When towing a trailer, which of the following is NOT required?

When towing a trailer, having good tires that are properly inflated is essential for safe driving. Tires that are well-maintained improve traction and handling, which is crucial when towing additional weight. Properly mounted and lubricated wheels also play a vital role in ensuring that the trailer can move smoothly and safely, reducing the risk of mechanical failures while on the road. Moreover, having all accessories including reflectors is necessary for visibility and compliance with safety regulations, especially in low-light conditions.

On the other hand, adjustable weight distribution, while a helpful feature for some towing scenarios, is not a strict requirement for all trailers. Some trailers can be safely towed without needing to adjust their weight distribution, depending on the vehicle and trailer combination used. Therefore, this aspect may not be mandated by law, making it the correct answer for what is NOT required when towing a trailer.