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Old 16th January 2009, 14:20   #1
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Default Filling the right "Pound per square inch (PSI)'

Have come across threads in our "street experiences" where one of the possible reasons for the serious accidents could be not filling/maintaining the right tyre pressure

What are the various factors contributing to determining the "psi" level in tyres? More light on consequences of not filling the right PSI?

PS:Related stuff- HowStuffWorks "How do 30 pounds of air in your tires hold up 2 tons of car?"

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Old 16th January 2009, 14:38   #2
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Good thread. We can post recommended pressures for all cars with stock tyre values and tyre upgrade values as well.
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Old 16th January 2009, 14:48   #3
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I have tubeless Michellins on alloys on my santro xing. At the moment I fill 30 psi on all for wheels pls advice if this is correct or i need to change the it.

Thanks
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Old 16th January 2009, 15:03   #4
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For my wagonR i have taken Goodyear Tubeless, the service agent told me to keep 33psi in all 4 tyres. The ride is bit bumpy some times.
Is this the right psi for my car ?
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Old 16th January 2009, 15:05   #5
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Quote:
Originally Posted by Tejas@perioimpl View Post
stock tyre values and tyre upgrade values as well.
Let me take my case here..

Swift Lxi/Vxi tyre pressure for all four wheels - 33 PSI
Size of stock tyre - 165/80/R14

(read somewhere that Maruti recommends different pressures for front and back, correct me if Iam wrong)

Recommended tyre pressure for stock ZXI - 29 PSI (all four wheels)

Vxi tyre upgraded to Bridgestone of size - 185/70/R14

Do I need to maintain the same PSI of 29 as recommended for Zxi or needed to fill different PSI?

If its same PSI as 29, Can we take that for all tyres of size 185/70/r14, immaterial of the car it runs, we need to fill 29 PSI. If the psi is different from 29, what are the various factors that determines the difference in PSI

Please do share your thoughts on risks of underinflated and overinflated tyres?
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Old 16th January 2009, 15:27   #6
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The tyre pressure is also dependent on the load factor. If I remember correctly, Swift ZXi weighs around 100kg more than LXi/VXi. So the tyre pressure should be slightly less on a upgraded VXi.

Even otherwise, the tyre pressure should be slightly less on a low profile tyre compared to a high profile tyre for the same car. I haven't done the maths so it is open to debate.
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Old 16th January 2009, 15:35   #7
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I have 205/15/55 on my OHC . Tyre guy recommended 30psi front and back.
Recommended for stock was 32 front and 31 back if memory serves me right. Not sure though.
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Old 16th January 2009, 15:39   #8
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Swift VDI (ABS) - Stock tyres

MUL recommends: 36 & 33 for the front and rear respectively.

I fill: 34 & 32
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Old 16th January 2009, 16:15   #9
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Quote:
Originally Posted by Tejas@perioimpl View Post
I have 205/15/55 on my OHC . Tyre guy recommended 30psi front and back.
Recommended for stock was 32 front and 31 back if memory serves me right. Not sure though.
OHC states 29 psi for front and back. That's what the sticker on the door says.

Quote:
Good thread. We can post recommended pressures for all cars with stock tyre values and tyre upgrade values as well.
I would love to see this chart even though this can totally be a personal choice.
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Old 16th January 2009, 16:28   #10
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What is best for Fiesta 1.6 SXI ?

I fill 32psi all tyres. Running on Stock MRF tyres.
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Old 16th January 2009, 17:13   #11
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Swift VDI
195/55/15 - front 32 rear 30
hope its right
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Old 16th January 2009, 17:25   #12
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Does the pressure have to be varied if we upsize the tyres.

MY stock tyres for the lancer were 175/80 R13 @ 30 psi

My new tyres are 185/70R13 @30.
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Old 16th January 2009, 17:52   #13
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I don't think there is one "correct" tyre pressure for all occassions. It depends on a number of factors like total load, desired ride quality, desired handling, weight distribution, desired fuel efficiency, tyre profile etc.

Underinflated tyres run the risk of sidewall heating, overinflation decreases rolling resistance but runs the risk of decreased braking distance due to decrease in the contact patch. Both run risk of uneven wear.

Also, different situations demand changing the tyre pressure - during OTRs you may need to release air to increase traction. You may also need to change tyre pressure to induce understeer or oversteer conditions. Drag setup needs less pressure on the rear tyres.

While upgrading tyres the required tyre pressure will also vary, usually it will decrease. If the tyre width increases the contact patch also increases so a lesser pressure is required to support the same load. A lower profile tyre will need less pressure to maintain the same contact patch as a higher profile tyre.
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Old 16th January 2009, 18:29   #14
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I fill 34 psi in all 4 tyres of my OHC. Seems to work for me. No issues with uneven tyre wear.

Shan2nu
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Old 16th January 2009, 18:43   #15
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Quote:
Originally Posted by watashi75 View Post
While upgrading tyres the required tyre pressure will also vary, usually it will decrease. If the tyre width increases the contact patch also increases so a lesser pressure is required to support the same load. A lower profile tyre will need less pressure to maintain the same contact patch as a higher profile tyre.
Thanks watashi75 for this input.

I agree with you that PSI levels may differ based on specific requirements, but one needs to know the basic correct PSI for filling to do normal day to day driving or highway driving with family.

In my case, even after the tyre upgrade, I did fill the earlier PSI which Iam used to for the past 3 years. One of our members has pointed out in a "Street experiences" thread that higher psi levels as possible reason for the tyre burst on a highway.

In my recent trip via Mysore, I did constant speeds between 100-120 kmph at empty regions with more confidence due to the upgraded tyres of a different make. But I did missed the basics by wrongly filling the pressure , risking the life of all the passengers along with mine

Could not even imagine a tyre burst at speeds in the region of 120 kmph
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