Is my chain too long?

[Bollards]

Dear experts,

Just got a new bike (Ridgeback) panorama. After 5 years on a mountain bike I like the greater speed and the less effort needed. But...

When playing with the gears (different combinations etc) I find that when I'm in the middle chain ring, middle ?cog(at back wheel) that when I coast the chain becomes dangerously slack and droops below the chainstay and can fall off almost into the back wheel. An interesting situation when trying to accelerate over a juction.

Chain set: Shimano Deore 48/36/26
Rear Derailleur: Shimano Deore XT
Front Derailleur: Shimano Deore

Is the chain too long?
Are the deraileurs set up incorrectly?
Are the gears less forgiving than on a mountain bike and I'm using them incorrecly?

[Sergeant Pluck]

What happens if you are in small / small front and back - i.e what position is the rear derailleur in? And same question for big / big front and back.

[Cunobelin]

Could be a freewheel / dérailleur problem as well.

Try rotating the cranks backwards. If the chain is not passing through these smoothly and freely you will get a sag in the top run of the chain.

[Bollards]

Thanks for your help.

small / small front and back - Chain becomes slack and hits chainstay. Derailleur position seems in line with small back.

big / big front and back -  Chain's ok, if at an angle,derailleur again seems in line with big back.

[Polar Bear]

One possible reason:

Had a weird one like that with Mr's PB's bike a couple of years back.  It transpired that there is a spring hidden in the body surrounding the bolt that attaches the mech to the frame hanger.    Once dismantled and cleaned, greased and reassembled it worked well for another few months but then the problem returned.   Mech consigned to spares and replacement fitted, problem disappeared.

As it's new why not get back to the dealer and get it sorted there?

[Biggsy]

Once you are sure the derailleur and wheel is in the right place, the chain does not need to be longer than to work with the largest chainring and largest rear sprocket combination.  Have a look at the Sheldon Brown and Park Tool websites, and feel free to post pics of your bike here (pref taken from the side).

As mentioned already by Cunobelin, and worth repeating in case it got lost in the noise, the freewheel or freehub could be to blame if the chain is going slack when coasting.  Unfortunately it's a classic symptom of a knackered freehub.

[Sergeant Pluck]

Thanks for your help.

small / small front and back - Chain becomes slack and hits chainstay. Derailleur position seems in line with small back.

big / big front and back -  Chain's ok, if at an angle,derailleur again seems in line with big back.

I was thinking more of how the derailleur jockey wheels were taking up slack, but anyway it does sound as if one possibility is that the chain might be too long - agree, take it back. 

[Bollards]

Dear All,

Just back from the bike shop.

The reason for the chain becoming slack was some sort of chatty plastic guard next to the back cogs becoming slightly dislodged and interfering with the hub mechanism making it unable to freewheel.

You would think that Ridgeback could make a robust piece of plastic there if they're going to put something in a critical area.

Thanks again for your help I appreciate it.

[Sergeant Pluck]

I guess the key clue (that I didn't pay enough attention to  )was that it happened as you were coasting.

Glad it is fixed.

I hate those spoke guards.