Large Goods Vehicle (LGV) Theory Practice Test

Tread depth is about maintaining grip and shedding water, especially in wet conditions. The requirement focuses on the central portion of the tyre width—the area most in contact with the road—specifically the central three-quarters of the breadth. The smallest depth that still counts as legal in that central band is 1 mm, meaning if the tread there drops to 1 mm or more, it meets the minimum standard. The other figures are higher than the minimum and would indicate more tread than the minimum necessary; since the question asks for the minimum depth, 1 mm is the correct choice.