On a double chainset (fc-m8000-b2) for boost frames and bikes, is it the chainset spindle itself that is slightly longer or are the chainrings dished to get the correct chainline? Just wandering if a normal NW single ring would fit and keep the correct chainline.

Thanks

On Shimano the spindle is longer so any chain ring will fit.

On Sram it’s the chainring is either boost or non boost.

Also remember M8000 has a specific BCD so you need an M8000 compatible ring (96mm bcd)

Thanks 🙂

The difference in offset is from the spider.

Crank arms, axle and rings are the same.

don’t automatically buy a boost crank, if you have a boost frame. The non-boost crank actually gives a better chainline, as long as the rings clear the chainstays. This is for 1x. 2x may have front mech issues too.

Never understood why the perfect chainline is right in the middle of the cluster, it’s not like the cogs are the same size. I prefer to shim the chainring as close to the chainstay as it will go, less crunch in the bigger cogs.

It’s even worse than that…. a chainline of 51mm doesn’t actually line up the chain the middle of the cassette. It’s actually further out that the middle sprocket. The middle of the cassette is more like a chainline of 47mm. I suspect they (manufacturers) set it at around 50mm so they don’t have rings hitting chainstays. The reality is that with small rings that we see today, on 1x, that this is less of an issue.

Boost frames actually have an advantage here, as if you fit a non-boost crank/ring then it brings the ring inboard by a few mil, and thus has a pretty good chainline.

Never understood why the perfect chainline is right in the middle of the cluster, it’s not like the cogs are the same size.

No, but the distance between the top of the chainring and the top of the sprocket is pretty much the same in all gears, so the distance over which the chain is being deflected is the same.

As reggiegasket says, the “standard” chainline is someone off centre.  On 11 speed it actually lines up with 8th gear rather than 6th.  Shifting is improved if you get it closer to centre, but depends on chainstay clearance and also the possibility of the chain catching on 10th gear when in 11th.