Mechanical failure - advice
 

Noob here,

Last Friday I was cycling to work as usual and was riding out of saddle when something 'popped' and my left foot dropped at speed and, from the best deductions I can make, a chain slip caused the bike to seize up I ended up going over in a tangle at quite some speed.

Result = both right shoulder ligaments torn (will never heal), cracked rib, severe calf pull and numerous grazes and impact point bruises where I was in a spin (darn clips). Fortunately my helmet took the dent destined for my brain.

Now the bike's crank is still in tact, but it seems the chain popped off the rear freewheel to the wheel side. I suspect that at speed that caused a rear wheel jam that took me down. I'm still in too much pain still to give it much of a look over - but the chain is sat to the wheelside of the cog (though it still rotates).

My main question is why would this happen? The bike's new from the beginning of the year. I did have freewheel bearing issues so had it changed a few weeks back. Since then I felt the occassional 'slippage' but didn't think it was of major concern. That could be my lack of experience of course - could this be mechanical failure brought on by poor work? Or is such a jam not unheard of? How can I go about ensuring this'll never happen again ('cos after the 6-8 weeks this'll take to heal I am, frankly, a bit worried about getting back in the seat)?

Cheers,


Mike

I'm sorry to hear about this. I hope you get well soon.

1) What kind of bike?

2) Fixed or single speed?

3) If you felt occasional slippage, why did you not investigate?

It sounds like you dropped your chain either due to a really loose chain or perhaps flexing the rear of the bike which can severely move the chainline. The latter is possible if you are a big or strong rider and the bike isn't very stiff.

Was your chain too slack?

http://static.howstuffworks.com/gif/...-bicycle-5.jpg

It's a 2010 Marin Inverness single speed. Slight slippage only happened once or twice and I thought it was more a case of brand new part 'finding its feet'. How wrong I seem to have been. Perhaps the chain was more slack after this part was fitted? - though assuming the same number of links and part sizes I don't know why that'd be the case.

I weigh in at about 95kgs. I cycle fast, so there's a lot of force going down - especially when out of saddle. I was probably hitting 25mph+ downhill when I went over.

So when I take my bike to a new mechanic and explain what's happened should I get the chain extra taught to counter my weight or will that only cause its own issues?

It's possible I s'pose, but it had been rigid for the 8 months I've had this bike. Unless the bike shop ****ed up the freewheel cog fitting in a rush job - I wouldn't be surprised if they were getting pissed off with me as I'd complained in writing and been in four times with a recurring issue (broken bearings after 8 weeks) that I was adamant they should fix (and eventually got them to do a changeover free of charge).

Glad you're okay, but what happened to you is the reason why I rarely and I mean rarely ever get out of my saddle. I had a bad accident on a friend's bmx when I was a kid, racing a cocky tomboy. We start, I almost get up to speed, chain slips and I do a GNAR-SIK skid on the ribbed rough concrete sidewalk with my right hand, left knee, and face. 20 years later, I still carry the nice scars from that incident and a weird sense of caution.

I suspect I'll be the very same... Just got back from hospital appointment and consultant may choose to operate (which is unusual).

Sorry about your terrible accident.
I think it was freak incident. I've had this happen a few times but it didn't cause the wheel to seize.
The freewheel it happened with was a very very cheap no name freewheel that came with a cheap bike.
After I replaced it, it didn't happen again.
My theory is that the old freewheel wasn't spinning truly either because of it's cheapness or because the cone wasn't tight enough.

Yeah, it sounds like your chain dropped.

The chain has an easy to find "sweet spot" of operating tension. It should not be tight. It should have about 3/4" up and down play in it so that it may operate without friction or binding.

I would guess that either the mechanic didn't set the tension properly, or through the course of events, you pulled the rear wheel forward in the dropout which loosened the chain.

This stuff happens. But, it's one of those things you must check in the pre-ride check like when you inspect the tires for air. Or you can get a chain tensioner which would guarantee that the wheel does not move forward, but will add some effort to the task of removing the wheel for flats and whatnot. Small price to pay for peace of mind.