I do have to agree with the above poster. I primarily play as Engineer or a Recon and it is almost untenable to try to take a tank out of HQ and head for an objective. No tank on an objective will survive for long in the barrage of RPGs shoulder-fired or lock-on missiles.
I continue to play the game and I like it but the truth is everyone, and I do mean everyone, that I have seen take a vehicle of any kind onto an objective will lose that vehicle very, very quickly.
For example, and anti-armor engineer will carry five RPGs, and there is usually more than one anti-armor engineer on the scene. They can fire them about as quickly as every three seconds. The only choice is that the tank driver can run or be destroyed.
Personally, I survive by thinking of my tank as an armor-clad sniper with immense ranged attack power. And therefore, I do not attempt to enter an objective even though I would like to support my troops.
If I do enter an objective, the first thing that will happen is not that the enemy will shoot your friendly supporting troops, but they will instead first destroy your tank. So, holding an objective with the tank is a terrible idea.
In addition, one Recon guy with C4 is enough to destroy a tank. That seems like a pretty bad idea when you're on the receiving end of the C4.