amet

My original post is a good start

also miniature cracks in the tire, I'll snap some photos of my front ones in the morning

Larry Cable

well I tend to err on the side of safety (given that the contact patch is all that
connects my 911 and the occupants to the roadway)...

1) worn to the wear bars or below
2) (uneven) wear patterns across the profile of the contact patch
3) any exposed internals (typically on inside shoulders of the rears on cars that are driven on track or with a lot of camber on them)
4) manufacture date (anything over 3ish years I get rid of)
5) any signs of cracking, blistering or other signs of tire compound or construction damage/failures...

if in doubt, replace, a new set of boots is always going to be cheaper than any other failures&damage (to you or your car) as a result of less than
perfect rubber IMO.

fast1

In addition to the safety factor as incentive for replacing worn tires, there's no less expensive way of replicating the ride of a new car than a four wheel alignment and four new tires.