whatever you do DO NOT put the eagle GT's on your car... here is why
This tire is absolute garbage and we get them back all the time from being total garbage lol
These tires are asymmetrical, meaning they have an inside and an outside, so there is only one way to be mounted, idk what it is about mustangs but they do not like these tires at all. Also there is a reason why these are one of the lowest priced tires in the group.
I always tell people, other than the car itself there are 3 things to never skimp on when it comes to cars
Fluids - oil, flushes, etc
Brakes - pads, rotors, calipers
Just remember you get what you pay for.
and if you go to Big O Tire, tell them an employee from NTB is on your forum with you and told you that he wants the best price you can get him and to treat you well!
as far as the spring, are you saying one broke? or you are wanting to lower the car?
If you do decide to lower it those springs are great, and also look into the Caster Camber Plates. They are needed to help align the car properly. It will keep your tires from wearing improperly