MTB Crankset Upgrade - Chainline and O.L.D. confusion

Equipment
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I recently bought a Orbea Occam H30 2022 which came with Orbea OEM 175mm cranks. In the reviews of the bike I saw they were widely panned as something needing an instant upgrade, and I agree from the initial user experience. I’m looking at Shimano SLX / XT 165mm or 170mm, which could also accommodate a power meter at some stage in the future.

However, I am confused about the spec around chainline and O.L.D. and wondering if someone can help before I buy the wrong thing… According to the spec above on the Orbea website the bike has a boost spacing crankset with 148mm boost rear axle. Can I use this? Shimano SLX M7120 Crankset without Chainring | ProBikeKit UK Do I need to get a ruler and measure my chainline or will I find it specified somewhere in the documentation? Thanks for any guidance!

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Looks like that is a Prowheel MPX11 / TFHPC ; uses SRAM mount rings; probably a 52mm chainline / 175mm q-factor; should weigh 810gr with rings. There’s nothing wrong with those arms.
2021 170mm Orbea branded Crankset For Sale 2021 Orbea OC1 Alloy forged Boost cranks 32t 170mm For Sale
TFHPC MPX11 24 mm 11s Crankset, Black | Bikeinn

So that’s a steel ring, so it probably weighs 125gr, so the arms weigh 685gr-ish.
Shimano SLX/XT direct mount would be 525gr for the arms and an after market ring would be 50gr or stock would be 115gr.

If you’re going with shorter cranks, then I’d go with a Shimano SLX or XT (same thing) with direct mount rings like you’ve got linked. The stock crank is probably closer to the narrower M7100, but the M7120 works too. M7120 should work great and would be better if you’re on flatter roads because the chainline favors the smaller cogs, but you’re getting a wider q factor. If you want to try to get a narrower q-factor the M7100 should work well too.

Don’t forget the ring- Shimano SLX M7100/M7130 Single Chainring - 12 Speed | ProBikeKit UK (it says 7100 / 7130, but shimano calls out the same ring ISMCRM75A2 )
And this one might be cheaper if you’re staying 175mm Shimano SLX M7100 Single 12 Speed Chainset With Chainring | Merlin Cycles

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Thanks for the reply. I wasn’t trying to call into question the quality of the OEM cranks, it was more the length of the cranks. I’m used to 170mm on my road and gravel bike, even with the higher bottom bracket I feel I’m knocking on a lot of things.

So the thing I’m taking from your info is that there’s not necessarily a ‘correct’ answer here, but it depends on function and there’s several things that would work?

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I went through this a few months ago. It’s a pain. 52mm of chainline should clear a pretty wide tire. 55mm chainline is for wide tire, big chainring, full suspension bikes that need more room by the chainstay. If you need to push out the chainring a bit, you should be able to do that with the normal crank and some spacers.

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