Gents a couple of items I scrounged for a primer to Core-Rifts.
"If if ain't broke, don't fix it.
My nature is to tinker and so I have to always remind myself not mess with my computers, ideas, and friends that don't have a problem. When I first came up with the idea of fixing Palladium's Rifts by using the Dream Pod 9's Silhouette rules, the above thought never crossed my mind. RIFTS was broke an needed to be fixed. But on retrospect, the thought that RIFT's isn't broke may cross other people's minds so let me illustrate for you why the I'm trying to fix it.
The origin of the RIFTS system comes from the Palladium Fantasy RPG and provided an effective level based system for that genre. It was a simple offshoot of D&D d20 based system with a few ingenious twists for handling armor effectiveness and personal damage. As the Palladium company added game lines with modern or sci-fi settings, instead of developing a new system for those settings, the author chose to bolt on rules to cover the modern weapons and armor. This was a mistake in system design as the add on rules convoluted the simplicity of the mechanic and did not truly address how modern weapons/armor interact. Beyond that, a new damage class was added for powerful vehicles. This damage class came with too great a conversion factor and, as a hit point based system, again did not address how modern machines handle structural damage.
As a simple example to the above argument let me present a shooting an Intercontinental Ballistic Missile (ICBM) at the trademark armor unit of the RIFTS game, a Glitterboy. Based off capabilities, the large missile (nuclear) approximates a short to medium range ICBM. If it were to successfully strike a Glitterboy, it would, on average, reduce the Glitterboy to one third of its vehicular hit points and the Glitterboy would move on with little further effect. This is a ludicrous outcome.
The feeling of suspense that combat should evoke is a feeling not readily seen in the RIFTS mechanic. That lack of feeling is ultimately the reason RIFTS is broke and needs fixing.
On the opposite side, Dream Pod 9's Silhouette system was designed from the beginning to handle mecha and vehicular combat as evidenced by the first games to come out of that publishing house, Project A-ko (1994), Heavy Gear (1995), and Jovian Chronicles (199?). Every one of this games featured robots and vehicles of all shapes and sizes and handled them in a simple, effects based, realistic system.
But don't take my word for the Silhouette system, analyze it. To resolve an attack, the attacker and defender make a contested roll with generally 2d6 each. From that roll a comparison is made to determine the accuracy and effectiveness of an attack. This is the simple element. If attack was accurate enough to hit and cause less than catastrophic damage, a roll is made on a damage table to determine how the target's capabilities will be degraded or "effect". Catastrophic damage will remove the vehicle from play immediately with no further rolls. Overall, a realistic simulation for damage in modern vehicular combat.
Conveniently, Silhouette also features a design system to build almost any vehicle you might think of, including all the vehicles, robots, and power armors of RIFTS. Using the base statistics (weight, speed, crew) and written description of a Glitterboy, deriving a Silhouette version is pretty easy. One thing that quickly becomes apparent, based of the armor limit by size of a vehicle, the Glitterboy is no longer nigh invulnerable.
Considering the previous illustration of an ICBM successfully hitting a Glitterboy in the Silhouette system, nothing would be left on the power armor. This is a more much more satisfying result.
As a matter of fact, all weapons become more deadly when placed in the Silhouette rules, which makes for better RPG stories. Stories where getting into combat brings tension and forces thinking, knowing that poor tactics can mean the death of any player.
Hopefully this explains why the conversion rules exist and, further, that you enjoy using them to make great stories."