Simple Tire Question

Hello, this is probably a dumb question but I just can’t find the answer so I’m gonna ask anyway. Recently did a few mods to my Mustang GT to add power but now my tires spin out really bad. The thread is still there, just not the kind of tires I need. Was wondering if it would be important to upgrade the front tires as well or if the rear tires make all the difference since it’s a rear wheel drive. Like I said the front tires still have thread and a lot of life left. Thank you for taking the time to help me out with this stupid question!

Conventional wisdom in the tire industry says that the best condition is to have all tires the same size, make, model, and state of wear. That's so the vehicle doesn't behave unpredictably during emergency maneuvers.

Can you violate any of those provisions and still be safe? Yes, but in order to be sure you have to do those emergency maneuvers in controlled conditions and in a suitable location - but that would chew up a set of tires, so if you are going to do this exactly once, it makes no sense to test - but then you are taking a risk, and it could be a big one!

Now what about staggered tire size set ups? Again conventional wisdom is to use the same make, model, and state of wear - with the same proviso if you deviate from that wisdom.

But the extent of the problem is that if you don't test, you will never know until you are confronted with an emergency, and then it is too late.

How bad can this be? I've seen tests where the car was almost undriveable as it approached the limit of adhesion. It would spin out quite violently and quite suddenly. So, Yes! This is a real concern.