The size is usually represented by an alphanumeric slash mark on the tyre's sidewall markings.
The code consists of a three to five symbol indicating that represents tire width, aspect ratio and diameter along with other information such as load index. This helps us know what tire size will fit our car given its model, make, year etc. A common example is P195/65R15 91H where the tyre markings P195 represents the width in mm, 65 represents the tyre's section height in percentage relative to the tyre width (this number is called "aspect ratio"), R stands for radial ply construction, 15 represents wheel rim diameter and 91 represents load rating in kPa.
Below is an example of how to read tyre sizes to get the right tyre for you, complete with tyre specification.Width 195 mm.
Aspect ratio 65 (%).
Tread depth/pattern 15 mm.
Tyre construction (Radial).
Rim Diameter code, PCD & Rim Width 6J x 15 inch (ET 45) or 185mm (PCD 5 X 112mm).
Load Rating/ maximum Speed Rating 91(kPa) Y (240 km h).
Tyre size depends on the diameter of the wheel size and it's important that each wheel has a matching tyre's width and tyre pressure otherwise you could drive on something other than what your vehicle was designed for which could risk the stability of your car/light truck if not safely operated.
The more rubber there is in contact with the road, the greater the car tyre's grip. In an effort to reduce fuel consumption and minimise environmental damage aircraft tyres have been designed with a tread pattern that has as minimal rubber-to-road contact area as possible.
The most common passenger car tyre has a section width of 185 mm and a rim diameter of 15 inches. These aspect ratios differ on if your vehicle has low profile tyres or not.
All-season tyres are designed with a compromise of wet handling, rolling resistance, speed ratings, how much weight and grip in winter conditions. Summer tyres are built to provide the best performance in hot weather, while winter tyres are sometimes designed with more sipes (small slits in the tread) that help with gripping on cold roads if correctly fitted. The latter also have deeper grooves that expel water from the contact patch for increased traction when driving through snow or rain. All-seasons aren't good at any of these things especially if you're living somewhere with harsh winters where they become slick when it's snowing so buying the right tyres for separate seasons will be far cheaper than buying all-seasons.
Quite possibly, yes. You should only ever have four of the same size tyres on your car.
A radial tyre is a tyre in which the cords that run from bead to bead are laid at 90 degrees in the radial direction of travel. Radial tyres have replaced cross-ply tyres on most cars because they provide increased comfort, noise and better fuel efficiency. They also don't require a heavy steel or nylon reinforcing belt under the tread area saying a tire is a radial doesn't tell you whether it's winter, summer or all-season radial.
A worn tyre has no legal minimum tread depth but if your tread pattern becomes less than 1 mm deep then you will need to buy new ones before continuing your journey as it means the edges of your car tyre are beginning to wear away. If your tyre tread is worn down to the legal minimum then you will have far less grip when driving, especially in wet conditions. It's also illegal to continue using tyres that are worn out at 4mm or below because this can make stopping distances longer and increase the risk of skidding.
Yes, car tyres do come with a warranty, but it is usually only limited. During this time there's a good chance that the manufacturer will replace your new tyre free of charge if you have a puncture caused by a manufacturing fault. If you aren't covered, make sure you check what type of tyre warranty your new tyres warranty covers and how long it lasts because many tyre warranties will start to expire soon after buying your tyres.