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Old 3rd January 2011, 13:29   #16
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Default Re: Changes in tire pressure - highway driving

IMO, there is no need to increase the pressure irrespective of the load and the speeds. If it were the case, the car manual or something like that should mention that clearly. Isn't it?
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Old 6th January 2011, 18:26   #17
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Default Re: Changes in tire pressure - highway driving

What exactly is the rationale behind over-inflating tires?

AFAIK, Tires have their specific load factors, and recommended pressure is provided by the manufacturer. Some even provide unladen/loaded pressure standards.

As long as I adhere to the above standards, no. of passengers/terrain should be irrelevant, surely?
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Old 6th January 2011, 20:19   #18
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by Shan2nu View Post
No it should be 3-4psi more. Reducing pressure will increase the load on the sidewalls, causing them to fail.

Shan2nu
Correct!! Danger of tire bursts.
Also lesser tire pressure means higher fuel consumption .

Maruti says 30 psi for 145/70r13.I always keep 34 psi on highways in the 165/60r13 G3's
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Old 6th January 2011, 21:10   #19
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by flyingkolors View Post
IMO, there is no need to increase the pressure irrespective of the load and the speeds. If it were the case, the car manual or something like that should mention that clearly. Isn't it?
The tire pressure sticker on my Xylo clearly indicates the increased PSI required with a full load. IIRC, it's 41 for fully loaded (7 pax) and 35 for regular single/double driving.
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Old 6th January 2011, 22:38   #20
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Default Re: Changes in tire pressure - highway driving

What a beautiful thread !

For me, I usually add 2 psi's extrs for a highway trip. What I have read is that increasing tyre pressure will reduce the heating of tyres while doing highway runs and will improve the FE as well.

Also increasing the tyre pressure will add bumpiness to the drive - But then mostly i will be in drivers seat alone and i really dont bother about the bumpy ride.

For me, its safe to add couple of more psi's as even if the extra air get discharged, we are still in the green zone of pressure.

Does it make sense?
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Old 6th January 2011, 22:54   #21
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Default Re: Changes in tire pressure - highway driving

Well my point of view is

The tire pressure given by the manufacturers is an ideal one where in the driver is below 70kgs and the total average weight of the passengers is around the same mark, But it is hypothetical so there is an note for adding +2 psi for full load.

Higher pressure is both a bane and boon as the overall performance increases the safety decreases. With high pressure filed in tires the car tends to ride over pot holes etc with ease increasing the speed and mileage and compromising on grip offered. So its each to his own.

Tire pressure's are best checked when the car is left over night and the air in tires gets cooled down. If you dont have such an apparatus at home the tire pressure remains unchanged till 2kms before the tires get heated up.
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Old 6th January 2011, 23:06   #22
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Default Re: Changes in tire pressure - highway driving

Here is a bridgestone article -

Tyre pressure tips
Contrary to popular belief, tyre pressure is not determined by the type of tyre or its size but
upon your vehicle's load and driving application i.e. speed

To find out what your car's tyre pressure should be, consult the manufacturers tyre placard usually found inside the driver's door sill, glove box, fuel filler cap or under the bonnet.
The placard also displays the manufacturers recommended tyre sizes.
Tyre pressures should be checked when the tyre is 'cold', as pressure increases as the tyre becomes 'hot'.
Take the "cold" reading and check them against the recommended tyre pressures from your placard.
Heavy loads or towing puts an extra strain on your tyres. So if your vehicle is fully loaded with passengers and luggage, the general rule is to add 28kpa (4PSI or 4lbs).
At high speed, (defined as driving at 120km/h for over one hour), your tyres will wear out twice as fast as when you drive at 70-80 km/h. If your tyres are under-inflated by twenty per cent tyre life can be reduced by thirty per cent. The rule here is to add 28Kpa (4PSI) from your Minimum Compliance Plate Pressure. Don't inflate your tyres above 40 psi or 280 kPa. When the tyres get hot from driving, the pressure will increase even more.
Believe it or not, checking your tyre pressure can have a big impact on our environment. An under-inflated tyre creates more rolling resistance and therefore more fuel consumption. By keeping your tyres inflated to their proper levels, you can help maximise your car's fuel economy and minimise its impact on our environment.

Tyre pressure tips

apprently heat produced in tires is due to the collission of the molecules in the air. if inflated low, more space for molecules to move, hence friction (between molecules) and increase in tire temprature.

over inflating by 2-4 psi will result in more tightly packed molecules and lower tire temperature.

the above is my understanding of the same
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Old 7th January 2011, 07:43   #23
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Question Re: Changes in tire pressure - highway driving

When is a tyre in cold condition? When the tyre stops revolving for more than X minutes?

Now if I am driving from my house to fill air which is lets say 2-3 kms away, does the tyre still remain in cold condition when I reach the filling station.

If one were to fill Nitrogen instead of air, would it also be subjected to same expansions as air. Also if the load were to be increased, would some top up Nitrogen as per the manufacturers recommendations.
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Old 7th January 2011, 12:58   #24
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Default Re: Changes in tire pressure - highway driving

Interesting topic. But one basic question from my side ...

When company is recommending you the ideal tyre pressure for your car then why play with it? We should maintain same in my opinion. Company must be thinking of luggage & 5 passengers while designing the car & choosing the tyres. Am i wrong? Experts please correct me if i am wrong ...

I have observed that when i ride about 2 hours on highways tyre pressure goes up by 5-7 PS in radial tyres. So having right or slightly low pressure on highways is better IMO.
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Old 7th January 2011, 14:21   #25
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Default Re: Changes in tire pressure - highway driving

All I can say is that I go 6-8 psi (front) and 4-6 psi (rear) over manufacturer recommended specs whenever I hit the highways
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Old 7th January 2011, 14:28   #26
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by flyingkolors View Post
IMO, there is no need to increase the pressure irrespective of the load and the speeds. If it were the case, the car manual or something like that should mention that clearly. Isn't it?
The recommended pressure is mentioned usually on a label on the door sill. That label will tell you the recommended pressure based on the load in the vehicle in a combination of no. of passengers and load in the boot. Following that in a strict sense is impractical as you will have to carry a compressor with you at all times. You should work on an average load condition - if you carry 4 passengers most of the time or it is the wife and you in the drivers seat mostly. Choose accordingly.

As far as speed is concerned I have not seen any recommendation by manufacturers about modifying the pressure depending on the speed of the vehicle. However, under inflation will lead to more tire wear at higher speeds. The Merc workshop recommends that I stay within 4psi of the recommended pressure. I inflate all wheels to 34 Psi. Anything more makes the ride hard and uncomfortable. I measure the pressure frequently (I have a Moroso gauge) to ensure the pressure stays at 34psi.

As you drive, for every 1 degree increase in tire temp there is generally a 2 psi increase in pressure. I found this out as my earlier car I had a TPM fitted which reported in real time the temp & pressure of each wheel. The change in temp will depend on the weather and also on the weight of the vehicle (friction with the road surface) In summer a 14 km drive under usual traffic conditions for a Honda Accord in Calcutta can raise your tire temp by 3 to 4 deg. resulting in a pressure increase by 6-8 Psi. This is not insignificant.

I do not understand why I need to increase the pressure on long drives - IMHO I will rather bleed out a couple of Psi to make the grip better at higher speeds.

I will suggest stay with the average conditions. The manufacturers know their products better than we do.

Rgds
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Old 7th January 2011, 14:30   #27
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Default Re: Changes in tire pressure - highway driving

Maruti recommends to increase the tyre pressure by 5 PSI over the normal 30 PSI while travelling on highways. (SX4 manual)

Murthy
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Old 7th January 2011, 14:37   #28
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by gavinimurthy View Post
Maruti recommends to increase the tyre pressure by 5 PSI over the normal 30 PSI while travelling on highways. (SX4 manual)
5psi! Maruti-Suzuki must know something that tyre manufacturers do not!
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Old 7th January 2011, 14:39   #29
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by aniketi View Post
When company is recommending you the ideal tyre pressure for your car then why play with it? We should maintain same in my opinion. Company must be thinking of luggage & 5 passengers while designing the car & choosing the tyres. Am i wrong? Experts please correct me if i am wrong ...

I have observed that when i ride about 2 hours on highways tyre pressure goes up by 5-7 PS in radial tyres. So having right or slightly low pressure on highways is better IMO.
You seem to be contradicting yourself. In one sentence you say we should adhere to manufacturer's recommendations and in the next you say that having lower pressure is better.

IMO the manufacturer's tyre pressure recommendations for Cold Tire pressure must be calculated taking into account the slight increase in pressure for high speed or highway runs since it applies to the general population (read: not enthusiasts).

But again, I fill around 2-3 psi more than the recommended pressure for unladen vehicles, but definitely not crossing the max PSI mentioned for laden vehicle. This is to compensate for any errors in the tyre pressure guages that we have at our regular roadside (or petrol pump) air filling stations.

Last edited by Neilguy : 7th January 2011 at 14:42.
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Old 7th January 2011, 14:39   #30
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by flyingkolors View Post
IMO, there is no need to increase the pressure irrespective of the load and the speeds. If it were the case, the car manual or something like that should mention that clearly. Isn't it?
Every car will have a tyre placard, that mentions the same clearly. Like this - http://www.team-bhp.com/forum/techni...ml#post2177000 (Skoda Yeti - Tyre Pressure Advice)

Quote:
Originally Posted by ghodlur View Post
When is a tyre in cold condition? When the tyre stops revolving for more than X minutes?
You can always 'feel' the heat.
Quote:
Originally Posted by ghodlur View Post
If one were to fill Nitrogen instead of air, would it also be subjected to same expansions as air. Also if the load were to be increased, would some top up Nitrogen as per the manufacturers recommendations.
Unless you drive in extreme (F1?)conditions, Nitrogen should behave similar to air.
Quote:
Originally Posted by teknophobia View Post
All I can say is that I go 6-8 psi (front) and 4-6 psi (rear) over manufacturer recommended specs whenever I hit the highways
I believe its with full load. Or else, its a bit high?.
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