Chain length with change of chain set

dee4life2005

I'm helping my mate swap his 53/39 chain set to a 50/34 and his rear cassette from 11/25 to 11/28. Anyone know if we'll need to shorten the chain at all for this ?

nicklouse

Well you will be using a new chain won't you? So just size it correctly.

dee4life2005

It's a brand new bike ... Was a good deal on the double version of the bike, which even after factoring in buying the compact chain set for it it still saved him about £150, so it's a new chain anyway.
I would normally size it properly, but alas my topeak chain breaker snapped in two a while back and I never got round to getting another yet ... Just wonder if I'll need to get one before I give him a hand, as he's quite eager to get out on his new bike.

Terrytibbs

I think it should just about be ok. Not completely certain though. I'd just swap it and try it check it's not too loose and too tight the highest and lowest gears.

drlodge

I would think you'd need to take a couple of links out. With the chain on the small chainring and sallest sprocket the rear derailleur should just be under tension.

On the original setup you have 39-11, the new setup is 34-11, that's 5 teeth difference. 50/34 with 11/28 will max out the RD cage so I would check the chain length in both the 34-11 and 50-28 positions before deciding on length. You may get away with removing 2 full links, or may need 3 depending on how the length is currently.

keef66

Depends how short it is at the moment really. My guess would be the smaller big chainring and the larger biggest sprocket would mean the chain is probably going to be the correct length.

Fit the new chainset and cassette and try it carefully on the workstand. If it runs happily in the big-big and small-small combos then Robert's your relative.

In those extremes it should be obvious if it's loo long or too short.

MichaelW

See here.

dgunthor

put it on the big chainring at the front and the largest sprocket at the back - rear mech shoudln't be ridiculously stretched and the chain should turn

put it on the small chainring at the front and the smallest sprocket at the back, rear mech needs to take up all the slack

drlodge

As above - I always size the chain length on small-small, then double check there's enough length large-large.

On the orignal setup, there's a fair but of leeway on chain length, but on the new setup there's very little, if any at all.

lesfirth

By my reckoning your chain will be Ok on your new set up.

You are going 3 teeth smaller on the front and three bigger on the back , so big to big is the same. Your chain will not be too short. You are unlikely to use 34 and 11 so it does not matter if its a bit slack .

If your chain is too short on big to big you can have a disaster. If its too long on small to small your chain will rub on its self at the jockey wheels, that is no problem ,it wont cause a disaster.

drlodge

lesfirth wrote:

By my reckoning your chain will be Ok on your new set up.

You are going 3 teeth smaller on the front and three bigger on the back , so big to big is the same. Your chain will not be too short. You are unlikely to use 34 and 11 so it does not matter if its a bit slack .

True that big-big is the same, so it won't be too short. But small-small is 5 teeth less, thats more than just a bit. It really depends how the original chain length was setup as to whether it will be too long or not. The OP will find he will need to remove between 0 and 3 full links (0, 2, 4 or 6 teeth worth).

dee4life2005

I've also just found out that the bike has a braze-on front derailleur (105) ... I take it is still possible to switch from double to compact as I believe that a braze-on derailleur has no height adjustment ?

dee4life2005

drlodge wrote:

True that big-big is the same, so it won't be too short. But small-small is 5 teeth less, thats more than just a bit. It really depends how the original chain length was setup as to whether it will be too long or not. The OP will find he will need to remove between 0 and 3 full links (0, 2, 4 or 6 teeth worth).

okay, I`ll pop past the bike shop on the way home and pick up a new chain breaker and a couple of quick links just in case I need them then. Ta

drlodge

dee4life2005 wrote:

I've also just found out that the bike has a braze-on front derailleur (105) ... I take it is still possible to switch from double to compact as I believe that a braze-on derailleur has no height adjustment ?

Yes it does, or should. The "hole" should be more like a "slot" so adjustment of height is possible.

shmooster

Braze on does have height adjustment, there's 10mm or more (on the derailleur itself) so, plenty for what you need I expect.

drlodge

shmooster wrote:

There's 10mm or more (on the derailleur itself) so, plenty for what you need I expect.

What 'ya takin 'bout Willis? What adjustment on the FD itself?

Terrytibbs

drlodge wrote:

shmooster wrote:

There's 10mm or more (on the derailleur itself) so, plenty for what you need I expect.

What 'ya takin 'bout Willis? What adjustment on the FD itself?

He must mean on the front hanger, not the mech itself.

shmooster

Terrytibbs wrote:

drlodge wrote:

shmooster wrote:

There's 10mm or more (on the derailleur itself) so, plenty for what you need I expect.

What 'ya takin 'bout Willis? What adjustment on the FD itself?

He must mean on the front hanger, not the mech itself.

Yes, I meant where the derailleur mounts to the frame, sorry not looked at the thread for a while.