Cybersled

What prevents the design of a super fast, lightweight tank?  It would rely on speed and manueverability, lack armor, and use rocket propelled grenades as weaponry.  It would rely on thrusters and propulsion instead of the standard tank track.  Could such as design exist and still have reliable fuel efficiency? 

What, like a hovercraft?

>>1
No, thrusters consume fuel like nobody's business. Plus, what you say in your first sentence is already the case. Tanks today are much smaller, faster, and more light weight than they used to be.

What about wheeled tank, but one that can move sideways or diagonal, like the spherical wheels in Dominion Tank Police?  The tread system seems merely "adequate."  Why not have a Batman Returns style wheeled tank, basically a dune buggy/ 4 wheeler for combat which would outmanuever conventional tanks and still have weaponry that can disable a tank.

>>4
These also exist. They are more often employed by national guard or big city swat forces. Problem with wheels is that wheels mean tires, and tires me flat tires.

>>5
Solid rubber tires work, they are very exspensive though.

Solid rubber tyres do not demonstrate adiquite wear characteristics with respect to belted type tyres.  Moreover, they lack the inherent damping qualities of a traditional tyre.  High frequency vibrations and peak loads will be transfered directly to the frame of the vehicle without a seriously overbuilt suspension.  This results in a considerably reduced fatigue life of structural materials.

If you think about it, this design already exists and has been deployed successfuly with a number of modern armies.  They call it they attack helicopter.

tracks make better contact with the ground than wheels do. I don't think there's a whole lot that can take out an american tank anyways, but I've heard the military may start favoring lighter quicker tanks to handle urban terrorist situations better