Truck Startable Grade (Traction Limit)

The drive tires push only with the friction on the weight over them: max startable grade (%) = 100 (mu (W_drive/W_gross) - f), with mu the tire-road friction (~0.6 dry, 0.3 wet, 0.15 ice) and f the rolling-resistance coefficient (~0.012 on pavement); available tractive effort = mu x W_drive. An 80,000 lb combination with 34,000 lb on the drives (42.5% drive fraction) can start on about 24% dry but only 5% on ice -- why loaded rigs get stuck on icy grades that look mild. More weight on the drives and better traction raise it. A STARTING (traction) limit, not a sustained-climb (power) limit. Small-angle field form; wheel slip and weight transfer shift the real number. First-principles statics (SAE J2188 gradeability). A planning estimate; the driver, the surface, and the truck govern.

max startable grade (%) = 100 (mu x (W_drive/W_gross) - f); available tractive effort = mu x W_drive. mu = tire-road friction, f = rolling-resistance coefficient (small-angle field form of mu W_drive >= W_gross (sin theta + f cos theta)).

Traction-limited gradeability, first-principles Newtonian statics; SAE J2188 defines gradeability, but the physics is public and self-contained.

The traction/grade-resistance balance is first-principles statics; the weights and friction/rolling coefficients are the user's inputs.

Estimate. AHJ and licensed professional govern.

Field names used by the API: gross_weight_lb, drive_axle_weight_lb, friction_coeff, rolling_resistance_coeff, max_grade_pct, tractive_effort_lb

• Traction limit max grade (%) = 100 (mu (W_drive/W_gross) - f); tractive effort = mu W_driveNewtonian statics / SAE J2188
• Small-angle field form grade ~ sin theta; wheel slip and weight transfer shift the real number; a starting limit, not a sustained-climb limitscope of this tile