I understand that when using gears you shouldn't use the smallest ring with the smallest cassette cog, and the largest ring with the largest cassette cog as it will cause the chain to wear more quickly due to having a less that straight chain line.

Does this also affect 1x9 set ups - i.e. does the chain / cogs wear faster due to cross chaining?

Thanks

Daven

depends on the chainline of the front ring

I had to try a couple of different BB spindle lengths to get my front ring centered on the cassette. But now that it is my chainline never gets more severe than my 2x10 when I'm in the small front and 3rd smallest rear.

Yes, but by definition you can't "cross-chain" with a 1x set up.

Chain's don't know or care which sprockets they're on, but they do care about alignment, and running on less aligned combinations will cause faster wear than on more aligned combinations. So looking at any bike with a multi-gear cassette, wear will be least on the sprocket that best aligns with the chainring, and increase as you move to those on either side of it.

With multiple chainrings the situation is similar, and while folks make a big deal about cross chaining, a quick sketch will show that using the outer with the 2nd innermost involves about the same chain angle as the outer/outer combination.

Cross chain issues aren't digital as in OK/not OK, but progressive, and best, great, good, poor, & terrible.

a chainline in between 4th and 5th on the cassette is what you need.
That's the middle of the cluster..

true enough, though the 5th sprocket is the exact center of 9. Between 4th and 5th is the center of 8.

In any case it doesn't answer the OP's question.

I ran a 1x10 using a 44t chainring on the inside position on a Sram GXP crankset with a Shimano 12-27 ten speed cassette. The chainring was inline with the 5th cog. It ran very well and provided better chain durability than my 2x10 or 3x10 bikes.