[Red Herring]

Don't ride around Lydden (or any track for that matter) with a squared off rear tyre. More than one person has come to grief doing so (including at least one fatal that I witnessed). As the tyre rolls across the pointed bit of the profile as it does coming out of Chessons it has a nasty habit of letting go, and given you are at the top end of third gear at this point it isn't nice. Profile is far more important than tread depth.