It depends on the legislation of the country in question
Winter tires should be changed out when the tread has been worn down to around 1.5mm to 1.6mm in thickness, after they have been worn down more they are considered worn out. To measure the tread of ones tires one should use a tire gauge which can be bought at websites such as amazon.
More than narrow tread tires.
In Virginia you must have 2/32 tread depth on all 4 tires to pass inspection.
That's approximately 9 and 1/2 inches across the tread. There are 25.4 mm in an inch
Minimum tread depth for all 4 tires is 2/32"
60% tread wear.
Many tires have tread wear indicator bars molded into the tread. When the tread is worn down to where you can see a solid bar of rubber across the width of the tread, it is time to replace the tire.
According to most states' laws (including North Carolina), tires are legally worn out when they have worn down to 2/32 Place a penny into several tread grooves across the tire. If part of Lincoln's head is always covered by the tread, you have more than 2/32" of tread depth remaining.
I assume you are referring to the tread. High grip will have a more aggressive tread design used in off-road conditions or in deep snow. They are called off-road tires or snow tires. The difference is in the tread design.
While it is good to use tires with the same tread and sizes, it is possible to use tires with different tread patterns, though you should be careful as the performance of the two tires may be different, causing your car to be unbalanced, endangering your passengers.
Because they have more tread.