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Old 24th February 2015, 14:05   #61
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Default Re: Tire pressure - Strange question with No answer - can you answer?

If not anything else this proves how careless people are about tyres. If a mechanical engineer believes that he need not check air pressure, unless the tyre has a puncture, then you can imagine the awareness of the lesser educated folks.

Basically he is relying on the visual deformation of the tyre to say that it is punctured and needs attention. As long as the tyre appears inflated, he is happy to assume that air pressure is maintained.

Most times when you have a puncture, you see the flat tyre and immediately know that the tyre is punctured and you need to get it fixed. But sometimes with tubeless tyres, a nail can puncture the tyre, and also act as a plug which does not allow air to escape quickly. In this case it may take a week or a month for the tyre to completely lose air. Its the risk of running on an under inflated tyre that you'd want to eliminate by regularly checking air pressures.

I check air pressures about twice a month with my own gauge and find that some tyres are excellent in retaining pressures and can go even six to eight months without needing a refill, while some tyres lose about 1 or 2 psi a month. Anything more this is a puncture or a valve leak. Visually its hard to tell a 24 psi inflated tyre from a 30 psi inflated one. Which is why its important to periodically check air pressures. Underinflated tyres are the no. 1 cause of tyre blowouts on the highway.
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Old 24th February 2015, 14:09   #62
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Default Re: Tire pressure - Strange question with No answer - can you answer?

Air in the tyres does escape in tiny quantities over a period of time. Nitrogen also does, but at an even slower rate. So the pressure will certainly reduce - I have observed this myself. So it's best to check the pressure and top-up the tyres at regular intervals for safety purposes.

As for your cousin's Eeco, I think the service centre guys must be checking the tyre pressure while doing the wheel rotation/alignment/balancing during routine services. Another point is that the Eeco uses LT or Light Truck radials (as far as I'm aware of), and the recommended tyre pressure is generally in a higher range for LT radials compared to normal passenger car radials. Since the pressure is higher, even a little loss over a period of time makes the tyres appear to be normal on visual inspection, but running at a lower pressure than recommended nevertheless. Do advise your cousin on the need to periodically check the tyre pressure.

Last edited by RSR : 24th February 2015 at 14:33.
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Old 30th June 2015, 11:59   #63
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Exclamation Different petrol bunks = Different tire pressure reading ! ?

Hello all,

I have been owning a Santro for the past 5 years having done ~65,000 Km's till date. Company fitted tires were Apollo Accelere with which I did ~47,000 km's. Refitted with the same company and type tires as i was pretty satisifed with its all season performance

All these years have been observing one common phenomenon - The tire pressure filled at different petrol bunks.
Let's say that I filled petrol on an IOC petrol bunk and filled air to 30 psi (which is the company recommended) and drive around and in the same day I face a situation of filling petrol in another bunk and when I check air there. In this situation what do you expect the tire to be ?
30 psi right ? well the reality is its either less or more but almost never, "never" 30 psi

Been thinking about a lot of factors which might have come into play here

1. Temperature of the air filled inside the compressor of the air pump (as air expands on heat and becomes lighter)
2. Improper maintenance of gauges at petrol pumps
3. Expansion of air inside the tire due to the rise in tire temperature caused by friction from all that driving around hence leading to increased pressure
4. Time at which the air compressor at the petrol pump was switched on in the first place

Now, would like to get all your inputs on what all might be the influencing factors and how to tackle them to attain the advised air pressure at all times
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Old 30th June 2015, 12:18   #64
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

Quote:
Originally Posted by Tamarind View Post
Hello all,

The tire pressure filled at different petrol bunks.
..... lot of factors which might have come into play here

1. Temperature of the air filled inside the compressor
2. Improper maintenance of gauges
3. Expansion of air inside the tire due to the rise in tire temperature
...

how to tackle them to attain the advised air pressure at all times
  • The tyres need to be well rested before filling, driving for a short 2 to 3 km to the pump for filling should be ok.
  • Its very dangerous to fill in air in the middle of a journey when the tyres are hot. I always ensure to fill at least a day or two before the journey.
  • Its better to get a small guage to check the pressure once in a while (if you are ever in doubt after filling at an unfamiliar place) I have bought this model (Coido) Some of these inexpensive guages will have an error of +/- 1 or 2 PSI. Its ok as long as you know how much error your guage has and you'll be able to add the correction to the reading.
  • As far as possible, its better to get the tyres filled at the same place everytime.
  • I recently purchased a tyre inflator (ResQTech), but i'm not making use of the same. Its more of a hassle, have to keep the engine running (waste of fuel) and takes quite a lot of time. Its just lying in the boot as a backup. Topping up at pumps is a lot easier but have a pressure guage handy to cross-check if required.

Last edited by for_cars1 : 30th June 2015 at 12:33.
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Old 30th June 2015, 12:24   #65
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

Yes, this is a very common phenomenon. Earlier it frustrated me when there was a change in tire pressure, with changing air filling stations. Finally, I cam up with a simple solution. Now, I fill up my tires at 35 PSI at the station, and then set it to my required limit (29PSI) as per my air gauge. Yes, i have bought one after witnessing these differences. The problem I think is the use of different air-gauges at stations.
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Old 30th June 2015, 20:15   #66
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

Yes, I have observed this in many petrol pumps in Kolkata too. Actually these air dispensers are supposed to be calibrated from time to time, which it seems is not done and even then it is done haphazardly. Finally, I too get my tyres slightly overfilled and adjust with my own guage at home later when the tyres are cool.

Last edited by techiecal : 30th June 2015 at 20:16.
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Old 30th June 2015, 20:59   #67
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

I too have noticed this issue. Normally, we get our car refuelled at a HP or a Shell petrol bunk, since these are the two nearest to my house and I've always noticed that the Shell bunk shows a higher air pressure than the HP one. Once, my dad got the air filled at a road side puncture repair shop. Although that guys gauge showed a pressure of 32PSI, at the HP petrol bunk, it showed 36PSI.
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Old 1st July 2015, 11:57   #68
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

Quote:
Originally Posted by Tamarind View Post
Hello all,

Let's say that I filled petrol on an IOC petrol bunk and filled air to 30 psi (which is the company recommended) and drive around and in the same day I face a situation of filling petrol in another bunk and when I check air there. In this situation what do you expect the tire to be ?
30 psi right ? well the reality is its either less or more but almost never, "never" 30 psi
There are only two causes for reading mismatch:
1. Genuine. Caused by different temperature of air inside your tire. First time when you fill the temperature may be 40 deg C (some driving). Second time it may be 60 deg C (longer driving). Third time it may be 30 deg C (at rest). Since you tire volume is constant, pressure is directly proportional to the temperature.

2. Spurious. Caused by calibration errors. All instruments need to be calibrated against a master standard regularly. But then the people operating such device need to be educated and intelligent enough to know this important fact of life.
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Old 1st July 2015, 12:27   #69
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

Nobody bothers calibrating these gauges. Forget petrol pumps, I don't think even tyre outlets and wheel balancing centres who are in the tyre business bother too much about this aspect.

I've seen tyre gauges at petrol pumps that are off by nearly 5 to 6 psi. Best solution is to get a decent analogue gauge and keep it in the car, fill up a little extra at the pump and set the correct pressure with the help of your own gauge by releasing pressure in small amounts.

Tyre pressures make a huge difference to how the car rides and handles apart from the obvious safety issue. I am sure a lot of lives can be saved in addition to precious fuel savings, if Govt. makes a proper TPMS mandatory in all cars instead of those useless headlamp levelling devices.
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Old 1st July 2015, 14:25   #70
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

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Originally Posted by Santoshbhat View Post
Nobody bothers calibrating these gauges. Forget petrol pumps, I don't think even tyre outlets and wheel balancing centres who are in the tyre business bother too much about this aspect.

If Govt. makes a proper TPMS mandatory in all cars instead of those useless headlamp levelling devices.
There is a rule saying that all commercial measuring devices like petrol pump dispensers ,auto rickshaw meters , weighing machines at grocery stores or markets must be calibrated by professionals ,duly stamped (sealed to prevent any tampering) and verified by inspectors or assistant controllers from department of legal metrology . But those people are as corrupt as anyone else . No one bothers to check these guages .
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Old 10th August 2015, 15:07   #71
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

Quote:
Originally Posted by for_cars1 View Post
  • I have bought this model (Coido) Some of these inexpensive guages will have an error of +/- 1 or 2 PSI. Its ok as long as you know how much error your guage has and you'll be able to add the correction to the reading.
Quote:
Originally Posted by keeprevving View Post
Now, I fill up my tires at 35 PSI at the station, and then set it to my required limit (29PSI) as per my air gauge. Yes, i have bought one after witnessing these differences. The problem I think is the use of different air-gauges at stations.

The description of the item says it can show pressure in PSI as well. But after purchase i was able to see that the device has only lb/inch and kg/cm^2

So you need to manually convert it all the time !
Is this the same in your case ?
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Old 10th August 2015, 16:10   #72
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

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Originally Posted by Tamarind View Post
[/list]

The description of the item says it can show pressure in PSI as well. But after purchase i was able to see that the device has only lb/inch and kg/cm^2

So you need to manually convert it all the time !
Is this the same in your case ?
Yes, I do it manually. Most of the times the reading always tend to be higher than my preferred limit.
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Old 10th August 2015, 16:16   #73
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

Quote:
Originally Posted by Tamarind View Post
[/list]The description of the item says it can show pressure in PSI as well. But after purchase i was able to see that the device has only lb/inch and kg/cm^2

So you need to manually convert it all the time !
Is this the same in your case ?
Correct me if I am wrong. Isn't lb/inch = PSI [ Pounds Per Square Inch ]
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Old 10th August 2015, 19:13   #74
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Default Re: Different petrol bunks = Different tire pressure reading ! ?

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Originally Posted by lambuhere1 View Post
Correct me if I am wrong. Isn't lb/inch = PSI [ Pounds Per Square Inch ]
You are right !

I checked it here, and was surprised to see that there are two units to denote the same measurement criteria ! !

My bad :P was measuring the pressure in bar and then was converting it to PSI using the value equivalent chart printed at the back
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