I know our tires, Toyo T 1Rs in my case, are rated at 180 MPH or so.

Does the maximum "safe" speed decrease as tire wear increases?

Asked another way: I'm about 50% through my Toyos; am I as safe at 130 MPH or so at 50% treadlife left as I was at 100% (new)?

This may get me the "dumb-butt question of the week" award but I need some words of wisdom from the tech guys on here.

 

My guess is no. Most companies would overengineer the tire for your saftey (and to protect them from cases). Even if it did, Im sure human error would kil you before the tire wear. Also, I think structural integrity is not a function of tire wear, but instead of the tire pressure and the sidewalls and the bead of the tire. Just remember the faster the tire spins, the more it'll stretch because of centripidal forces. Thats probably what limits a tire to a certain speed class.
Thats my edjumacated guessimacation

 

"Thats my edjumacated guessimacation"

Thats funny!

In other words, you know just enough more than I do to be dangerous!

 

ask the tire manufacturer if they have a min tread limit, guessing 3/32"

 

:-D tread is for wet conditions. Less tread = greater grip in the dry.

 

As tread life decrease, you should see a decrease in dry traction, handling, and wet weather traction. Z rated tires are designed with a speed rating of 149+ mph. All this rating means is that the tire's integrity and construction were tested to hold up at that speed. At 50% you should be able to hit your 135 mark in a straight line without any issues but don't expect them to perform as well in the twisties. BTW, 2/32 at any point of the tire is considered legal balding. Most regular car tires come with 10/32s of total thread life.