In highway vehicle dynamics, which type of resistance is generally considered negligible for a properly designed road vehicle under normal operating conditions?

Introduction / Context:
When estimating tractive effort and power needs for road vehicles, engineers account for several resistances: rolling, aerodynamic (wind), grade (due to slope), acceleration, and minor mechanical losses. Understanding which components materially affect performance helps in quick, safe preliminary design calculations.

Given Data / Assumptions:

• Vehicle is in good mechanical condition with properly lubricated bearings.
• Operation is at normal highway speeds on typical pavements.
• No extreme winds or steep grades are assumed unless stated.

Concept / Approach:
Total tractive resistance is commonly approximated as the sum of rolling resistance, aerodynamic drag, grade resistance, and small mechanical losses. Of these, rolling resistance and aerodynamic drag dominate at moderate and high speeds, and grade resistance dominates on slopes. Bearing or axle resistance is typically very small compared with the others and is often absorbed into rolling resistance or neglected outright in simplified models.

Step-by-Step Solution:
Identify principal resistances: rolling, wind, grade, and minor mechanical (axle).Compare magnitudes: axle losses are orders of magnitude smaller than rolling and wind terms for well-maintained vehicles.For preliminary design, axle resistance is commonly ignored to simplify calculations.

Verification / Alternative check:
Textbook tractive effort formulas usually include rolling resistance coefficient, aerodynamic drag term proportional to v^2, and grade term W * sin(theta), with no explicit axle term, confirming it is negligible or absorbed in rolling resistance.

Why Other Options Are Wrong:

• Rolling resistance: always present from tyre deformation and pavement texture.
• Wind resistance: material at moderate to high speeds; grows with speed squared.
• Grade resistance: significant even on mild slopes due to vehicle weight component.
• None of these: incorrect because axle resistance is the one usually neglected.

Common Pitfalls:

• Double-counting axle losses and rolling resistance.
• Ignoring aerodynamic drag at highway speeds.

Final Answer:
Axle (bearing) resistance