What Does Compatibility Mean in the French Code de la Route?\n\nIn French driving theory, compatibility is not just a general recommendation—it is a strict legal requirement. It encompasses both technical compatibility (how vehicle parts work together safely) and administrative compatibility (how your driving license matches your vehicle configuration). Operating an incompatible vehicle or trailer setup poses severe safety risks, compromises vehicle handling, and can result in your insurance being voided in the event of an accident.\n\n## Mechanical and Tire Compatibility Rules\n\nOne of the most critical applications of compatibility on the French theory exam relates to tires. Under French law, tires fitted on the same axle must be highly compatible. Specifically, they must share the exact same:\n- Brand and tread pattern (recommended for optimal handling)\n- Structural type (radial or bias)\n- Dimensions (width, aspect ratio, and wheel diameter)\n- Load capacity and speed rating index\n\nMixing radial and cross-ply tires or having mismatched tire sizes on the same axle is strictly forbidden and results in an automatic failure during the French technical inspection (Contrôle Technique).\n\n## Trailer Towing: Weight and License Compatibility\n\nAnother major exam topic is compatibility between your vehicle, a trailer, and your driving license category. This is calculated using the Gross Vehicle Weight Rating (known in France as PTAC - Poids Total Autorisé en Charge):\n- Category B License: Allows you to drive a vehicle-trailer combination if the trailer's PTAC is 750 kg or less, or if the combined PTAC of the towing vehicle and the trailer does not exceed 3,500 kg.\n- B96 Training: Required if the combined PTAC of the vehicle and trailer is between 3,501 kg and 4,250 kg.\n- Category BE License: Required if the trailer's PTAC exceeds 750 kg and the combined PTAC of the vehicle and trailer is between 4,251 kg and 7,000 kg.\n\nAlways verify the vehicle's registration certificate (Carte Grise) to confirm the Gross Train Weight Rating (PTRA) is not exceeded.\n\n## How Compatibility is Tested on the ETG Exam\n\nTheory test questions frequently present scenarios involving trailer weights or tire replacements to test your decision-making. You will be expected to calculate whether a specific driver holds the compatible license category for a given vehicle-trailer combination, or identify whether a vehicle with mixed tire types is legally allowed on the road. Memorizing the key weight thresholds and axle requirements is essential for scoring well on these technical questions.