I converted a child trailer into a grocery/flatbed trailer. I am pulling it right now with a sort of junker GT MTB.

On the way home from the store yesterday hauling a trailer FULL of groceries and also my 240lbs around, I started hearing bad sounds from the drivetrain. The GT is sort of a throwtogether bike that I picked up from a thrift store and did some quick cleaning and maintenance to. About a block from home (a quick thank you to the very kind and wise bike gods!) the chain gave out.

I know the chain on this thing was old and who knows what crazy person installed it, but it got me to wondering whether hauling a lot of weight on a bike put significantly more stress on the chain. I suppose that it does not help that I am not only heavy, but also am pretty strong. I have broken only one other chain in my life while riding, and so I am wondering if this is a more common problem while pulling weight.

jim

I would bet the main contributor was a chain with a dubious history. You don't know how old it was, how well it was maintained (cleaned and lubricated), or how it was installed before you got it. And you imply that you haven't done much with it since. I'd say the bike gods were MORE than kind to you.

Eric

I wouldn't think additional weight would play much of a factor in chain wear or breakage.

In general, as you pull a heavier load you shift to an easier gear. Unless there is some physics property that I am missing (entirely possible), it seems that a 145lb olympic rider who can hammer the pedals down for extended periods would be putting more strain on a chain than a rider like me (215lbs) riding in a comfortable gear. Adding a trailer and the weight it carries would incease drag and put a bit more strain on the drive chain but most of us shift to an easier gear to compensate for this.

Just thinking out loud... I have no background in physics and there are probably a lot of forces at wok that i ignored in my hypothesis. I'm sure someone here will back me up or set me straight.

I wouldn't personally think that the chain is a big risk area for a utility bike. Certainly you exert some extra energy to move your stuff around, but aside from that extra effort there isn't any additional stress being placed on the chain, and honestly, professional cyclists and hard riders probably put out more energy and pound down the pedals much faster than someone riding their bike like it was a small yak

At least, thats how I ride.

I would just go with EricJ's answer, probably just the chain, and you had some pretty good luck.

Yeah, I know that the fact that the bike is iffy is the biggest factor. (I was only tooling around the neighborhood basically; I wouldn't go very far on a cruddy bike that I had not gone over carefully.)

I would think that mashing would put a lot more strain on the drivetrain than spinning. Certainly puts more strain on my knees. So, I was guessing that mashing with more weight would ask more of every link in between my torso and the bottom of the rear tire.

jim

Riding mostly on the small chainwheel will put a lot more stress on a chain, especially with compact gearing. 24:11 and 48:22 are the same gear ratio, but the 24:11 combo puts twice as much tension on the chain.

Chainwear gauges link are pretty cheap. Not only can timely replacement prevent breakage, it can save more extensive damage to the chainrings and cassette.

Rest assured that it was 100% a dodgy chain and 0% your gargantuan strength. Replace the chain, give it some regular maintenance, and you won't have a problem. You'd be surprised just how strong a bicycle chain in serviceable condition actually is.