On the rear, there's only about one finger width between strut and inside of tyre ... so that's about 20mm at best. I am guessing that putting on a 255/55 would use up 5mm of that 20mm?? Is that likely to be a problem? Also on the rear, there is about 3cm (not 3mm) laterally from inside of tyre to the wheel arch trim. Not sure what might happen if this is reduced to, say 25mm by fitting 255/55's, and then bouncing around on rough ground. Or am I imagining a non-issue? Yeah, but were you not one of the first Gen 2 owners? I'm just a 'Johnny come lately' with just over 20,000km on these tyres (but wearing far too quickly IMO) ... so I am looking to the likes of you to lead the way. My wife drives ours most locally its just craked 30k after 2 years, the Tyres should be fine, just find a dealer willing to do a test fit and you should be fine, sounds like theirs enough room from your measurements