Final answer:
Road conditions do not directly affect the maximum allowable gross weight of a commercial motor vehicle, which is determined by specifications and regulations unlike axle spacing, type of cargo, and tire pressure.
Step-by-step explanation:
The maximum allowable gross weight of a commercial motor vehicle is determined by various factors. However, road conditions do not directly affect the legal maximum weight, which is primarily based on vehicle specifications and regulations. The other options: axle spacing, type of cargo, and tire pressure do have a direct impact on the maximum allowable weight. Axle spacing can affect weight distribution and thus the overall gross weight allowed. The type of cargo determines the potential need for special considerations due to hazardous materials or the density of the cargo. Tire pressure influences the safe operating weight limits of the vehicle as it impacts tire load capacity. In comparison, road conditions might influence the safety and practicality of transporting a certain weight, but not the legal weight limits for the vehicle.