Team-BHP - Filling the right 'Pound per square inch (PSI)'

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I purchased a new i10 and would like to know what should be the correct tyre pressure? Currently I have 30 in all the tyres.

Tyre information along with recommended tyre pressure will be printed on a sticker on inside of driver door. If memory serves me right, it's more than 30 for 155/80R13 for i10 & i10 also has different tyre pressures for front and rear tyres in full load condition.

Gurus, a question.

I get a hand held guage; and check pressure at home, before moving the car in the morning. It shows 27 PSI. Recommended is 33 PSI. At the filling station, some distance away, it shows 30 PSI.

Now, what should I do?

Fill to 33 psi as recommended? (and ignore the reading I got with the hand held?)

or

Fill to 36 PSI = 30 (the reading at the FS) + 6 being the difference before start?

For simplicity sake, let us assume that all the guages are accurate?

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Originally Posted by BaCkSeAtDrIVeR (Post 1136449)

Fill to 33 psi as recommended? (and ignore the reading I got with the hand held?)

or

Fill to 36 PSI = 30 (the reading at the FS) + 6 being the difference before start?

For simplicity sake, let us assume that all the guages are accurate?

Keep it simple: Just fill to the recommended pressure, COLD condition.
Not much research needs to be done. To be very safe you could exceed the recommended pressure by 2 or 3 psi, but please do not let it be 2 or 3 psi LESS!!

Anup Ji, What if cold filling is not possible. Example: you have driven for about 10 kms when you stop for diesel and check air pressure. Assume that it shows a 2 PSI lower than the recommended PSI. Now how much do I fill up, considering the tyres are hot.

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Originally Posted by BaCkSeAtDrIVeR (Post 1136449)

You can go back home and check the pressure again in your hand held gauge. If you filled 33 and your hand held shows less, one of the readings is wrong and you should stick to the lower one i.e. your hand held. If on the other hand your hand held shows more, you can assume the filling station reading to be reasonably accurate. In this case fill to 34-35 to account for pressure build up due to heat and friction.

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Originally Posted by Eddy (Post 1137170)

Anup Ji, What if cold filling is not possible. Example: you have driven for about 10 kms when you stop for diesel and check air pressure. Assume that it shows a 2 PSI lower than the recommended PSI. Now how much do I fill up, considering the tyres are hot.

This is how I'd do it then: Deflate each tyre. This will also help to cool it down considerably.
Refill to recommended pressure. Or maybe 2 psi higher if you prefer that.

Thanks.

Now another question. How reliable/practical are the PSI recommendations ?

Swift stock tyres (165, 14", JK) are recommended to be filled at 36 and 33 for the front and rear respectively. I find the ride to be a little bumpy and prefer 34 and 32. Am I right or wrong ?

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Originally Posted by Eddy (Post 1137320)

Now another question. How reliable/practical are the PSI recommendations ?

Swift stock tyres (165, 14", JK) are recommended to be filled at 36 and 33 for the front and rear respectively. I find the ride to be a little bumpy and prefer 34 and 32. Am I right or wrong ?

Eddy, the ride will keep getting more & more cushioned as you keep reducing the pressure! So then, are you going to ride around with 17 psi?!! :Shockked:

It is a general rule that 2 to 3 psi higher than recommended will stand you in good stead by way of safety. Certainly not advisable to go for long distance rides at pressures BELOW the recommended value!

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Originally Posted by anupmathur (Post 1137441)

Anup if we keep 2 to 3 psi higher than recommended then with travel the pressure will increase by 1 to 2 psi. Is this safe for the tyre??

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Originally Posted by aka_iitd (Post 1137448)

Anup if we keep 2 to 3 psi higher than recommended then with travel the pressure will increase by 1 to 2 psi. Is this safe for the tyre??

Yes. Safer than starting out on a highway run with 2 or 3 psi LESS than recommended pressure!

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Originally Posted by BaCkSeAtDrIVeR (Post 1136449)

1. All tyre gauges are not correct here and case can not be simplified so much as 5 PSI increase is too much. If you have a gauge with mechanical dial as against digital one it is likely to be correct.
rather then filling station .
Check pressure with you gauge at filling station to see if reading from you gauge and filling station is same.

2. You should also buy a portable Tyre inflator plug it in 12V socket of your car and fill it cold yourself. Adjusting 2/3 PSI with portable pump is not an issue , but don' expect to fill new tyre yourself with this kind of pump. ( foot pump is another alternative if you have no issues using leg muscles)

alternatively find a shop with compressor with in few hundred meters from your home

Indica V2 - OEM 165/65 R13 30F / 28R
Safari DiCOR - OEM 235/70 R16 32F / 35R

I stick to manufacturer's recommendations - city or highway. Tyre pressures are checked religiously every Sunday morning when cold (helps that the bunk is hardly a km away). I also do a check one day prior to long trip - again only cold, and never check during a trip. Visual inspection of all tyres before getting into the vehicle is a habit.

Guys,

Over inflating by 5psi will not kill your tires. Don't over-think this.

Just add 5psi to what the manual recommends and inflate all tires to that temperature when cold or warm and you'll be fine. Stop over-analyzing this down to 1psi - there isn't a measurable difference in safety as long as you're within 25% of recommended levels.

Typically though, under inflation leads to increased gas consumption.

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Originally Posted by Atlblkz06 (Post 1138360)

there isn't a measurable difference in safety as long as you're within 25% of recommended levels.

Are you sure about this?

If the manufacturer recommends 29 psi, 25% is ranging from 22 psi to 36 psi.

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Every tyre has a maximum inflation pressure stamped on the side somewhere. This is the maximum pressure the tyre can safely achieve under load. It is not the pressure you should inflate them to.
Having said this, I've given up using the door pillar sticker as my starting point and instead use the max.pressure-10% theory. According to the wags on many internet forums you can get the best performance by inflating them to 10% less than their recommended maximum pressure (the tyres, not the wags - they already haves inflated egos). It's a vague rule of thumb, and given that every car is different in weight and handling, it's a bit of a sledgehammer approach. But from my experience it does seem to provide a better starting point for adjusting tyre pressures.

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

Though I had pasted the same content earlier in this thread, have missed out lots of points myself. Going through the same has cleared most of my doubts :)