Wide Range Cassette: Derailleur Cage and Chain Length

[MudLark]

Hi guys,

 

My bike - a Trek Superfly 8 FS AL - came standard with 2x10 with 38/24 chain rings and 11-36 at the back coupled with an XT Deore SGS (long cage) derailleur. The standard factory chain is 111 links + the power link.

 

Not long ago, my bike shop replaced the derailleur with an GS (medium cage). They couldn't get the original derailleur to shift properly (the cage was a little bent) and only had the GS unit to hand. No problem, it all seemed to work fine with the standard setup even though the stated capacity of the GS (I read 33*) is exceeded by the OEM setup (39).

 

For reasons I'll explain another time, I have switched to a Praxis wide range cassette which is 11- 40. It works fine – in fact great – except if you make the mistake of using the 38 chainring together with the 40 cog – in which case it will climb on and work fine but you cannot get it to climb down again without first switching to the 24 chainring. Okay, I accept that one should not cross chain anyway but let's agree that sometimes "life happens". The reason it won't climb down is the angle of the cage becomes too severe, with the result that the metal of the cage actually overlaps the cog teeth and prevents it climbing down again (a close understanding of the exact shape of the cage at the pivot point would help an appreciation of exactly what the issue is). In substance however, what it seems to come down to is that the chain is a little too short for the "big – big" combination.

 

As the chain worked fine with the 11 – 36 cassette, I am assuming that if I use a chain four links longer (to accommodate the difference between 36 and 40) that that should give me a workable chain length. Would I be correct in that assumption?

 

The other thing is that the medium cage (GS) derailleur seems to be maxed out on the B stop and cannot take up any more chain length. I am assuming that if I switch to an SGS (long cage) derailleur, that this will take up the extra four links? The total Shimano stated capacity for the SGS as I have it is 46*, whereas the maximum I need in context is 43. Would I be correct in this assumption too?

 

* Source here: https://guides.wiggle.co.uk/rear-derailleurs-buying-guide

 

All useful input gratefully received...

[DieselnDust]

if you make the chain long enough for a 38 - 40 combo it make be too long for the 38-11 combo meaning you cannot use that gear.

Best option is to replace the GS cage with a SGS cage or long cage derailleur

[popcorn_skollie]

For starters your initial 'error' in using your big front ring with your granny out back makes me wonder why you're not just running a 1x drivetrain to begin with. 

[MudLark]

For starters your initial 'error' in using your big front ring with your granny out back makes me wonder why you're not just running a 1x drivetrain to begin with. 

 

I'm quite happy with the 2x10 at the moment - its what I know.. :-) I might eventually get to 1x11 but probably on a completely different (and better bike).

 

I could just forget the whole thing and follow proper discipline and avoid cross-chaining. But you know... :-)

[MudLark]

if you make the chain long enough for a 38 - 40 combo it make be too long for the 38-11 combo meaning you cannot use that gear.

Best option is to replace the GS cage with a SGS cage or long cage derailleur

 

 

Okay, thanks for that. That's what I thought might happen.

[HeyYou]

THis is what you need and a slightly longer chain

 

https://www.tomtop.com/p-y6403b.html?currency=ZAR&Warehouse=CN&aid=gplazacd&mid=10000016508&utm_source=SEM&utm_medium=Google+PLA&utm_campaign=TT_PLA_ZA_CD&utm_content=3707&gclid=Cj0KCQjwv-DaBRCcARIsAI9sba-97RmkANdQCYT7A-G6rKd1ZkenuTebIb6fncIP0Y7FzS6V0H7QjpQaAkIPEALw_wcB

[MudLark]

THis is what you need and a slightly longer chain

 

https://www.tomtop.com/p-y6403b.html?currency=ZAR&Warehouse=CN&aid=gplazacd&mid=10000016508&utm_source=SEM&utm_medium=Google+PLA&utm_campaign=TT_PLA_ZA_CD&utm_content=3707&gclid=Cj0KCQjwv-DaBRCcARIsAI9sba-97RmkANdQCYT7A-G6rKd1ZkenuTebIb6fncIP0Y7FzS6V0H7QjpQaAkIPEALw_wcB

 

Thank you. I wasn't even aware of that option. I read on the Evobikes site for the Wolftooth version that with an 11-40 cassette it only works if the chainrings have a maximum difference of 10 teeth... and mine has 14. So, the SGS derailleur it looks like it will have to be then.

 

https://www.evobikes.co.za/components/wolftooth-roadlink-10-11spd.html

[DieselnDust]

That's good but do consider that derailleur hanger extensions make the derailleursystem more susceptible to shifting inaccuracies as those components tend to bend more easily if impacted

[MudLark]

Okay, many thanks guys. I'm going with the longer derailleur and chain.

[droo]

A side note - the B screw isn't for taking up tension in the chain, it's for setting the distance between the guide pulley and sprocket to optimise shifting.