First one was a 40 year old Schwinn Continental. I somehow managed to snap the steel beast's right chainstay near the rear wheel hub. I rode this bike as a commuter for many years, in conditions ranging from snowing at 10F to rainy at 100F. I had an experienced welder friend weld it back on and it has held well for 5 years since.

Second break was just recently on my aluminum Diamondback Podium 3. I snapped the right chainstay near the bottom bracket, at the weld. Since this is an aluminum bike, I've read it cannot be fixed safely unless a reinforcement pipe is somehow put in place, making it prohibitively expensive given a new frame might be the same cost or cheaper.

Possibly the chainstays are breaking due to a combo of my weight, riding style, weather conditions, and usage:

1. I'm a clydesdale at 220 lbs.
2. I lean more towards mashing at ~75 RPM, and I like off-the-saddle riding and hill repeats.
3. I ride year-round assuming no heavy rain or snow. Living near Chicago, the streets are salted so I don't know if that had a role in the chainstays breaking.
4. On the aluminum bike, I would often do hill repeats with my toddler in the carrier behind me, along with plenty of flat riding. This carrier attaches to the rear wheel hub.

So, some questions:

-Am I being too hard on the bikes, or am I just trying to justify what is actually a coincidence/random? After also breaking spokes, rims, chains, and pedals, I am starting to think maybe it's something I am doing.

-Are those carriers known to cause issues with frames breaking?

-Assuming proper welding technique, there's nothing dangerous about riding a welded steel frame, right? I'm actually thinking about pulling the carrier with this bike now.

Thanks!