A Class 4 MOT covers standard vehicles like cars, taxis, and motorhomes with a gross vehicle weight (GVW) of up to 3,000 kg, making it the most common type of MOT test. A Class 7 MOT, on the other hand, is required for heavier commercial vehicles that weigh between 3,000 kg and 3,500 kg, such as large vans and trucks. Both classes check safety features, emissions, and roadworthiness, but Class 7 includes stricter weight-bearing component inspections due to the heavier loads carried by these vehicles.