Which would you choose

[SteveC]

Guys - see if you can answer this
My every day tyres Cooper ATR3 are 245/70/17, giving me actually 200 mm of surface tread that touches the tar
My new (yipee, don't tell the wife) are 265/70/17 and they also give just 200 mm of surface tread that touches the tar but are 265 at the side wall. What's with mud tyres having less surface?
Is that normal? If I had known I'd go to 285 wide...

[Dieselcon]

They should be 265mm in width and the height of 70% of 265mm.
Mmmmm. Did I read your post wrong?

[SteveC]

They should be 265mm in width and the height of 70% of 265mm.
Mmmmm. Did I read your post wrong?

You read right. The design of the KM2's gives less contact area it appears. They seem to have a more "rounded" edge thus less contact on the road.

[Wooders]

Steve, Where are you finding this contact area specification?
This would very with every different tread pattern, and the more agressive the tread pattern the bigger the voids between the tread blocks. So not surprisingly less rubber touching the grond (for the same size).
Also how is the contact patch measured since this would vary with different rim heights, tyre pressures, individual vehicles weight as well as the brands sidewall specifications - ie all the things that effect tyre bagging out....

[SteveC]

Wooders
Thanks for your input and valid points Dave
I measured across the tread with a tape measure. The At3 measure 200mm as does the KM2's from most outer tread block to other side even though one is 245 and the other 265. Yes the wheel width is 7.5" as opposed to 8" but that would have no affect on my measurements as would inflation unless really low as opposed high. . It looks like mud tyres have less contact area than a AT or H/T would have for the same tyre width dimensions, which I find odd really, well at least for the KM2's.
It would be interesting to know what others know of their tyres. For eg if you have 315mm tyres does that refer to width of the carcass or width of tread??
Any way I'm happy to have got them at a reasonable price after screwing them down a fair bit. I think!

[Paul-JK]

As far as I know the stated tyre width is the carcass width at the widest point of the tyre. I'd assume this this will usually be the side walls, although that could change slightly depending on width of the rims you've got them on and the tyre pressure. I'm guessing it will be measured at a "standard" pressure on "standard" rims but I've got no idea what those standards are. The tread width is always less than the stated tyre width but how much less depends on the tyre design. Can't help with muddies I'm affraid but for the 2 tyres that I've had the measurements were:

GY Wranglers; stated size 245/75/17; tread width 195mm
MT ATZ 4-Rib; stated size 285/70/17; tread width 240mm

[SteveC]

As far as I know the stated tyre width is the carcass width at the widest point of the tyre. I'd assume this this will usually be the side walls, although that could change slightly depending on width of the rims you've got them on and the tyre pressure. I'm guessing it will be measured at a "standard" pressure on "standard" rims but I've got no idea what those standards are. The tread width is always less than the stated tyre width but how much less depends on the tyre design. Can't help with muddies I'm affraid but for the 2 tyres that I've had the measurements were:

GY Wranglers; stated size 245/75/17; tread width 195mm
MT ATZ 4-Rib; stated size 285/70/17; tread width 240mm

Thanks Paul
Your measurements reflect much of what I have thought now. Interesting to see that your 285/70/17 is 240mm while my 265 is 200mm... yet only 20mm spec difference

BTW
If any one can help me, who have put after market wheels. (steelies in particular), how did you cover the front hub nut as in the image attached. The Dynamic wheels I bought don't supply full hubs for Jeep wheels due to the very close face I was told? so I'll need the sort of thing you see on trailers.
I don't want to get dirt inside if I can help it.

Thanks