Hi, very rare I post, but a read an awful lot
Great forum

My question being – what chain length would be ideal for this setup :

38t single front ring
11-34t cassette
Sram x0 medium cage rear
Kmc ti chain

It’s on my hard tail
Mainly ride the red route at pines, Cannock ect….
Like the faster down hill sections, but recently the chain keeps jumping off the front
Run a hope top guide with a mesh bottom roller

I’m looking for a definitive answer if poss

Many thanks
Tom

how long is your chainstay? the length of this will make a difference to chain length..

As long as a piece of string…

Impossible to say with out having the bike. Put chain on big cog and big chainring without running it through the rear mech and add two links.

Put chain on big cog and big chainring without running it through the rear mech and add two links.

^^ this long…

chain jumping off a single ring with no front mech or other device to hold it on ? – not down to length IMO

You prob should consider at least one of:

chainring with variable width of teeth – or at least a SS chainring
rear mech with a clutch doodah (maybe yours already has ?)
retention device (or even just bashring one side and a keeper ring or jumpstop on the inside)

Scaredypants chain jumping off a single ring with no front mech or other device to hold it on ? – not down to length IMO

I run a hope chain device and a mesh bottom roller tensioner as posted in my original post

Bikeneil – thank you for your response, I’ll try this setup tomorrow and compare how it is now

Rootes1 – I will measure tomorrow…..thanks

The hope chain device runs in conjunction with a hope bashring also

Can you post up a pic of the setup in the biggest gear at the back (largest cog, not highest gear). Let’s see the angle of your dangle, and we can then guess whether you can lose another pair of links.

Rootes1 – I will measure tomorrow…..thanks

no need was just trying to point out that despite you post other info you missed that is relevent.

best as above Big- big plis 2 links (and that is is 2 full link so 2″ – before you cut check that the rear mech is ok in at both ends of the cassette and also don’t forget to allow for the quicklink

Not the best picture

If that’s big cog at the back and a single ring front you can lose at least one pair of links (inner and outer) and maybe two pairs. Mine on the big cog has the mech cage fully extended forward

I run a hope chain device and a mesh bottom roller tensioner as posted in my original post

😳

Still, if chain/ring is “secured” correctly at top & bottom it shouldn’t be possible to ship the chain from the front – should it ? Is the tension spring(s) OK in the mech ? Do you back-pedal a lot to rearrange your feet for corners ?

(looks to me like you could get a couple of links out of that, but I don’t use SRAM mechs. What cog at the back do you use when descending ? if it’s a small one, your chain will still have slack in it)

Definitely one full link if not two full links fewer would be better.

Thank you for all the input, I’ve removed 3 links – it’s allot better
I think I’ve found the route of my problem, my derailleur has become weak, the springs are soft all of a sudden, gonna swap it for anther sram xo if it arrives tomorrow

Thanks once again
Tom