Cheers Richard, saves me wondering and/or having to 'experiment' too !

I have used my slim (235) spare a few times (due to slow punchures via beading leaks) and could not feel much difference compared to the 255s
... but did not 'push it' too far though either

Had lots of discussions with tyre folks over the years about fitting 'oversized' wheels because 'they look good'....
and whereby "Low Profile" equates to 'and you will feel every bump on the road' too !!

When I first got the SE, which was on the 18 x 8 wheels, I commented in my local LR independent that the ride seemed harder. The comment was, you want 18" for looks and 16" for comfort.

It's a factor, I'm sure but my jeep is on 235/75r15 and rides much stiffer than the Duchess on 255/55r18. If I had a criticism of the P38 setup it would be that the roll bars are way too soft but that could be a compromise due to the variable ride height.