NOTE:
Dont freak out if you see wheel colision out of position in some of these pics, its like that for animation purposes only.
Here is the low down.
Projectile angle is key to tank combat. Example below.
A direct hit at 90 degree angle will dish out 100% of its potental damage.
While a projectile hitting at a 45 degree angle will "deflect" and only dish out around 45-50% of its potental damage.
Now here is a some pics to help those find those key areas.
Leopard
T-55
T-84
Potental Damage
Note: Chart below is base on 100% potental projectile damage.
Blue: = 4 to critical Hp/5 to destroy
Green: = 3 to critical Hp/4 to destroy
Red: = 3 to critical Hp/4 to destroy
Teal: = 1 to critical hp/2 to destroy
Happy tank hunting.
I have re-uploaded the images from my HDD.

