changing from a 42t chainring to a 39t - any potential problems?

[nuovo_record]

currently running a 53/42 unfront, with a 13-21 and a mirage short cage mech on the back - so would like it to be a 53/39.
somewhere in the dim and distant past i have read about lengths of mech and chains required, but i'm really not sure how to work it out 

help if you can!
first time out on the bike in 3 years and realised my legs need a bit more help (and yes i need to do more - but it's a start)

[eck]

Shouldn't cause any problems.
The only "maybe" I can think of is you may have to remove a link from the chain in case it wraps up on itself in the 39 - 13 (which you shouldn't be using anyway  ).

[Biggsy]

You'll be fine with the existing mechs and chain length.  It's possible that the position of the front mech may need adjusting slightly, but even that is unlikely.

Chain length more importanly depends on the largest chainring and largest sprocket rather than the smallest ones.  Rear mech cage length depends on the difference between lowest and highest gear, but a short cage will still be fine for your new gears.

Do not remove a link unless the chain is already longer than necessary to work with 53/21.

Good to hear you're back on the bike.

[nuovo_record]

thanks for the help guys.....will try and source a chainring according to my price range!

[David Martin]

thanks for the help guys.....will try and source a chainring according to my price range!

I'll have a look around. I may have a new 39t ring.

..d

[nuovo_record]

thanks for the help guys.....will try and source a chainring according to my price range!

I'll have a look around. I may have a new 39t ring.

..d

thank you