I am trying to unwrap tire, i would like to have perfectly straight uv map so i can create bump/displacement for sidewall and track. IT looks like mt uv map is very distorted on the edges, what could be done to fix this ? See attached image.
Select the top edge and apply the horizontal constraint. Do the same with the other edges. At this point apply what Chris suggested. If you want to optimize the UV space, consider adding a cut in the middle to get two islands and then pack them.