I’m currently running a 3×9 setup, however having issues with gears slipping. They aren’t happy in the last 3 or 4 gears at the back, and just skip if any power is put down, it also has a habit of spitting the chain off when in the big ring up front.
A lad who I was riding with today reckoned a new cassette and chain would solve this? (Though I’m fairly sure there really aren’t That many miles on the current ones…?) He also suggested running a 2×9 setup with a bash, which sounds tempting as I don’t really use the big ring much and he reckoned it would improve shifting… But I’m not really sure how?

(I hope this rambling makes sense, a late night followed by a days riding/ driving has started to take its toll)

TL;DR: how do I stop my gears slipping? And what would I gain from 2×9?

Going 2×10 doesn’t make a bit of difference to shifting. Unless you plan on bashing into rocks then dont bother with a bash guard. How long in inches are 12 chain links? Measure in inches so will be 12″ or just over. Presumably rear mech is ok? Just replaced my rear mech as the spring was shot and there was play in it. Caused ghost shifting in the lower gears but not the uppers. Perhaps something with the spring load I’m not sure. Is your mech hanger straight? Cable lubed and tight etc?

Thanks for the reply!

The chain is about half a chain pins length longer than 12 inches, is that stretched enough to cause issues? I think the mech is ok, the shift seems pretty crisp, just doesn’t stay in when power is put down! Hanger looks to be straight too.

After closer inspection, my big ring is fairly f***** which explains why it wouldn’t stay in that gear.

After all this (and with the prospect of riding a LOT more this year) I’m considering splashing out and going to an external BB (Instead of the current octalink setup) with new BB, cranks, chain, cassette and potentially a medium cage mech if funds are still reasonable. Would that be all I need for a swap over to 2×9 with new cranks/ bb? Or would some sort of chain guide be required as well?

I doubt its your big ring wear.

(Though I’m fairly sure there really aren’t That many miles on the current ones…?)

Miles is not a proper/good measure of chain/gear wear in mountain biking.

If the big ring is mangled that would explain issues with that but not the rest. Check the gear tune on a stand if you can and look at where the mech sits in the gears.

When you say last 3/5 gears do you mean the big or small ones. If it’s the small it does sound like wear in there somewhere.

If your doing for a whole new setup I’d suggest 10 speed for forward compatibility. Something to retain the chain will help a bash does half the job quite easily and either a lower roller or clutch (type 2) rear mech does something similar. Also if you don’t use the big ring much a 10 speed setup will let you run a bigger couple of front rings (they go to more teeth at the back) so you gain more top end than running 22/32 probably 24-26/34-38 depending on you cadence and locality (Stressing that everyone is different and everyone rides different bikes in different places – 1 Size DOES NOT FIT ALL!)