Store only tin[v] for each node. This gives you a DFS preorder traversal numbering.
Use this when you need to check ancestor relationships quickly: is an ancestor of if tin[u] < tin[v] and is on the path from root to . You lose the ability to identify subtree ranges, so this variant is less useful for most problems.
However, combined with tout, you can check ancestry in : is an ancestor of if tin[u] <= tin[v] and tout[v] <= tout[u].