Sharp front edges are good for mud... but no good at all for rocks. If you want traction on rocks you want smooth front edges...
I used to take the angle grinder to new tyres to take a big whack of the front edge off (for rock crawling comps... sticky compound, 40" tyres). They hook up significantly better on the rocks if you get rid of the front edges. Used to be a major smoke show coming out of my garage when I got a new tyre... I tried using a tyre groover, then a heated knife, but ended up with a grinder - works a treat.
Take a look a couple of years back when Dave won Tuff Truck on an old set of sticky BFG's... they were crazy worn, all the way down to having bits of belt showing. But they hooked up amazing on the rocks...
Big lugs chunk. Big hard lugs chunk even more. Coopers are a pretty hard compound... that's why they claim such high milage.
S.
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