Does chain need shortening when changing chainset ??

Sportiveman

Hi
I going from a standard 52-39 chainset to a compact chainset 50-34 do I need to shorten the chain if so how many links? The front mech will need moving down as well is that correct? :!:

SME

If you're going from a 52 to a 50 on the large chainring (and from 39 to 34 on the smallest) then it is likely that you will need to remove one full link. On the inner chainring and the smallest rear cog the chain could be slack enough to droop and ride and /or bounce along the chainstay, so you'd have to check this - the rear deraileur may be 'sprung back' on itself a lot and not be able to hold tension on the chain properly.

If you remove a link be careful to check that on the largest chainring and largest rear cog that the chain isn't overstretched and the rear deraileur's cage isn't pulled too tight (pulled too far forward).

The front deraileur is normally set about 2-3mm above the teeth on the large chainring.

Matthewfalle

1. Yes. The chain will need to be shorter as your chainrings are smaller. Only you can tell this as you know what rear cassette you have and can see. Use it as an opportunity to fit a quick link.

2. Yes, you'll need to move the front mech down as the chainrings are smaller.

3. Check tyre clearance when doing this - when I did the opposite 9(e compact to normal) the reduced clearance meant that I can't run anything bigger than a 23 on the back.

Baron Ban Ana

Matthewfalle wrote:

1. Yes. The chain will need to be shorter as your chainrings are smaller. Only you can tell this as you know what rear cassette you have and can see. Use it as an opportunity to fit a quick link.

2. Yes, you'll need to move the front mech down as the chainrings are smaller.

3. Check tyre clearance when doing this - when I did the opposite 9(e compact to normal) the reduced clearance meant that I can't run anything bigger than a 23 on the back.

+1 for all of the above. I must have been lucky with point 3. I never even considered it but after looking, there is just enough space for 25mm tyres!

This video should help you out;

https://www.youtube.com/watch?v=ELsKrgTt0oYc" target="_blank

The wire coat hanger trick is quite cool, i just spent ages cursing when the chain continuously slipped through my fingers!!!

Sportiveman

Thanks for the advice guys, new chainset, bottom bracket and chain are fitted and shortened I'm still waiting for the preload cap thing to turn up and also my new fd before I can test it though

Moonbiker

Sorry im being dumb but how does it affect clearance l though chainline was a set standard value?

Is chainring size diffrence causing the problem or is it different crank bb altering chainline?

http://www.parktool.com/blog/repair-hel ... -section-2

now im confused after reading this though....

Sportiveman

Pre load cap is installed cranks fully installed now just do a sun dance to get some decent weather next weeks job install new ultrega fd :?: :? :!:

SME

Matthewfalle wrote:

1. Yes. The chain will need to be shorter as your chainrings are smaller. Only you can tell this as you know what rear cassette you have and can see. Use it as an opportunity to fit a quick link.

2. Yes, you'll need to move the front mech down as the chainrings are smaller.

3. Check tyre clearance when doing this - when I did the opposite 9(e compact to normal) the reduced clearance meant that I can't run anything bigger than a 23 on the back.

I'm curious about point 3 as well. Never had a problem. ???

Matthewfalle

If you go and look at your bike now you will see a gap between the rear wheel and the seat tube.

The front mech band will also sit on the lower end of the seat tube - if it's a compact chai set, because the 'rings are small, it will be quite low down.

If you fit bigger 'rings, obviously you have to move the front mech up to clear them and for the mech to be able to shift the chain over the 'rings.

This will bring the mech into a new position that, if the bike was originally a compact bike, will fill a previously small gap between rear tyre and seat tube.

You may get away with it and there will still be clearance but on my bike it meant tyre rub in anything over 23mm and even then, dependent on what tyre used, slight rub then.

So I got a Dremel out and ground a section of the rear mech band off and then painted it black (all in situ) so you can't tell.

9 years on all is still well, however I still run 23s.

If I get around to it I'll take a piccie, but hey, you know what I'm like.

HTH.