What is a good armour for a tank supposed to strike from "afar" with an AC/10 or a Gauss Rifle?
I have in the works a light slow tank with a big gun and only 2.5 tons of armour. Is this enough or too light?
And before you mention it, I can explain everything through fluff 
If its intended to stand off and shoot forward, 15 front. (With no turret.)
With turret, and intended to get mixed in a bit more 10 to the front and sides.
Enough or too light is really a question concerning its total mass. Figure 10-20% mass devoted towards armor is normal.
Any amount of armor works if you want it to. I know many the long time old S7 users (Like the 3 of us assuming you are both the same people with those names from the old site) have built pretty much everything, so the fluff really become the defining feature.
It you are happy with the design as it pertains to your fluff, roll with it.
That said, I do think a tank should be able to take at least 1 or 2 decent hits on its armor.
Among my old designs I recently unearth, I found a tank that sounds similar to what you are going for. You can use it as a reference point if you want. (Production year was only set to 3098 to make my stuff easier to find in MegaMek. Filtering by year when my tanks were set to 3098 and Mechs to 3099 made it real easy.)
BattleTech Vehicle Technical Readout
VALIDATED
Type/Model: Armored Car Type D
Tech: Inner Sphere / 3098
Config: Wheeled Vehicle
Rules: Level 1, Standard design
Mass: 25 tons
Power Plant: 80 I.C.E.
Cruise Speed: 43.2 km/h
Maximum Speed: 64.8 km/h
Armor Type: Standard
Armament:
1 Autocannon/10
Manufacturer: (Unknown)
Location: (Unknown)
Communications System: (Unknown)
Targeting & Tracking System: (Unknown)
--------------------------------------------------------
Type/Model: Armored Car Type D
Mass: 25 tons
Equipment: Items Mass
Int. Struct.: 12 pts Standard 0 2.50
Engine: 80 I.C.E. 0 5.00
Cruise MP: 4
Flank MP: 6
Heat Sinks: 0 Single 0 .00
Cockpit & Controls: 0 1.50
Crew: 2 Members 0 .00
Armor Factor: 48 pts Standard 0 3.00
Internal Armor
Structure Value
Front: 3 23
Left / Right Sides: 3 10/10
Rear: 3 5
Weapons and Equipment Loc Heat Ammo Items Mass
--------------------------------------------------------
1 Autocannon/10 Front 0 10 2 13.00
--------------------------------------------------------
TOTALS: 0 2 25.00
Items & Tons Left: 8 .00
Calculated Factors:
Total Cost: 348,000 C-Bills
Battle Value 2: 301 (old BV = 200)
Cost per BV: 1,156.15
Weapon Value: 78 / 78 (Ratio = .26 / .26)
Damage Factors: SRDmg = 9; MRDmg = 5; LRDmg = 1
BattleForce2: MP: 4W, Armor/Structure: 0 / 2
Damage PB/M/L: 1/1/-, Overheat: 0
Class: GL; Point Value: 3
Just a simple, low tech design for a poor, low tech world.
I am the same that I was
And I know fluff can explain everything, I just wanted to know what is the limit.
I plan on making 30 tons with a speed of 3/5, an AC/10 in a turret (with MGs) or a Gauss Rifle without one and 2.5 tons of armour.
Yo' Ice long time no post. The LB 10-X over the AC-10 and Gauss Rifle is the number one for me. In 3095 military CELL engines would be interesting but ICE is fine. Someone turned me on to CELL engines. If your going for a lighter version of the Hetzer I do like armor of 30 on the front that way basic infantry may not kill the vehicle from the front in a turn. At such a slow speed of 4/6 with out a turret. A light hover tank with a simple turret can kill you over easy. With 10 shots, I regret to tell you, I have tested this concept on the board. Your better off with an AC-5 and bump up the speed to a 5/8 or 6/9 so vehicle may turn to shoot at the target. With wheels your stand off is not that good for finding cover. Cover is something your going to want. Check out Mech Mortars 4s over LRMs or AC for ammo improvements and making your vehicle an interesting investment. Do not under estimate primitive tech like two light or heavy rifles and three to four, one shot, smoke loaded, grenade launchers. This is not a tank but support vehicle. I like that you kept it simple. Do not take my input as bad news. At low tech i would go for two Light Rifle with, MG, and two grenade launchers. Or mech mortar and the same combo. A speed of 5/8 so i may keep up with basic tanks like the Vendetta or Stryker. At low tech. I would be packing basic rifle infantry with basic 10 ton APC's. This would be your threats to seek and kill. But fighting mechs a Wasp with rockets or Stinger would be what you test this against. But what will happen if its an old Locust. To fire you would need a crew gunnery of 3 on and move at flank to turn adding +2 to hit plus the movement of the vehicle with a +2 when they walk. a total of 7 to hit at short or 9 at long of 10 but 11 at long. Get lucky. A city fight is where this vehicle would sit with the wheels and then you could do just fine with city fights have no life expectancy.
What my plans are/were is to focus on a family of tanks from Support Vehicles to Combat ones with evolution in tech.
