Disco 2 Urgent votes needed - D2 tyre choice between...

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Byeway
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A green lane in other words, not Off road, but on a rough old road!
You wouldn't be going fishing in them, hopefully!
You won't regret the BFGs.

I am looking into buying these https://www.landyzone.co.uk/land-rover/bfg-ko2-all-terrain.357914/#post-4815082.
I have 18" rims, those are 17"s (I would quite like more rubber and less rim). I am new to this, never heard of spigot rings etc. I see they will fit my vehicle fine, but not sure whether it will make any changes to speedo or any other noticeable differences like driving/handling etc. It's a manual so hopefully it won't screw up gearing, but grateful for any input on what I might need to consider if I switched to those.