How To Avoid Dropping Your Chain When Changing Down On The Front.

[boydj]

To avoid a dropped chain you need :
- a well adjusted front mech
- some planning ahead on when you might need to move to the smaller chainring
- preferably be in a gear nearer the middle of the cassette, rather than going all the way to the big cog while in the big ring, which might involve a double change, smaller cog as well as going to the small ring
- to back off the power a little
- use a dog fang or similar if you can't stop dropping the chain

 

[fossyant]

Dog fangs on both road bikes, just in case - protects the paint, especially one that's just been re-painted.

 

[Mr Celine]

I've done it loads of times (dropped my chain onto the bottom bracket when changing down at the front).

Not such a big deal with a steel or Alloy frame, but quite damaging for a Carbon Fibre frame.

Early on, when it happened to me, I assumed I needed to adjust the L screw on the front.

I farted around by adjusting in by an eigth of a turn but to no avail.

So I started to think about when it was that I was dropping the chain.

Always uphill, always under load.

So I thought about it a bit more and wondered why?

Here's my conclusion (shout at me if you disagree).

The front mech gives the chain a gentle shove when you change gears.

When there is little load on the chain, it goes where the front mech tells it to go.

But if there is a load on the chain (maybe you are standing up on the pedals pumping up a hill), the chain is firmly gripped to the chain ring and all the front mech is doing, is applying sideways torque to the chain.

That sideways torque is like an elastic band being bent in the middle. At some point, the front mech will win and the chain will snap left.

The force of the chain snapping back will cause the chain to overshoot the gear change and end up on the bottom bracket.

To avoid this, when changing down at the front, you simply have to pedal "behind the load" (keep moving your legs but take off the pressure for a second or so whilst you change down).

It works for me anyway.

Torque? Hang on a moment you're only applying a sideways force.

 

[GuyBoden]

View: https://www.youtube.com/watch?v=hlbenKUx9JM

 

[Bogs]

I had Campag 50-40-30 with highest 29 at the rear, (not good for ageing legs and loaded touring), Campag said you can't get any lower but a mate put a 24 on the front which is quite a big drop from 40 with chance of dropping the chain if not carefull.
I fitted a "Jumpstop" and never had a problem.

 

[Blue Hills]

I had Campag 50-40-30 with highest 29 at the rear, (not good for ageing legs and loaded touring), Campag said you can't get any lower but a mate put a 24 on the front which is quite a big drop from 40 with chance of dropping the chain if not carefull.
I fitted a "Jumpstop" and never had a problem.

what's a "jumpstop"?

 

[rrarider]

what's a "jumpstop"?

I guessed that it would be some sort of wigwam for winding the sun up and down, but even the 12 year old expert's friend Google failed to produce an answer. If I put the words 'bike' and 'jumpstop' in as search terms, then it did indeed lead to a result. It is as I guessed some chain catching gadget.

As a rider of a vintage bike, with friction shifters, I can't see why the limit screws don't do their job, but hey - what do I know?

 

[Blue Hills]

but even the 12 year old expert's friend Google failed to produce an answer. If I put the words 'bike' and 'jumpstop' in as search terms, then it did indeed lead to a result. It is as I guessed some chain catching gadget. It is as I guessed some chain catching gadget.

yes i guessed that - maybe you'd care to share the link you found - so I can see an actual product that works/has some track record.

You know, help, as in folks on a forum, exchanging useful info and helping each other.

@Bogs seems to have fitted one that presumably works so will await a nice reply from them.

 

[ChangFai]

All these of years of cycling and I never had this problem, until last year when I bought a Planet X.

I think the first time I changed down, chain off and a scrape mark on the carbon frame.

I have looked for a solution since, and the only one I have found is to take it very very easy when changing down.

Bluidy annoying.

 

[ChangFai]

Dog fangs on both road bikes

Thanks, never knew that existed.

I am using helicopter tape to protect the frame at the moment.

 

[rrarider]

yes i guessed that - maybe you'd care to share the link you found - so I can see an actual product that works/has some track record.

Done - link is here

 

[ChangFai]

Any of these anti-chain drop devices (that I did not know existed) work with a carbon frame?

 

[fossyant]

Thanks, never knew that existed.

I am using helicopter tape to protect the frame at the moment.

Two types, dog fangs are a plastic clip that fits the down tube, but if you've got say a fat tubed bike, you can get chain catchers that fit on the front mech fixing bolt - these are a long aluminium 'arm' that bends in towards the chain rings.

 

[fossyant]

Chain catchers for fat tubes/carbon etc

https://www.sigmasports.com/components/chain-catchers

 

[T4tomo]

As a rider of a vintage bike, with friction shifters, I can't see why the limit screws don't do their job, but hey - what do I know?

Limit screws should work, if they don't, its not too much on a issue on a steel (or Alu) frame. On a carbon frame it can cause a very ugly gouge. Some manufacturers fit them as standard (other fit a heavy duty alu protective sticker) I guess some don't bother, which is a shame for the sake of a <£5 cost part particularly when the first time when many buyers realise they might need such a thing is when they are looking at a gouged frame.