Could someone explain to me what is the purpose/use of A-3151 (blue UAZ)? Despite having a bigger tires it stucks in mud way more often than A-469 (green UAZ). It is slower as well and it struggles to drive over fallen trees. It's certainly not fun to drive. As for vehicle obtainable after some progression points I would have been expecting it to be much better.
its the old IRL wide vs narrow tyres problem.
wide tyres are good on bottomless mud, where to sink needs to be avoided, however the problem arises of directional stability on side slopes and lack of fundamental "frictional grip", but they still fall short of flotation tyres.
note: wide tyres and flotation tyres are not the same thing, with the latter being wider still and able to support the vehicle weigh at a much reduced tyre pressure.
narrow tyres are good where there is harder underlying ground (with mud on-top, or the mud is of the nature it is compressible), as when the tyre sinks it grips on the harder underlying ground and because the tyre is narrow it offers less resistance as it creates a wheel-rut.
something else to consider, is when you raise suspension height, unless your very careful, while you gain upward wheel travel, you tend to lose downward travel on the opposing wheel, which is the often forgotten part of what makes good suspension on uneven ground, as it is what keeps the opposing wheel in contact with the ground thus generating grip while the other wheel is rising over the bump/obstacle.
now if the task at hand was to carry 5 people and some cargo, then the A-3151 would probably be better than the A-469, as the A-3151 would sit lower on it suspension (thus gain downward wheel travel) and its tyres for its given mass would behave more like a narrower tyre and would conform more easily around rocks and branches.
the above is assuming ST mudrunner is using some of the real-world axiom of tyre, suspension, mass and mud physics.
afaik in the old spintires there was an "interesting" behavior where light tires would sink more than heavy tires and im not sure this has been fixed in this game. it was "fixed" by the mod spintires plus, tho.
there were also other "interesting" behaviors like this one but i cant recall them.