Chain length when swapping from Standard to Compact cranks

dubbs2009

Currently running Standard cranks 53/39T with 12-28T on cassette - considering swapping standard to compact - e.g. 50/34T and keeping the 12-28T on the back - question is - will I need to shorten the chain if I do this?

Also the BB is Ultegra 6500 (Octalink) - is this something I can sort at home, or worth taking to LBS - I don't have the tools, worth getting tools to do and do it myself - or LBS job?

dubbs2009

P.S. Looking to replace the Ultegra 6500 with this Claris 2450 http://www.chainreactioncycles.com/shim ... prod109701 one - my understanding is that this should work ok

slowbike

as you're changing from a shortest path from 39-12 to 34-12 then you will probably have to take a couple of links out - rather depends what it looks like atm.

It looks like you do need tools to swap the kit - tbh, removing a crank is not something you have to do that often, so it can be as cheap/easy to get the LBS to do it for you, but if the tools are cheap enough or you have enough interest then get them and do it yourself.

dubbs2009

Slowbike wrote:

as you're changing from a shortest path from 39-12 to 34-12 then you will probably have to take a couple of links out - rather depends what it looks like atm.

It looks like you do need tools to swap the kit - tbh, removing a crank is not something you have to do that often, so it can be as cheap/easy to get the LBS to do it for you, but if the tools are cheap enough or you have enough interest then get them and do it yourself.

OK thanks - I am quite interested on how to do it to be honest - think the tools I need are:

http://www.chainreactioncycles.com/shim ... p-prod5728 - £4.99
http://www.chainreactioncycles.com/shim ... rp-prod671 - £16.99

I guess if I do it - I can the swap between the chainsets should I want too...

dubbs2009

Actually - just need this I think > http://www.probikekit.co.uk/bicycle-tools-and-maintenance-nc/park-tool-ccp-44-crank-puller-for-splined-cranks/10772301.html Dont need to remove the BB so - just need to remove the cranks from both sides and replace.

I assume the front mech will need to move down a bit - how can one tell if they need to remove chain links?

dubbs2009

Also - I have 9 speed cassette - the Claris 2450 is 8 speed chainset - is that OK?

arlowood

dubbs2009 wrote:

I assume the front mech will need to move down a bit - how can one tell if they need to remove chain links?

Use this link to calculate the required chainlength. Just input max front crank, max rear sprocket and chainstay length and away you go

http://www.epicidiot.com/sports/chain_l ... ulator.htm

dubbs2009 wrote:

Also - I have 9 speed cassette - the Claris 2450 is 8 speed chainset - is that OK?

Chainsets don't normally worry about how many sprockets are on the cassettes - so the 9/8 difference will be irrelevant

dubbs2009

arlowood wrote:

dubbs2009 wrote:

I assume the front mech will need to move down a bit - how can one tell if they need to remove chain links?

Use this link to calculate the required chainlength. Just input max front crank, max rear sprocket and chainstay length and away you go

http://www.epicidiot.com/sports/chain_l ... ulator.htm

dubbs2009 wrote:

Also - I have 9 speed cassette - the Claris 2450 is 8 speed chainset - is that OK?

Chainsets don't normally worry about how many sprockets are on the cassettes - so the 9/8 difference will be irrelevant

Fab // thanks!

rafletcher

Slowbike wrote:

as you're changing from a shortest path from 39-12 to 34-12 then you will probably have to take a couple of links out - rather depends what it looks like atm.

Not necessarily. The governing factor will be the longest chain required - so look at the big-big ie 50/28 and make sure that's the right length. At most you'll need to remove 1 complete link (assuming you're chain is correctly sized to start with)

slowbike

rafletcher wrote:

Slowbike wrote:

as you're changing from a shortest path from 39-12 to 34-12 then you will probably have to take a couple of links out - rather depends what it looks like atm.

Not necessarily.

That's why I said probably ...

rafletcher wrote:

The governing factor will be the longest chain required - so look at the big-big ie 50/28 and make sure that's the right length. At most you'll need to remove 1 complete link (assuming you're chain is correctly sized to start with)

I tend to look at the shortest path as this is when the rear mech starts folding over on itself and you get chain on chain rub, but yes, you're right - the longest path is the way it should be measured.

964cup

Simplest way to set the chain length is to run the chain over the big ring at each end, but not through the derailleur. Bring the chain together, identify the link where it meets, add two links from there and hey presto.