[Tassem]

Vehicles that are in the yard, storage etc. have tyres inflated to high PSIs to prevent/reduce flatspots in the rubber. This is supposed to be brought down to manufacturer specified levels before delivery. We can also do this if the vehicle is not going to be used or moved often for a long time.

In a similar vein, it's a good idea to keep your spare tyres inflated by 4-5 extra PSI to negate loss by slow leaks etc. so that when you need it, they have adequate air in them. Not many of us check spare tyre pressure as often as check or fill our other tyres.

[clevermax]

Originally Posted by srini1785

Simple fact: Normal atmospheric pressure, that which is all around us is 14.5Psi (1bar). Industrial air pressure settings are of the order of 6-7 bars. A screw compressor can produce upto 12 bar. So, in relation, 40psi (approx 3 bar) is not that high.

Are you talking about gauge pressure? The gauge reads the difference between ambient pressure and tire pressure. A tire with 14.5 PSI absolute pressure would read 0 PSI on a tire gauge at standard temperature and pressure. Going by this, your explanation may be a bit confusing to some.

In other words, when a tire pressure gauge reads 40 psi, it is 14.5 + 40 = 54.5 psi absolute pressure.

[shancz]

Originally Posted by ChiragM

Here are a few cars with high recommended tyre pressures:

Good point.
Also adding WagonR VXi (2016) with recommended pressure of 36psi F/R.

Originally Posted by landcruiser123

I think FE is the main reason.
Also, the budget cars may recommend higher pressure for maximum tire life as they are designed for the cheapest possible OEM tires.

Agree on FE but tyre life hadn't crossed my mind but makes sense.
At 36 F/R, the WagonR feels harsh, 32-34 works well.

[srini1785]

Originally Posted by clevermax

Are you talking about gauge pressure? The gauge reads the difference between ambient pressure and tire pressure. A tire with 14.5 PSI absolute pressure would read 0 PSI on a tire gauge at standard temperature and pressure. Going by this, your explanation may be a bit confusing to some.

In other words, when a tire pressure gauge reads 40 psi, it is 14.5 + 40 = 54.5 psi absolute pressure.

What did i write

Yes. At atmospheric pressure ( 14.5Psi) your gauge would read 0. Then again, no one talks about absolute pressure, only gauge pressure is stated.

[avinash_clt]

Ideally, an OEM will recommend tyre pressures for a model (and powertrain combination) after striking an ideal balance between ride and handling, traction across different surfaces, fuel efficiency, tyre noise etc. Of course the fundamentals of vehicle weight (and distribution), tyre/wheel sizes, max vehicle speed etc will be the starting point.

But more often than not, you tend to find tyre pressure recommendations progressively becoming higher, compared to cars of similar weight and tyre size from 10 years before.
My understanding is that it has got more to do with CO2/fuel efficiency figures that can be claimed during standard test cycles, especially in markets where taxations is directly is linked to it or affecting corporate fleet average values.

To illustrate my point better, look at a older Volvo S60 tyre pressure recommendation chart.


You can see a significantly higher figure recommended by Volvo for 'Eco' use. Also note Volvo specifying higher pressures for high speed driving (Autobahns). I used to religiously follow this on a C30 I had in Netherlands, upping the pressures before driving into Germany.

Notes:
1. It is difficult for a customer to know if the OEM recommended tyre pressure is on the higher side solely for FE reasons. Underinflated tyres are one of the primary causes of tyre bursts.
2. Pass-by-noise regulations are also becoming more stringent and at steady speeds of 60-80 kmph range, tyres are the biggest contributor for noise. I am however not sure if increased tyre pressure positively influences pass by noise measurements.

[Jeroen]

These very high tire pressures on new cars are probably due to the fact that those cars get stored for some time. The best and easiest way to ensure tyres don’t deform during prolonged stand still is to raise the pressure.

I do it every year for the period my classic cars are off the road, during wintertime. I usually go to 150-200% of the normal recommended pressure. It ensures that when I drive the car, after three months of sitting still, the tyres are still nice and round and not square!!

I checked my wife’s tyres on her Ford Fiesta the other day. Her tyre monitoring alarm had gone off.

Not sure about India, but in Europe all cars come with this little recommended tyre pressure plate mounted in the door frame.

Our Fiesta has 195/50 R15 tyres, nothing special. But look at the difference between lightly and heavily loaded.

Front 2,1 resp 2,4 but rear ones are 1,8 and 3,2 bar respectively. I don’t think I have ever come across such huge difference.

Do note that the difference between the lightly loaded and the heavily loaded is not just the number of persons, but also luggage for as many people. How anybody thinks you can cram 5 Dutch persons with the personal luggage into a Fiesta is whole different matter of course!

Even so, don’t get to worried about these difference between the lightly and heavily loaded. I keep all 6 of our cars, tyre pressure wise, on lightly loaded settings. Only when we take a car on a holiday, where we will be taking luggage and more people and would be driving at high speeds for hours will I up the tyre pressure.

What you need to be more concerned about is the accuracy of the manometer as used by your local air-walla!

These sort of manometer simply wear out; To put that in context, here in the Netherlands during the annual MOT on your car, they will also check the tyre pressure. And they need to do so with a calibrated manometer, and the calibration certificate has a validity of only one year. In practice nobody gets their manometers calibrated, as it is cheaper and more convenient to get a new one every year.

A two man MOT station does about 16 cars per day. Using the same air hose, compressor, manometer. Your local air walla probably checks more cars per hour!! So I would say the chances of your tyre pressure being way off due to incorrect manometer reading are far greater than worrying about light/heavy loading pressures!

[rpm]

We took delivery of our Verna recently, and, while fiddling around with the digital instrument cluster, I switched to TPMS, and to my surprise, the tire pressure was a mind boggling 46 PSI for both the front tyres and 45 PSI for both the rear ones . I did have second thoughts about such high pressure because I've gotten used to Spark's 32-34, but I let it be, thinking I didn't know any better. The car has been driving around with that tire pressure for nearly a month now. Only after landing my eyes on this thread and reading the above posts did I realise, that the second thoughts I was having, were quite justified, not to mention the oddly stiff ride, which I thought was uncharacteristic of a Hyundai, and, also, the prevalence of the 'lazy dealership' problem

[Vitruvius]

Talk of car dealers only? I recently got new tires for my car and the tire guy had it installed at 48 psi all tires. I was installing a new tire pressure monitoring system and when I saw the readings I was certain my sensors were erroneous out of the box. I checked it with my tire inflator and eventually bled air to make them 32.

[balenoed_]

Aren't tyre pressure to be recommended by the tyre manufacturer instead of the car manufacturer. I was all this while thinking that was the case.

On a similar note , when I took delivery of the new car, the tyre pressure was at 38, whereas it is 32 that is mentioned in the sticker at the door area. Wondering if I should deflate bit now.

[Cyborg]

Guys, please follow the manufacturer labels (more or less) stuck on the vehicle.

Overinflated tyres during delivery is just laziness on the part of the dealership for not checking this aspect. Tyres are almost always overinflated as they don’t know how long it will be before it finds a buyer. In fact the first thing after delivery during the tank filling, always check/correct the air pressure as recommended.

Cheers

[Rahul Bhalgat]

Originally Posted by balenoed_

Aren't tyre pressure to be recommended by the tyre manufacturer instead of the car manufacturer. I was all this while thinking that was the case.

The tyre manufacturer only specifies the capacity of the tyre to take air pressure.

The actual pressure to be maintained is recommended by the car manufacturer based on the car weight, suspension, desired ride, handling and target fuel efficiency.

Please use the pressure recommended by the car manufacturer. Based on your actual experience, you may tweak it by 2 - 4 psi to suit your needs. But not beyond that.

[Sheel]

Not just cars, Motorcycles too have their share. Most street oriented Motorcycles have around 40 PSI for rear and ~35 for front.

[rpm]

I'm having second thoughts about my TPMS system too. Got them deflated to 35 PSI yesterday, but it still shows 39 PSI. A deviation of 1-2 PSI is understandable, but 4 PSI? Now I don't know if the manometer with the guy who deflated them at the petrol bunk is inaccurate or my own TPMS

[saion666]

The recommended tyre pressure for my car is 32 PSI.I generally check the pressure once a month and have it set to 33 PSI.
By the end of the month it's generally 31/32 PSI when I set it again to 33.

This has worked for me for the last 10 years. All 4 tyres were changed from JK to Yokohama as precautionary changes at the 6 year mark. No punctures.

During lockdown, the car was idle for 6 months and i kept the pressure to 40psi before storing. It was 34 psi after 6 months of lying idle.

[sidharthg]

In my E350, the recommended tyre pressure is 40-42 psi. In the middle years of the car, i.e. I adopted it, but noticed that, the then tyres simple didn't last long. The ride was on a harsher side but FE was better.

However, when I asked the Mercedes SA, even he was perplexed, but since it was recommended on the car it self, he also went along with the same suggestion.

Now I fill up 36 and the tyres seem to last a bit longer and the ride is also pretty ok. So all in all a good compromise. I reckon, the Manufacturers do this to achieve higher FE figures in ARAI testing