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-   -   The right tyre pressure? (https://www.team-bhp.com/forum/tyre-alloy-wheel-section/3273-right-tyre-pressure-11.html)

To begin with one should set tyre pressure when the tyres are cold. On a summer day tyres pick up heat real fast and readings would change, with couple of kilometers of driving. So find the nearest filling station to your home or office and use that to fill the tyres, ideally early in the morning or late evening when the temperature is relative less.

Alternative is for you to get a small digital air pressure gauge and portable compressor so that you can correct the same at your own parking, when the tyre is cold. Don't rely on the gauges that comes with compressor coz that will need some trial and error to figure out what the right reading is. Yes but they generally are within 2-3 psi range.

Manufacturer recommended air pressure would be favoring FE more than ride comfort, so if you ride around alone you can try 2 psi less from the recommended pressure.

Regarding the variation between stations, well it is a reality and only way to avoid that is to carry your own air pressure gauge and fill using the station. A digital gauge will cost you about 800-1000 bucks but a worthy investment.

PSI is a unit to measure air pressure = Pounds per square inch
1 psi = pressure when 1 pound of force acts on a surface of 1 square inch.
The more the pressure is in a tyre, the more quantity of air (molecules of air) is inside the tyre.

Now coming over to the issue that you faced:
1. You can't help it. Any measurement of any physical entity has to be done via ACCURATE and CALIBRATED instruments.
You would be surprised to know the (lack of) accuracy of most of the air pressure instruments. You would also be astonished to know that they are never calibrated.

2. In spite of the depressing scene highlighted above, aim to measure the tyre pressure when it is cold. The pressure reading increases with temperature too, so you wouldn't want your tyre to be filled with less number of molecules simply because the pressure reading was showing high.

3. Perhaps accuracy doesn't really matter that much. What I do is pretty simple: move out of the vehicle and kneel down. Check the tyre sidewall profile from the front/rear of the car. The side walls should not bulge out.

Pounds per square inch

https://en.wikipedia.org/wiki/Pounds_per_square_inch

My car is Toyota Vitz. It has stock tyres which is 165/70R14 81S. The recommend tyre pressure according to door sticker is Front: 250 Rear: 240. As our local tyre shops inflate tyre at PSI gauge so I collected user manual of this car and found that the recommendation in PSI is Front: 36 Rear: 35. But when I went to the local tyre shop to inflate the tyres and asked to inflate as per car recommendation the attendant said higher PSI in front tyres will make the car jump. So he inflated Front: 32 Rear: 35.

Same goes to the spare tyre. Its size is T125/70D16 95M and recommended is 60 PSI but the attendant put 40 PSI.

So should I hear that local tyre shop or do as recommendation?

*a supplementary question: My main tyres size is R14 but spare tyre is D16. This spare tyre was not included with the car, it was kind of a gift from the seller. On the manual I saw that the spare tyre size for this car is D15. So should I change the spare immediately?

Another thing, The nearest tyre shop is about 6 km away from my home. I have read as the tyre gets hot after running 1/2 km I should increase PSI in addition to my recommended PSI. But how much should I adjust?

PS: I didn't see an edit option so I quoted my own reply stupid:

Whenever you go for topping-up air, fill in around 1-2 psi more than what is recommended. If you are filling when the tyres are cold the fill in what is recommended by the manufacturer.

In your doubt, driving for 6 km the tyre will not get 'hot' so you can fill in 1-2 psi more.

Bringing this thread back to life. :D

I drive a Hyundai Verna. The nearest dependable (and more accurate than others) air filling station is around 10 km from my place. When I start from home, the tyre *looks* under inflated but when I reach the air filling station, the machine shows around 55-60 PSI. The 10 km drive includes speeds of 80-100 kmph with moderate, fast-moving, traffic (means I can not manage to drive at a steady 40 kmph).

The attendant at the pump fools everyone by reducing the air pressure of 9 out of 10 cars! Mostly people are unaware whether the pressures mentioned on driver door panel are cold tyre pressures. Since the tyre gets hot (as they were driving like seconds before checking), the machine displays 50+ PSI or sometimes even 72 PSI (in a VW Vento) and the attendant diligently brings the value back to 30 or 32 PSI. The tyre will be under-inflated as the pressure will decrease when the tyre will cool down. I have tried explaining this to the attendant but he doesn't budge.

Now what can be done? I am ready to purchase a digital tyre pressure gauge (if that costs under 1k). I can manage without a compressor as I have a manual foot pump with me and quite a strong body! lol: Experts please chip in and let me know the best possible option -

1. Get a digital gauge and check the pressure yourself at home, on cold tyres. Do let me know the options as I am looking forward to using such a device.
2. Get nitrogen filled as they use proper machine to ascertain tyre pressures and have knowledge of the hot-cold thingy.
3. Wait outside the air filling station till the tyres cool down and then get them filled. Though it depends on how much time it will take to cool down.
4. Adjust some PSI above or below to compensate for the heat after driving. Again how much to adjust, a big question!

PS. Once a friend's Activa was punctured and he had to wait for an hour (as the attendant had gone to get a tube) at the pump. We had checked the pressure of the non-punctured tyre and the machine showed 31 PSI. Thus the possibility of the machine being inaccurate is also ruled out. Also nitrogen filling is a bit unfavourable for me as I travel to remote places often and need the most-common form of air available at times. (In) My other cars (tyres) are filled with nitrogen.

I think you should invest in a good quality pressure gauge and an air-pump. I too came upon this thread looking for a reliable & sturdy air pressure gauge, so guys, please suggest :)

Now, I usually get it checked at a place which has an alignment and balancing center. It shows accurate readings. My car, rather SUV has tire pressure & temperature information as well, so I do rely on them too.

In biggrin's case, will taking out all the air from tire, waiting for ~5 mins and refilling help?

No tire shop/alignment center nearby? If a tire shop is near by and trucks don't ply on that route, reading should be accurate.

If the vehicle has run for 2 kms plus during warm summer days 2 PSI more is quite safe. If it has done very high speeds and more than 10-15kms continuously, better avoid filling or wait for atleast 10-15 mts before pumping air.

Fill fuel and try getting a get a cup of coffee or tea, that would help, before filling air :)

I already have a manual foot pump (as well as the longer one, which is used for bicycles) and it will work for me even though the quality is far from satisfactory. At home, when the tyres are cold, I can fill the tyres sufficiently (say 40-45 PSI, with all my might!) and lower accurately using a good pressure gauge.

I had ordered the air pumps online for 250 and 110 bucks (foot pump and normal respectively). The former even has a pressure gauge but isn't accurate at all.

There are many small puncture-walas near my home but all of them use the standard, flimsy looking, chrome plated gauge with a shivering, shuddering and small needle. :D Plus most of them go upto 150 PSI or so with markings of 0-10-20-30-40... PSI, hence values like 31 or 32 or 33 PSI can not be correctly calculated. The air filling station I take my car to is a fairly busy one in a fuel bunk with 2 new machines (with compressor) showing digital values.

What has lack of trucks got to do with readings being accurate!? stupid:

I had a TPMS in my Swift where the normal tyre that is inflated at say F=33psi & R=31psi (cold tyre pressure), after a 56 kms drive with mixed speeds used to go upto 46 psi in hot condition post the drive. So the readings reaching 70 psi is difficult unless one is trying to drive like a F1 racer which too is impossible so I doubt that gauge.

What I suggest you is, get a good pressure gauge (Michelin) and a tyre inflator. The pressure gauge would be around 1500 and inflator would be around 1000. Keep the inflator in the car for emergency.

I changed from normal air to Nitrogen for my bike. The guy at the filling station told me to keep 2psi less than recommended one. He told me for nitrogen it is better to keep 2psi less than normal air.

Is it so? Should be there this difference between nitrogen & air filling?

Then, most probably, the machine is not correctly calibrated. I thought that it was the best thing available in my area. I definitely saw 72 PSI in a VW when I was there for top-up for my Verna (and on that day, one of the tyre was at 59 PSI). Thanks for the finer details.

Actually I read on the internet that the increase in pressure is more in under-inflated tyres than in properly/over inflated ones. Since your tyres were properly inflated before the drive, the increase in pressure was under 15 PSI. And it would have been more if the tyres were at 26-27 PSI before the drive.

That Michelin gauge is pretty expensive. :p If there is no significant difference in durability and/or accuracy, I would give the MGA gauge a try. At 500 bucks, I think it is well worth it since any basic digital gauge will cost around 300 bucks from the market. Plus I have around 300 bucks in my Maruti card (don't remember what it is called!), so the effective price would be very reasonable.

Any idea on how these gauges work (digital ones) and what can go wrong in the long run? I plan to use it around 2 times a month (on only 1 car). There is one 'Coido' brand available online for the same price as MGA. Which one would be better of the two (MGA or Coido)?

Also approx. how much difference can I expect in the reading in these digital gauges (difference from actual PSI figures)?

I recently changed the tyres 205/55 R16 in my Merc C class with Michelin with the same specs. Earlier with the OEM goodyear tyres the tyre pressure recommended was 29/32 psi front/back. Do i need to change the tyre pressure in these new tyres since the construction and material may be different?

Secondly, i also changed the tyres of my Santa Fe from the OEM Kumho to Michelin latitude sport 3, with the same dimensions and spec sof the OEM tyres ie: 235/60 R18 103 H. Same question? The recommended tyre pressure for light loads was 33 psi and 42 psi when fully loaded, i believe.

The cars do ride better, handle better and the noise levels have reduced substantially.

Hi !

Have just changed Manza's tyres from the OE 185/60/ R15 Bridgestones to Michelin Primacy 3 ST 195/60/ R15.

I need inputs on the recommended tyre pressure. The manufacturer recommended pressure is 32 PSI and I follow it . I only increase 3-5 PSI over the recommended pressure when the car is fully loaded and has to head to highways.

Will I have alter it after the upsizing? The change in dimensions is given in a comparison below. On the left are the dimensions for the stock tyres while on the right are the ones for upsized.

Cheers !