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Old 21st January 2015, 18:25   #76
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Default Re: Correct Tyre Pressures

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Originally Posted by alpha1 View Post
Actually, if we see a tyre is under-inflated, there fore it generates more heat.
Because of heat the air temperature inside the tyre also rises.
Rising air temperature leads to higher pressure.

Thus we should be at the same situation as what we would be if we had filled higher pressure air at the beginning!

How will this lead to over heating or tyre burst?
Hey but the temperature mentioned on your door is tyre pressure in cold condition, they have factored you driving the car and the tyre heating up, air expanding and then reaching the right tyre pressure.

Secondly tyre pressure is load and speed dependent. If your car has just say X tyre pressure mentioned and nothing else, you should vary that according to how you load your car or what kind of driving you would be doing.

For example, I drive mainly on the highways, so my Swift Diesel with 185/70/R14 Michelin XM2 always has 36 Psi in the front and 34 at the rear.

When I am doing city runs, I lower it down to 34 and 32.

Of course, its preference dependent too. Varying a couple of PSI's according to your driving style and conditions would be okay.

But if I were to inflate the tyre to say 28 PSI and load it with 5 people and drive it from Mumbai to Bangalore or Mumbai to Pune, I would call that under inflation.
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Old 21st January 2015, 18:26   #77
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Default Re: Correct Tyre Pressures

Quote:
Originally Posted by alpha1 View Post
Actually, if we see a tyre is under-inflated, there fore it generates more heat.
Because of heat the air temperature inside the tyre also rises.
Rising air temperature leads to higher pressure.

Thus we should be at the same situation as what we would be if we had filled higher pressure air at the beginning!

How will this lead to over heating or tyre burst?
You're overlooking the potential sidewall damage due to flexing stress in the under-inflated tire at high speeds, while the temperature (increased friction due to larger contact patch) and pressure (consequent to temp rise) are simultaneously building up. Weakened tire, running hot and high built-up pressure? Recipe for disaster!

Last edited by Chetan_Rao : 21st January 2015 at 18:27.
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Old 22nd January 2015, 11:42   #78
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Default Re: Correct Tyre Pressures

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Originally Posted by humyum View Post
Hey but the temperature mentioned on your door is tyre pressure in cold condition, they have factored you driving the car and the tyre heating up, air expanding and then reaching the right tyre pressure.
Yes, and my point was that you can anyhow reach that optimum running temperature and pressure. Whether you start with 35 PSI cold or 30 PSI cold.

So why should starting with lesser pressure actually cause a catastrophic condition of tyre burst?


Quote:
Originally Posted by Chetan_Rao View Post
You're overlooking the potential sidewall damage due to flexing stress in the under-inflated tire at high speeds, while the temperature (increased friction due to larger contact patch) and pressure (consequent to temp rise) are simultaneously building up. Weakened tire, running hot and high built-up pressure? Recipe for disaster!
Perhaps you are on to something.
Sidewall damage due to flexing will occur till the point tyre achieves sufficient rigidity. This rigidity is caused solely by the gas pressure.

I start with 35 PSI cold, drive the car and reach an optimum running condition (say on a highway) of 45 PSI. (at 110 deg C)

I start with 30 PSI cold. The tyre flexes more, greater contact patch etc. There is larger hysteresis loss in the rubber (compared to the earlier case) since it is less rigid and therefore raises the temperature. BUT the tyre achieves 45 PSI once it reaches 174deg C.

So therein lies the 'rub'. The rubber deteriorates its mechanical properties alarmingly with higher temperatures.

Thanks for the discussion. I have cleared my doubt.

Last edited by alpha1 : 22nd January 2015 at 11:47.
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Old 22nd January 2015, 12:31   #79
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Default Re: Correct Tyre Pressures

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Originally Posted by alpha1 View Post
Perhaps you are on to something........
Exactly, it can happen both ways.

An under-inflated tire will build up pressure gradually as you drive, but will reach (and cross) optimum operating temperature faster than pressure due to increased friction (larger contact patch), while damaging the sidewall due to increased flex simultaneously. So by the time you've hit optimum pressure, the sidewall can no longer reliably support the prevailing temperature/pressure combination at sustained highway speeds.

An over-inflated cold tire will already be close(r) to its max rated inflation capacity, and by the time you hit optimum operating temps, the tire will be past its safe pressure capacity.

So the point is not just to have correct pressure, but to have the correct pressure at correct operating temperatures at correct loads so the tire is always within its specified operating range for all rated parameters (pressure, temperature and loading capacity).

Last edited by Chetan_Rao : 22nd January 2015 at 12:40. Reason: Grammar
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Old 25th January 2015, 00:48   #80
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Default Re: Correct Tyre Pressures

For the 2014 make Alto k10, the manufaturer recommended cold tyre pressure is 35 psi, both front and rear tyres.

Isn't it too much? My ride is limited to city areas, with one or two occupants usually.

Last edited by wishnipon : 25th January 2015 at 00:48. Reason: added detail
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Old 25th January 2015, 03:04   #81
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Originally Posted by wishnipon View Post
For the 2014 make Alto k10, the manufaturer recommended cold tyre pressure is 35 psi, both front and rear tyres.

Isn't it too much? My ride is limited to city areas, with one or two occupants usually.
It is indeed on the higher end.

Is that pressure given for higher load condition or for all loads?

Do post the picture of the tyre placard.
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Old 29th January 2015, 14:54   #82
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Default Re: Correct Tyre Pressures

I have a Michelin digital pressure guage which I imported a year ago.
The reading is always higher than what the tyre fellows see on their guage. Now, I am not sure which one is more accurate.
Does anyone in Pune have an accurate guage to compare with?
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Old 29th January 2015, 15:12   #83
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Default Re: Correct Tyre Pressures

Recently acquired a Ford Fusion. First thing after I filled fuel was to check the tyre pressure. To my horror, the front two tyres and rear left tyre showed 51 PSI. The rear right tyre had 25 PSI. I immediately requested the attendant to reduce and fill the correct air pressure upto 32 psi. The tyres are MRF ZVTS 195/60/R15.

Last edited by JoseVijay : 29th January 2015 at 15:13.
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Old 7th March 2015, 19:56   #84
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Default Re: Correct Tyre Pressures

Reduced air pressure from 40+ to 33 in all tires immediately after getting delivery of elite i20.
Checked after 1 week, it was again 40+ in rear tires so got it reduced to 33 from tire shop guy. After another week, same thing happened. 40+ in rear tires. Tire shop guy said its normal for tubeless tires. Is it so?
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