Why aren't you supposed to inflate your tires to the maximum that is written on the tires?

Question

I just read an article that says you should inflate your tires based on the guide written on the inside of your car door - not the number written on the tire. Why is that number there if we shouldn't use it as a reference?

My tires, for example, have a maximum PSI 45, but on the door it says not to inflate over 25 PSI. That's a huge difference, especially for someone who doesn't know about the two different numbers. I'm sure this leads to a lot of over-inflated tires, and in this heat the tires could explode.

Answer 1

The 45 PSI is a guide for  technicians as a Max inflation WHEN FITTING. It is the maximum pressure that can be used to seat the tyre into the rim.

For normal day to day driving pressures refer to your manual.

The same size tyre fits a multitude of vehicles all with their own attributes so they will have their own pressures to get the optimum performance from the tyre

Answer 2

Proper inflation is the single most important part of tire care. The inflation pressure on the side of the tire is the MAXIMUM operating pressure.

It is not necessarily the right inflation for your vehicle. Always use the inflation recommended by the vehicle manufacturer.

You can find it in your owner’s manual, posted on the edge of the driver’s door, on a door post, in the center console, or on the inside of the glovebox door.

Always check inflation when tires are COLD: when the vehicle has been driven less than a mile or one hour or more after driving. Use a good quality tire gauge.

Note: It’s natural for radial tires to have a slight bulge in the sidewall at their proper inflation pressure. Check or adjust inflation every few weeks, before any long trip or if traveling with a heavy load. And don’t forget to check the spare.

Answer 3

The only time the placard inside the door is accurate is when you have factory tires.

The maximum on the side is the most you can have.  When you drive the tires heat up and can increase the pressure inside.  The heat of the day can increase tire pressure.  Inflate your tires to 90% of the rated maximum or 40 psi in your case.  Bear in mind that too much pressure can cause the layers of the tire to separate which could lead to a blowout.  Check your pressure at the hottest time of the day (3-5pm) about 40psi would be right for you at that time of day.

25 psi is almost half of your tire's max.  Thats just as bad as overinflation.

Answer 4

45 is the maximum the manufacturer says they can be inflated to. 25 is what the car manufacturer recommends based on the weight and other factors of the car.

Many people inflate their tires up to the tire manufacturer's recommendation to get better mileage, but they're sacrificing a good ride and handling. If they have an accident the insurance company may say over inflation caused more damage.

The tires will not explode if they're filled to 45, even after being run hard on a hot day. This is built into the manufacturers specs.

Answer 5

That number is there as a guide to how much air can be safely put in the tire if need be.Tires can be used on a lot of different cars so you always go by the car manufacturers guide lines.For example you wouldn't want the same tire pressure on a car that weighed 3,000 pounds as you would on a car that weighed 4,000.

Answer 6

It all depends, and the 25psi your referring to is for the tires that the vehicle had from the factory, to produce certain ride/handling/economy characteristics.

I run ALL of my tires at max pressure that is given on the sidewall of the tire.

1. I get better fuel economy from less rolling resistance.

2. I get the maximum carrying capacity of my tire, because it is inflated to the max pressure.

3. My tires run cooler, because of the less rolling resistance.

There is the chance that having too much air (even if it at max pressure listed on the tire) can cause the center of the tire to wear quicker than the outsides. In that case, I would lower the tire pressure till I got good tire wear, but I have never run a tire at what the vehicle says (unless it specs 80psi like on my 1-tons).

I even had load range E tires on my half ton truck, and I ran them at the max 80psi, tires wore great and lasted a long time. I now have a set of D-range tires, guess what they are at 65psi (max listed on the sidewall). The truck door jamb recommends 35 or something like that.

I tire inflated to the max pressure will cause the vehicle to ride slightly rougher, but I think it is more of a mental difference than a physical. If someone put 20psi more in your tires without you knowing about it, most people wouldn't notice a difference in the vehicle. Just because someone knows that they changed the pressure, they are looking for a change...

Your handling characteristics aren't going to be greatly effected. Stopping and turning abilities are practically the same. Your not going to say "I wouldn't have hit that car if I didn't have my tires inflated to the max pressure".