What does the amount of brake pedal pressure needed to stop a CMV smoothly depend on?

49 CFR 383.111(a)(4) (Basic control); AAMVA CDL Manual Sec. 2.2.3, p.2-8

Pushing the brake pedal down gradually and adjusting pressure based on speed and stopping urgency produces a smooth, controlled stop rather than an abrupt one that could cause cargo shift, jackknifing, or loss of control. This basic control skill underlies safe stopping in every driving situation, not just emergencies.