I've recently been through a similar process, by fitting 235/55R18 tyres on Amarok rims on my new 4-motion T6.1.
While numerous people mentioned that this size tyre fit in the standard wheel carrier with the carrier set on lowest setting, we couldnt do it, even with the tyre deflated.
Without resorting to expensive Siekel carriers, I leant on a family friend who is a custom coachbuilder/panelbeater, and I'm pleased with the results.
We inserted shaped steel 25mm band at the front of the carrier, as per others on this thread.
View attachment 199437
Then, with some 25mm cut pipe as spacers at the front of the carrier, we were able to use the original bolts - longer bolts not required. The fitment of the bolts at the front does need some leverage from long screwdriver to bring the front of the carrier inline with the bolt holes.
We were able to use the factory bolt, noting that i'll replace the captive bolt (shorter thread) with a longer full thread version so both bolts have full thread engagement.
As a result, we didnt have to trim any of the plastic liner (those Siekel instructions to cut off the chassis bracket and then trim the plastic are shocking to me for such an expensive solution) and the tyre fits neatly in the slot - earlier it was a long way from fitting.
View attachment 199436
Very happy with the result. The carrier sits maybe 25mm below the rear diff housing, and the rear approach angle not quite what it was, but its a good outcome for minimal cash.