Ludite mode is ON.

Is the primary advantage of a thick thin ring the fact that you can get away without using a chain guide?

If not have I missed something more obvious?

Ludite mode is OFF.

No, that’s it.

Yup, though you should really use them in conjunction with clutch mechs.

An upper guide is also still a good idea if you ride really rough stuff.

Why the need for a clutch rear derailleur?

Why the need for a clutch rear derailleur?

to give the chain permanent tension so it doesn’t fall off

An upper guide is also still a good idea if you ride really rough stuff. race for a living

What he said. Basically a thick/thin chainring reduces the chance of losing your chain, as do upper guides and clutch mechs. On their own though, the first two individually will not usually be reliable enough.

A combination of thick/thin and clutch mech usually removes any need for the guide.

Clutch mech increases “effective” chain tension, whilst still allowing chain to shift, to stop excessive chain flap.

Thick/Thin profiled chainrings stop excessive side-to-side movement of chain on the chainring, by creating a tighter fit of the chain links onto the teeth of the chainring, whilst still allowing enough side-to-side movement so that the chain can reach all cogs on the cassette.

Both help to stop the chain coming off. Whether both are necessary depends how bumpy it is.

Oddly enough, I run a clutch mech and normal chainring with no guide. I rarely lose my chain but when I do it’s on smooth/rolling bumps, not the rocky/rooty trails where I would expect to lose it.

HoratioHufnagel – Member

Thick/Thin profiled chainrings stop excessive side-to-side movement of chain on the chainring, by creating a tighter fit of the chain links onto the teeth of the chainring

Have often wondered – that tighter fit must have an effect – it must mean more friction, as it will be harder for the chain to slide on and off the teeth as you pedal. I’m guessing it’s not significant.

It’s not really a tighter fit – it’s just filling up a gap that is normally just air – same as on the thin links.