What do YOU consider the cutoff? I hear all kinds of differences from other people WRT considering a tire for dry only riding WORN but I dont want to show up to the track and immediately be told I need new tires, I prefer to plan ahead. Right now Im on Q4s that are just starting to scuff the wear bars right where you put the power on (maybe a MM from being flush to the bar). Intermediate (and bottom 3rd of that group) if that makes any difference.
From the Tech Requirements Tires and brakes must be in good condition. Tires should be at least 50%+ of new condition. Any tires that are bluing from excessive wear will be disallowed. We will have on-site tire service at most events, so if your tires don't pass, you may have the opportunity to put on replacement tires to pass tech. Based on your description of your tires they don’t meet this requirement.
Just following up. Ran at barber and nobody had an issue with the tire @ tech. Was able to run the rear until noon before it started slipping on me and then just had the onsite crew swap it for one I brought.
I've not seen someone fail tech from tire wear, unless they're worn completely out they will let you ride from what I've seen.