|Stuff you don't fight with a 10 ton mech.|
A hidden penalty is hiding in the construction rules of The Battletech Compendium. It's the units of 1 ton or 1/2 ton per part added. Some of the math results in values much lower than a half-ton, but rounding dictates either full ton or half-ton depending on the reading.
Personally, I modify that rule to be 1/4 ton because .75 and .25 are just as easy to add as 1 and 1/2. It's not a "grab" to do this, it is just convenient to pair .75 tons of gyro to a 1/2 ton machine gun and 1/4 of ammo. It's not battle-effective, but it makes a lot of mechanical sense from a manufacturing point of view.
One way to analyze mechs is to build them backward. A 10-ton mech needs a 3-ton cockpit, 1 ton of Internal Structure, an engine, and a gyro. The engine and gyro weights are linked. On the table below, everything in parentheses uses my 1/4 ton rule.
|Mech Tonnage||Cockpit||Internal Structure||Engine Rating||Gryo Size Rating/100||Engine Tonnage||Remaining Tonnage|
|10||3||1||70||1 (0.75)||2||3.0 (3.25)|
|10||3||1||60||1 (0.75)||1.5||3.5 (3.75)|
|10||3||1||50||1 (0.50)||1.5||3.5 (4.0)|
|10||3||1||40||1 (0.50)||1||4.0 (4.5)|
|10||3||1||30||1 (0.50)||1||4.0 (4.5)|
|10||3||1||20||1 (0.25)||0.5||4.5 (5.25)|
|10||3||1||10||1 (0.25)||0.5||4.5 (5.25)|
As you can see, the 1/4 ton rule modification doesn't do much at all except for the extreme last two cases. It does make a difference in larger mechs.