Team-BHP - How To Calibrate Tyre Pressure Gauges?

Hai Tecgurus,

I got pretty confused on my trip to Shirdi 3 days back:

1. I have tyre pressure gauge I picked up from abroad, a little tube with a slider with marking on it, you put one end of the tube into the tyre valve, a slider pops out to show the reading. I have used this all along, last 9 k km or so to keep a constant 32 on all wheels of my Scorp CRDE, on a cold check.

2. I checked the pressure near Triambakeswar, a mallu with a gauge with a broken glass, the round dial with a needle, it said 20 !!!!! That morning I had checked with my gauge, was around 30, filled up at a nearby gas station to pump up 2 points on all 4 tyres. When the mallu filled up to 32 on his gauge, my tube showed 42, an error or 10 points. I didn't want to over fill and get a burst tyre on the run.

3. The mallu said he has been using it for the past 10 years and its accurate. Finally, went for 25 on the mallu's gauge and struck a compromise. The ride was hard, vehicle more bouncy, I felt I had overinflated.

4. To double check near Surat I checked at the petrol pump, guy had the same kind of round gauge with a needle, it said 35 and added to the confusion. Thought the hell with all these guys and filled up to 32 on my gauge, afterall , I have run about 9-10 k kms with it.

The nagging thought; have I underinflated my tyres and damaged them or is my slider correct?

How to bench mark the pressure and where and how to check if my slider gauge is correct?

--Ramky
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Do you keep your guage vertical when using it?

I've always assumed that they work by gravity, and that it should be vertical to read correctly.

I have got one, although not the actual one that I considered more accurate than airpump gauges in UK.

I wonder if these pump guys ever have their gauges checked or calibrated?

I'd be more impressed with someone who said theirs was new, rather than had it for ten years! Always been accurate? Accurate checked against what?

You can get your gauge calibrated at some ISI certified laboratory or workshop.

Another method of checking your gauge at home is as follows: (It looks cubersome and funny but will work).

You will require about 25 mtr of transparent garden hose and a measureing tape of same size. Also a high rise building where you can arrange the garden hose vertically and should be able to check the water level from different balconies. And one person to help you.

Now connect the one end of hose to your pressure gauge and keep it at the bottom of the building. Keep the other end to the highest possible place on the building. Now fill up the hose with water slowly say upto first floor level balcony. Note down the pressure on your gauge and also the water level height (exactly vertical level plumb - do not take the length of kinks and bend of the hose) from the gauge connection point. Repeat it at other floors.

Now you can calcute the pressure with water. Every 1 meter of water from guage connection will create a pressure of 1.4223 PSI or 0.098067 bar. The accuracy of the reading is guaranteed within 0.2% to 0.8%

25 meters of water should give you 35.5 PSI on gauge.
20 meters of water should give you 28.4 PSI on gauge.
10 meters of water should give you 14.2 PSI on guage.

Use any amount of water and just multiply by 1.4223 for every meter of water and voila your guage is calibrated with sufficient accuracy.

Disadvantge/Advantage: Either people with think you are mad or they may think a new Einstein is born :-)

I go to the same petrol pump (Sai Express Way near the Expressway exit - Pune) every time to fill fuel and air.. And almost EVERY time he takes out air instead of putting in more !! i.e. the pump gives a reading of around 34-35. Now where did the extra air come from? Looks like my tyres suck air from the atmosphere or the meter on the pump is faulty (with varying degrees each time it is used) !!

Ramkya1
Do u have a tyre pressure gauge which is something like this??

Quote:

Originally Posted by spadival (Post 667596)

There's an extensive discussion on tyre pressure here

Quote:

Originally Posted by ramkya1 (Post 667783)

Hai Kapan,

I have similar one. Though there may be another thread, I wonder if it discusses the dielamma of calibrating / bench-marking your gauge. See the amount of confusion people have:)

Happy Driving,

--Ramky

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I have the same thing. But I suggest you buy a digital gauge.. I have just ordered one. Need to wait for a few days for it to arrive and then will post the details here.

Quote:

Originally Posted by spadival (Post 667854)

I have the same thing. But I suggest you buy a digital gauge.. I have just ordered one. Need to wait for a few days for it to arrive and then will post the details here.

Hai,

Happy to see I have one more brother with same trouble:D

Is the digital thing available in India, off the shelf / internet? How much does it cost? I think you'd need to change the batteries for this etc., don't know much about this.

Happy Driving,

--Ramky

I had a digital gauge in London. It was fiddly to read, unreliable, and eventually broke completely. It was also expensive*.

I returned it to the shop in the last month of its one year warranty and got my money back, but wasted the price of a test change of batteries.

Whether it is a dial-type, or the rod type, I think simple mechanics will be more reliable than electronics for this kind of task.

I suspect that there is a tendency for us to equate 'digital' with 'accurate'.

That is not the case!

But, spadival, hope your new toy turns out to be good. Let us know --- and also cost and source?

*I don't remember how much. I'd guess at equivalent to Rs800 to Rs1200.

Quote:

Originally Posted by spadival (Post 667596)

The tyre pressures should be set at the recommended levels when the tyres are cold, say in the morning before the car ha done any running. Near the Expressway toll gates (either entry or exit) the tyres would be hot because you would have done good speeds for several kms and the tyre pressures would be high. That is not the right time to check the pressures.

@Ramkya1: The pencil-type gauge that you are using is known to be inaccurate and unreliable. E.g. see the section titled "Lies, damn lies and tyre pressure gauges" in this website:

Car Bibles : The Wheel and Tyre Bible Page 2 of 2

Quote:

Originally Posted by ramkya1 (Post 667783)

I have similar one. Though there may be another thread, I wonder if it discusses the dielamma of calibrating / bench-marking your gauge. See the amount of confusion people have:)
Happy Driving,
--Ramky

No sir. I didn't suggest u that thread. It was for Spadival who was having doubts regarding tyre pressure.
My dad got that gauge some 10 years back and i never liked it. Never felt it was giving the right reading.

Quote:

Originally Posted by ramkya1 (Post 667868)

Is the digital thing available in India, off the shelf / internet? How much does it cost? I think you'd need to change the batteries for this etc., don't know much about this.

I'm also on the look out for a good accurate gauge.

Hai PPL,

I went thro the thread which discussed the issues of tyre pressures/how much on which car/ hot & cold, more / less etc, it also discussed on the gauges a little.

It would be worth-while to focus on how to calibrate against a referance and how to bench-mark the guages.

Other than the explanation of 25 mtr tube, filling water and testing segment by segment (though sounding crazy, difficult to do & is is scientific) there doesn't seem to be any scientific / accurate way of bench marking, so far, or have we missed something?

RKS: I agree with you on my pencil type gauge being not accurate, I tested it when the tyre nozile was on top, I slider slid out quickly and showed a pressure of 50 psi (aided by gravity) ;)

Happy Driving,

--Ramky

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Quote:

Originally Posted by kpzen (Post 667951)

No sir. I didn't suggest u that thread. It was for Spadival who was having doubts regarding tyre pressure.

I'm also on the look out for a good accurate gauge.

Yeah.. I forgot to mention in that post that I was looking out for a more accurate benchmark for tyre pressure. Hopefully, the digital one will be better than that pop out one, again.. no guarantees. But its better than relying on the pump meter alone.