Same tires, different cars = different recommended tire pressure
Different tires, same car = same recommended tire pressure
This doesn’t make sense to me. Why is this?
In: Engineering
Ummmm…. car manuals give you the tire pressure for the tires.
They base off cars due to weight etc
Truly, any non-OEM tire may require a different pressure. It is generally safe to stick with what is on the car’s door jamb, but different compounds, sidewall types, load ratings can effect the “best” tire pressure. Luckily, passenger cars are forgiving here so 30-35 psi (sorry, freedom units) is just fine for 90% of these vehicles. If you did change wheel size and tire aspect ratio, you’d want to experiment by feel and possibly a “chalk test”. You may even want different alignment settings.
Different cars weigh different amounts. That makes them require a different PSI in the tires to maintain a proper amount of traction.
Have you ever sat on an exercise ball and noticed how much it squished down? Then think about a kid sitting on the same ball, and how it’ll squish less? The ball is the same PSI in both scenarios, but it is holding more weight when you sit on it. This means that it gets squished into the ground more.
The same is true with tires — more weight = more squish. You want a certain amount of squish so that you have a certain amount of the tire in contact with the ground. You could have two cars that use the same tires, but one weighs 2000lbs and one weighs 2500lbs. If you use the PSI for the 2500lb car on the 2000lb car, your tires might not have enough contact area to maintain a good grip, and you’ll lose traction while driving.
Recommended tire pressure on a car is based off the car manufacturers recommended tire pressure for optimal driving in terms of handling, efficiency, and safety.
That depends on many factors of the car itself, its weight, wheelbase, length, height, etc.
The tires are able to work under many different pressures without breaking, so manufactures optimize pressure to the car not the tire.
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To try to simplify this discussion away from the technical aspects of tires, suspensions, and cars; instead of thinking of the tires as balloons to be inflated to a particular size, think of them instead as mattresses to be adjusted to the different people lying on them.
The optimal tire pressure depends on two things
1. Contact area of the tire – this is determined by the tire’s dimensions, width mainly
2. Weight of the vehicle
The tire pressure times the contact area will equal the weight of the car. If you under inflate the tires then the sides sag and more makes contact with the road, and if you over inflate the tires then it gets pointier and less makes contact with the road.
The tire only knows the first information, the car maker knows both because they specified the width of the tires that your car should be using. There could be tire pressure changes between cars of the same model but different trim levels if the 4WD ultra premium version adds another couple hundred pounds to the weight it could add 1 psi to the recommended tire pressure.
The specified tire pressure tries to keep the tires at their ideal shape for even wear, good grip (but not too much), snappy handling (but not too snappy), and acceptable noise. The tire could come with a charge of PSI by vehicle weight but its far more reliable to just always put it on the car
Imagine chopping your tire in half, the grippy bit should be as flat on the road as possible not enough air and it will go flatter, also a heavier car will make it go flatter.
Put too much air in and it will start to go round on the bottom, lifting the edges a bit.
Optimal tire pressure is not a static setting! The total weight of the car includes all passengers and cargo. The difference between 1 driver vs +3 or 4 passengers and 7 days of luggage can mean 1000 lb difference! You’re supposed to increase and decrease tire pressure as the weight of the loaded car changes
My car has different pressures for front and rear. The front of the car weights more and the rear needs the lower pressure to help with traction.
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