Any SRAM whisperers here? Cassette/chain issues.

I built up a Moxie MX3 frame I bought here in the classifieds, partly with bits from my old Scandal frame.

It’s SRAM GX drivetrain (now with XO1 derailleur, as my GX was getting tired), with an XG-1275 10-52 cassette, GX chain and 32 tooth GX chainring/crankset. When I first built it up, In was having a problem (never had on the Scandal before) with being unable to back pedal on the 52 tooth ring without throwing the chain off, landing several gears down the cassette. After a bit of research, I thought the problem was the standard boost 52mm chainline I used – Pipedream’s site says use 49mm unless running 34tooth oval boost setup. I’ve now dropped the chain line to 49mm and it still throws the chain off back pedalling on the 52 tooth ring.

The cassette is only 6 months old and had pretty light use in that time. I’ve tried a brand new chain with no difference. I can see no damage to the cassette. Nor anything wrong with the frame or rear wheel alignment.

The only other thought I had was I’m running a Nukeproof BB which doesn’t have the groove in it the SRAM Dub ones use for the 4.5mm spacer to slot into, so my chain line might actually be 50mm or 50.5mm or something like that. This seems too small to matter though and hasn’t affect my other bike running the same Nukeproof BB with SRAM bits.

Anyone got any ideas?

Oh and FWIW, I’ve read all the google results saying “nobody pedals backwards” and “1x systems are the devil’s work and designed to fail”.

But surely there’s a solution? Even going back to a 10-50 cassette maybe? The one on my other bike has no such issues.

I’d say its definitely a chainline issue and / or b-tension set incorrectly.

12-speed backpedal issues seem to be less common on frames that are natively 52mm chainline and above.

Have you lined it up using the SRAM B tension alignment tool? Is the chain 100% the correct length?

Also …

https://www.oneupcomponents.com/pages/understanding-chainline-for-optimal-1x-conversions-boost-and-non-boost#:~:text=Chainline%20is%20the%20distance%20between,you%20have%20multiple%20front%20chainrings.

Yes, the B-tension is spot on. In terms of length, maybe – I did the usual ‘wrap the chain round the biggest cog and chainring and add 4 links (for hardtail)’. This took me to the wrong link for the Powerlock, so as per the instructions I’ve read/watched, I added an extra link. So I’m at +5 links now.

Chainline plus b tension.

Bear with me. I’m running GX1 on 1×11 32t up front 42-10 at the back. But with a slightly compromised chainline due to using the Hope boost adapters.

It only JUST works. If the limits are correct and the tension good, there is about 1/4 turn of the b-tension where it will work. Add tension at that point and the chain will not drop, at all. Any less and it fouls it slightly so it won’t shift onto the big sprocket. It also needs the pivots of the mech to be well lubed so nothing impedes it.

12 speed is more of a faff still and is, I believe, right at the limit of what is practical for a normal Joe Public rider in terms of:

1. Time available to set things up perfectly.

2. Getting it covered in mud.

3. Money to keep replacing chains to keep it working.

If someone would bring out a 9 speed that did something like 46-11, I’d buy it like a shot.

freehub friction?

mattrockwell
Free Member

Yes, the B-tension is spot on. In terms of length, maybe – I did the usual ‘wrap the chain round the biggest cog and chainring and add 4 links (for hardtail)’.

TBH the best way is to ignore all that crap and just put your bike in the biggest cogs and cut to length. Does it look OK- ie is the mech stretched out super far, does it have a nice little bit of s bend in the chainline through the mech?

Thanks for the suggestions. I’m gonna tweak the chain line inwards a bit more to start with. They try shortening the chain a bit if that doesn’t work. I do wonder if the whole 52 tooth (it’s one more than Shimano, etc) is a bit daft. The GX setup with 50 tooth ring on my other bike works perfectly.

I do wonder if the whole 52 tooth (it’s one more than Shimano, etc) is a bit daft. The GX setup with 50 tooth ring on my other bike works perfectly.

TBH, I think it is probably this. Asking a single mech to cover that range with perfect gradations across 11 gaps is getting on for being an impossible ask. Particularly on a MTB that is being clattered around, caked in mud, back end growing/shortening if a FS etc.