My P38 has been wearing some 19" L320 wheels for the past 5 years, shod with 255/50r19 Michelin Pilot Sport 4's. Obviously a full "on road" high performance tyre. but not so suited for off road use.

I've decided to change things up a bit, so i've bought a set of 18" L322 "twin spoke" wheels (https://www.landyzone.co.uk/attachments/img_1080-medium-jpg.43591/) and was on the hunt for some all terrains. I also wanted to go up a little to a 30" tyre rather than a 29". 255/60r18 would have been the original fitment on these wheels on the L322, and measures in at 30", so i decided on that size.

I decided after much searching, on a set of Continental Cross Contact LX2's, in 255/60r18. Mostly because i managed to find a used set for sensible money (bit over £200 for a pair with 7.5mm and a pair with 6mm). I initially wanted something a little more aggressive like the Michelin Latitude Cross, but i couldnt find any. I was also looking at the likes of the Grabber AT3 and Toyo Open Country AT's but i felt on balance it was probably still going to see a lot of road miles. And i also couldnt find any of those used either. On reflection, this tyre size is a bit niche/rare. I would probably have been better going with 265/60r18.

Anyway thats the back story. The tyres got fitted to the wheels midweek and i set about fitting them today. When i removed the first wheel from the car something immediately struck me, the tread on the Continentals was much narrower than the Michelins.

So much so, I went and got a tape measure...

The 255/50r19 Michelin measured about 240mm across the tread,
The 255/60r18 Continental measured about 210mm.

For reference i then measured a couple other set of tyres that happened to be nearby:

255/45r20 measured about 240mm (and these are also Continentals, but a road tyre)
235/55r19 measured about 210mm (winters)
235/40r18 measured about 210mm (Goodyear Eagle F1's)

So the continentals are certainly the odd one out here, despite claiming to be a "255" they're measuring up like a ~235 tyre.

Anyone else seen anything like this? Anyone fancy sticking a tape over their 255's to get some more data points here?

Not really sure what i can do about it at his point ofcourse, short of spending even more money buying some other tyres. But i'm intrigued to see if this is a particular quirk of these Continentals or maybe an "all terrain" thing?

It does seem a bit odd. 255 is, or should be, the width in millimetres so that is what they all should be, although looking here https://tiresize.com/calculator/, the width doesn't appear to be the tread width but the sidewall width at their widest point. The red one I've recently got has 255/55 x 19 Goodyear Wranglers on it and the tread width on those measures 250mm but the sidewalls don't 'bulge' out beyond the tread by much at all and at the widest point would be around 255mm.

My car is on 7" x 16" wheels with 235/70 x 16 Kleber all season tyres, (which is usually a Disco or base model P38 size and that was what plod specified when it was new) and they measure around 210mm across the tread but 235mm at the widest point of the sidewall.

You probably thought this all through, but for me the 2 reasons why I haven’t (and probably won’t?) go with any larger tyres are 1, I’m worried about the bump stops allowing the top of the tyre to rub, and 2, it seems that you can’t fit even a marginally larger tyre in the boot compartment. (With our All Wheel Drive and viscous couplings, I think it’s quite important to have the same sized spare).

Indeed, For a more aggressive offroad setup i'd want to go larger 31-32" sort of range, and i had seriously considered some 255/70r18's from the new defender which are about 32", but once you get that far, there are certainly repercussions for EAS. I've seen folk recommend carrying some 2x4 offcuts to pack the bumpstops with in case of emergency, as the car wont roll on the bump stops.

The 30" tyre however isnt an issue at all. Its pretty much bolt on. Infact the rear was sat on the bump stops while i was installing them as the car was parked on a slope and it had let all the air out trying to level itself. Plenty of room.

My spare wheel well is filled with an LPG tank, so thats not really a consideration, though i have read slightly larger tyres will fit (sometimes only once deflated).

Gilbertd wrote:

It does seem a bit odd. 255 is, or should be, the width in millimetres so that is what they all should be, although looking here https://tiresize.com/calculator/, the width doesn't appear to be the tread width but the sidewall width at their widest point. The red one I've recently got has 255/55 x 19 Goodyear Wranglers on it and the tread width on those measures 250mm but the sidewalls don't 'bulge' out beyond the tread by much at all and at the widest point would be around 255mm.

My car is on 7" x 16" wheels with 235/70 x 16 Kleber all season tyres, (which is usually a Disco or base model P38 size and that was what plod specified when it was new) and they measure around 210mm across the tread but 235mm at the widest point of the sidewall.

I'll try and measure the sidewalls, but that could well be it. Still a bit crap that these tyres pinch in so much giving you much less tread on the ground.