That's a decision for when I can afford to swap out all four tyres, hopefully for all terrains. Would 255/70 fit the same rim too?

You'd probably not want to go any wider than a 245/70R16 on a 16" rim to be honest, and it wouldn't be an approved size for the rims depending on the actual rim width. 245/70 is a good enough fit to have clearance of bodywork and other vehicle parts without having to do a lift or cut body work. It's also not far off the OE size.
But don't forget, the '70' is the percentage of the overall width of the tyre. So the aspect ratio or 'profile of a 235/70r16 is actually smaller than a 245/70r16, by around 7mm. Doesn't sound a lot, but even that could cause issues with transmission.
 
That's a decision for when I can afford to swap out all four tyres, hopefully for all terrains. Would 255/70 fit the same rim too?

EDIT: or maybe not 70, as that's a % isn't it. Would want to keep the same rolling diameter.
The Disco will happily run on slightly taller tyres no problem. I wouldn't worry about going a bit bigger. A few mm overall in diameter will not make a huge difference IMO.
 
Just put some 235 or 245 70 16s on, job done. Ditch the 18s. 255 65 16 have poor choice of tyre if you want something chunky. Mixing 16s and 18s is ridiculous! As has been said.
 
Good discussion which obviously interests me at the mo. OP - I would be interested to hear what you did in the end, what you're running now, and what you think of the handling. I am about to change my 255/55/18 for 16" rims (7J i think, not arrived yet). I was going to go for the 235/70/16 (I like to keep to standard specs) but I am now thinking of going for 255/65/16 which are the same diameter but with a bit more width. Having only ever experienced the 18" wheels/tyres on the two D2's i have owned, I am curious to konw what differences (on the road) are noticed (if any) between 235/70 and 255/65. I would guess the wider tread would mean a bit less fuel economy but a bit more grip especially in the wet. But just guessing, hence why I found your thread. Hoping you might have some feedback which could help me decide?
 
I bought the five 16" rims and 235/70 R16 tyres, and when I took a look at them myself I couldn't really see any of the deterioration that the eBay listing mentioned (and the recent MOT mentioned nothing either, so I guess they were being excessively choosy to cover themselves) so I went ahead and swapped out all five.
Honestly I've not really noticed a difference, though I haven't actually driven that much on them. The traction control has maybe kicked in a little more often, bumps maybe feel a little smoother, and cornering a bit looser. But nothing I could really quantify, or say for sure isn't just in my head.
 
i moved from 255/55R19 to 255/65R16 and noticed a much softer, pliable ride and handling. I've also got a speedo thats legal!
 

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