LeeRoy said
If your mech weighs less than 100 tons then it's too short.
That depends. Not all mechs are bipeds. You still have hexapods and quadrupeds to consider, which have multiple legs and thus can spread their weight out more evenly, enabling them to pack on more armor (which constitutes more weight) yet retain a relatively short stature as compared to something like a mobile suit, an armored core or a run-of-the-mill battlemech.
Skallagrim said
LOL you are not thinking of advanced super materials nor nano-carbon fibers, trust me if the game makers actually knew material sciences they would make their mechs using these materials which are far more durable than normal metal alloys and much harder whilel reducing weight.
That's true, but you're still going to get boned by the square-cube law. Regardless of what junk you make your mech out of, your weight is going to increase the further you increase its size. Two-legs, for the most part, are absolute shit when it comes to handling that weight; if anything, most of your weight is going to come from the sheer mass of the reinforced endoframe and locomotive systems (either artificial muscles formed from CNTs/silicon, servomotors or hydraulic systems) that you're going to base your machine off of. The rest of your weight is going to be armor, and if you're going by realistic standards, it won't be much.
And thus, this is why MBTs are superior. Such a simple machine, with simple shapes, yet a low center of gravity, a psi less than a civilian car and a hard-hitting weapon that can easily be scaled up without having the tank nor the crew suffer from the recoil of such an armament.