Feanor

I believe the M6 variant extends the size of the hull, and replaces the engine. Also the T-90 is only 46.5 tons.

EDIT: I guess what I'm talking about is not upgrading it to the T-90 standard, but retrofitting T-90 components to a T-55M6. How well would this kind of configuration work for say third world countries seeking to upgrade their tank fleet, but short on money for new tanks.

Inst

What about the cost factor? The M1A2 costs about 4 million dollars. The T-90S was up for sale at 2 million a piece.

Is the present nature of Western MBTs an abnormal situation? Does the cost of an American life, in training, strategic, and political value, make it so that it begins to make sense to add excessive levels of armor during the design phase? How much does the protection and engine of an M1A2 cost anyways?

I know there's other factors involved, of course. One, tons of cheap crap dissipates your capacity for force concentration. Twice the numbers equals 4 times the combat effectiveness, but if they're engaging you in 1-on1 combat, then the firepower advantage is dulled and we go down to only twice the combat effectiveness. Two, the cost of fuel, of payrolls, of rations; this stays the same no matter how cheap the equipment. The apocryphal (or not apocryphal) Chinese human wave requires a several-fold superiority in a logistics train. Three, superior armor increases the effective engagement range. If you can penetrate his frontal armor at 2km, and he can only do so at 1km, the effectiveness becomes far greater. Four, a lower quantity means higher stealth. Every additional soldier or piece equipment means that your chance of evading detection has to be fractionally multiplied again.