Viktor Drake, on 03 June 2017 - 11:17 AM, said:
I could be wrong but to make up the speed different, the 90 ton mech has to mount a much larger engine, weighing significantly more. The engine weight difference usually will eat up the 5 extra tons meaning you may or may not end up with less usable tonnage at the end of the day. There are a few weight classes where this isn't true for example, the 75 ton weight usually provides the optimal engine weight to free usable tonnage ratio as well as a few other weights.
In the case of 85t vs 90t on a 4/6/3 platform, the 85t unit gets a 340 series engine with 3 x 1t JJ's while the 90t platform gets a 360 series engine with 3 x 2t JJ's. In this case the weight of the engine, internal skeleton and jump Jets add up to more than 5t in difference.