trying to understand why.
Until two months ago I knew nothing about bicycles. I bought a worn down cheap second hand bike. It took me way more time and effort than I thought it would, but I finally managed to ride down park lanes and quiet streets, take wide turns, brake, shift gears, with no major incidents other than scraped knees.
This past weekend I borrowed another bike and rode almost entirely on road, just a little going off road and no off road slopes. Then tried a few slopes on the road. All was great. This bike is newer and feels much nicer than mine. It's similar to this but an older model:
I got the confidence to roll down a long rather steep slope, on road, with a few turns and hairpins. It seemed like I went really fast, felt like well over 50 kmh, though I'm not experienced enough to tell. I kept engaging the rear brake gently and managed to keep control all the way downhill, then stopped smoothly.
Then I started climbing back up. I changed gears, then only went a few steps from the base of the slope when bang! The rear derailleur (as I now found out it's called) snapped in two. It's not the hanger or the chain; these look fine to me. It's not bent. It's broken like a twig. As if it was made of plastic. It can't be plastic though, can it?
This is the type of derailleur that broke:
Some more details, as I remember them:
The bike was bought new, but the person I borrowed it from says he "swapped a few parts". Haven't asked what and I don't want to bring it up again.
For the past two years or maybe more the bike sat unused in a shed. To my eye it doesn't show any visible signs of wear or decay, other than the set of sprockets at the rear is partly rusty. They still turn fine I think.
I dusted it off, inflated the tyres and sprayed the chain and sprockets and the front and rear with a spray labeled "anti rust", in the naive belief that it would remove the existing rust somehow.
I read somewhere that going "big-big" is a no-no. I wasnt't. I was using the small chainring (of three) and the second largest sprocket at the rear. So I was going "small-second big", if you will.
I set the saddle a bit low for my taste, but as I'd been using it interchangeably with my kids, I thought I'd just leave it at a height somewhere between what they needed and what I needed. So a bit low for me. This made me tire more easily.
The bike has a thumb lever gear switch. The gears switched fairly smoothly one step at a time, but a few times pressing the lever had no effect, then pressing it a second time made the chain jump up or down two steps at a time.
Before I was confortable switching gears, I would get off the bike, press the lever, lift the rear wheel by the saddle with one hand and used the other to turn the pedals, thus switching gears. Then I got comfortable doing it while cycling.
The stretch of road where it happened is used by lots of cyclist, including kids and older men and women riding ancient rusty bikes, sometimes carrying bags on the handlebar. So it wasn't like some extreme piece of road.
The road had fresh tarmac, felt very smooth.
I weigh 92 kg, that's about 200 lbs.
Was I in the wrong gear? Small front sprocket out of three, second largest rear sprocket out of nine. So second speed overall.
Did I overuse the rear brake going downhill? Could this have anything to do with it?
Am I too heavy for this bike (200 lbs)?
Did I ruin the derailleur by changing gears "manually" a few times? (see above)
Is it a low quality derailleur? I thought Shimano is a good brand, correct?
Was it the wrong (too low) saddle height?
Was is the rusty sprockets at the back?
Was it the "anti rust" spray?
I'm really trying to understand what I did wrong because I don't want this to happen again. My bike is a lot more flimsy and worn out than this one, and now I'm afraid to even get on it at all. This one looked good and sturdy and it turns out it's so fragile.