car tires strength vs car weight?

Tires hit bumps at speed. They have to hold up to the shock of impact.

The side wall of the tire is the most vunerable to sustain damage.Heat and high temperature causes cracks.Blow outs can occur. Rubber ages with temperature and time.The tires have to be designed to over come the tear and wear.

Do tyres get weaker with age and wear?

Do cars ever hit potholes or bumps increasing their effective weight?

The rating is the MAXIMUM PERMISSABLE load not the best or most reasonable load.

So I will give you an example. On a pushbike a tyre of 32 mm can carry a mass of 120 kg.

I have a mass of 70 kg and only 2/3 of that is on the rear tyre. ie about 50 kg is supported by the rear tyre.

My wife is 55 kg and on the same tyres hers suffered from a lot fewer stone chips and lasted at least a year longer.

I replaced my rear tyre with 35mm. Now my tyres don't suffer from stone chips and they last as long as hers.

So even though the tyre would not burst with 120 kg on it, the tyre would have a very short service lifetime.

( one heavier person reported 2 thousand km on his tandem and my tandem gets 20 thousand km from its tyre a HUGE difference in the economic cost of using the bike. So "overtyring" reduces the ownership cost and the failure rate ).

There are several reasons:

1. People do not always drive around in an empty car and some times they overload it.

2. Hitting an object at speed multiplies the effective weight of the car. This concept of pounds per second needs to kept in mind.

3. Remember the pounds per second concept- a tire has to be able to provide traction. This is called adhesion and tires need adhesion for acceleration, braking and of course steering. As a car is stopped it must have enough adhesion to stop the car and when the adhesion of the tire is not enough the tire can not stop the car effectively- it breaks loose. The same is true in cornering. So a car will have weight reserve hopefully enough to provide the adhesion needed for safety.

Other answer is correct. Tires are not made specifically for each model and brand of car, one tire covers many models.

and, having extra strength is a plus, not a minus, as hitting a pothole can put much more stress on the tire.

Would you like a dining room table that just barely can hold the weight of your dinner? So that if you put one elbow on the table it collapses? I don't know how much weight my table can hold but I'm confident that, even with loaded with dishes and food, it's well below the limit.

With a car, every time you go over a bump, the suspension compresses and a lot more weight is put on the tires for a brief period. Have you ever accidentally driven over a curb? If you're going up a steep hill, much of the car's total weight is on the back wheels. You want to be well below the maximum weight to allow for this, to allow a safety factor so your tires won't just pop like balloons every time you go over a pothole.

Has it not occurred to you that other cars may weigh and carry more weight than your car? Tires are mass production items that cost less when produced in volume.