Chain just coming off

[spandex]

BB's do not deflect

 

[Joe24]

BB's do not deflect

Deflect means move, right?

 

[spandex]

Yes

they do not move side to side!

 

[rustychisel]

Chains don't JUST come off, in my experience. It may be the lateral movement in the frame is allowing it to be pushed off the chainring, but a not round chainring is likely allowing it to be lifted and dropped at the same time.

Bottom Brackets don't move sideways, but the flex in an (old steel) frame, for example, is perfectly capable of allowing the drivetrain to move laterally by ~5mm.

 

[peanut]

Does that mean that the bottom bracket moves from side to side?
If so, thats what ive been told as to why the chainring collapsed, but was said the frame flexed, now that the BB was deflecting.

no the bottom bracket doesn't deflect does it !....it is the bicycle frame that deflects. The bottom bracket goes with the frame . As the frame deflects the bottom bracket and chainset go out of verticle alignment which ships the chain. Rusty chisel has put it much more elequently than I

 

[skwerl]

no the bottom bracket doesn't deflect does it !....it is the bicycle frame that deflects. The bottom bracket goes with the frame . As the frame deflects the bottom bracket and chainset go out of verticle alignment which ships the chain. Rusty chisel has put it much more elequently than I

only under heavy load though. ie when out of saddle going uphill. Joe was heading downhill at the time, I think, so can't see there being enough pressure on the frame to twist it enough.

I think the chain was too slack. When your're pedalling at that rate there's enough momentum to pull cthe chain off if only a bit of it starts to unship

 

[Andy Pandy]

I had a similar problem that was due to the front chainring. It wasn't very round, giving tight and slack spots on the chain. As it was off a geared bike it had a small section where the teeth were smaller (to allow the chain to move off the chainring). Going down hills when there was little load on the chain, and you hit a bump in the road (when the chain was slack) it could simply bounce off the ring.

 

[peanut]

only under heavy load though. so can't see there being enough pressure on the frame to twist it enough.

the pressure is caused by it being a fixed gear bike isn't it if it was a freewheel there would be none but a fixed is in constant connection with your body through the pedals whether pushing to accelerate or pulling to de-accelerate when going downhill .

 

[itboffin]

My chain popped off 2 miles from home on a rapid downhill, further inspection revealed a slack chain and I know the tension was just right when i set out, I don't think for one minute that I'm a powerful or even strong rider but is it possible that the axle or nut are worn?

It was a long ride with lots of hills many of which I had to really stomp to get over.

Both the chain & freewheel are new.

 

[MrGrumpy]

I was advised to buy these and then not worry at all about tension

http://www.tartybikes.co.uk/product.php?product_id=170&category_id=8

 

[itboffin]

I've seen those but how do they work? it's not obvious from the image.

 

[Landslide]

Round bit goes over your axle (twixt either frame and locknuts or frame and wheelnuts), squarish bit sits over the ends of your dropouts. Tighten the nut and it pulls the wheel back in the dropouts. NB: This is only applicable for rear-facing track dropouts.

I reckon Joe's problem is just his sheer power. I bow before your thighs, Oh Mighty One!
(This post may contain traces of sarcasm )

 

[Joe24]

Round bit goes over your axle (twixt either frame and locknuts or frame and wheelnuts), squarish bit sits over the ends of your dropouts. Tighten the nut and it pulls the wheel back in the dropouts. NB: This is only applicable for rear-facing track dropouts.

I reckon Joe's problem is just his sheer power. I bow before your thighs, Oh Mighty One!
(This post may contain traces of sarcasm )

I was in the gym today and did 40 reps of 150kg's on the leg press. Only another 40kg untill im doing the full stack of weights on that machine(only goes up to 190kg)
Mines is infact my sheer force in the legs
Im trying to decide whether to get a new frame(comes with carbon forks, and ill be getting headset, crankset, chain, stem handlebars, seatpin, bar tape) or to get a 2008 Giant Bowery.
The Giant Bowey is £110 cheaper, but the frame looks abit nicer and its got carbon forks.
It really is a hard decision to make

 

[skwerl]

the pressure is caused by it being a fixed gear bike isn't it if it was a freewheel there would be none but a fixed is in constant connection with your body through the pedals whether pushing to accelerate or pulling to de-accelerate when going downhill .

Not realluy.
Being fixed is largely irrelevant. You may be in constant connection but for a fair bit of the pedal stroke you're coasting. You still put most pressure through the first half of the stroke (about 2 o'clock to 6 o'clock). You can't put enough backwards pressure on (esp. when going fast) to twist the frame. the only time you'll see flexing is when you give it the BDC grunt

 

[itboffin]

I was in the gym today and did 40 reps of 150kg's on the leg press. Only another 40kg untill im doing the full stack of weights on that machine(only goes up to 190kg)
Mines is infact my sheer force in the legs
Im trying to decide whether to get a new frame(comes with carbon forks, and ill be getting headset, crankset, chain, stem handlebars, seatpin, bar tape) or to get a 2008 Giant Bowery.
The Giant Bowey is £110 cheaper, but the frame looks abit nicer and its got carbon forks.
It really is a hard decision to make

well mine is because I'm old & too weak to tighten the nuts enough

40 reps of 150kg - PHEW! you sir are mental, in the nicest possible way