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Old 7th January 2011, 15:08   #31
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Default Re: Changes in tire pressure - highway driving

Tire pressure is linked to:-
1]Rated capacity by tire manufacturer
2]Load on the tires i.e. unladen + laden
3]Speed at which the car is driven with the said load.
That is why car manufacturers specify a suggested pressure for 2 or 5 persons with and without baggage and also maximum speeds, based on the recommended tire size and ratings.
Whenever the tires are replaced one should recheck with the new tire ratings.

I am surprised so many on this forum are keeping higher pressures. Just one question to all of them Have they ever checked the rated max tire pressure and load inscribed on the tire?
Are we aware that tires are rated according to speed/load ratings! and we Should not exceed them whatsoever! are we also aware that ambient temperature and speed increase tire pressures upto 25%!! in special circumstances.
I know of some Innova taxis keeping 40psi+, and This is Dangerous, as to my knowledge the Innova standard tires are rated to max 40psi.
Just as low pressure can cause a sidewall damage, so also higher pressure can also burst a tire!
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Old 7th January 2011, 15:09   #32
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Default Re: Changes in tire pressure - highway driving

Two things:

1. Bleeding out air before starting on a log drive is a big No-No. When driven at speed tyres do get hot and pressure builds up (up to 10psi in cross plies, 4psi in radials). This reduces flexure and prevents the sidewalls from getting too hot.

2. Dry Nitrogen has no advantage over dry air. The catch is that in many garages the air compressor is in the washing area so the air is moist. Moisture may add up to 10psi to the pressure on running. I always use my own pump and thus avoid this issue.
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Old 7th January 2011, 16:27   #33
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Default Re: Changes in tire pressure - highway driving

The owner's manual for Ford Figo recommends tyre pressure of 36 and 41 for a laden car. I maintain it at 34 and 38 (same for all situations, solo driving and laden).
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Old 7th January 2011, 16:32   #34
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Default Re: Changes in tire pressure - highway driving

This time on my long trip I filled in 32psi in front and 34 psi in rear tyres of ikon, we were 4 people with 3 big pieces of luggage. I found the ride to be comfortable and will probably stick with this combination on long drives.
Other wise it is 31 psi in front and 32 in rear , during the city drives.
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Old 7th January 2011, 16:33   #35
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by scooby05 View Post
I am surprised so many on this forum are keeping higher pressures. Just one question to all of them Have they ever checked the rated max tire pressure and load inscribed on the tire?
Are we aware that tires are rated according to speed/load ratings! and we Should not exceed them whatsoever! are we also aware that ambient temperature and speed increase tire pressures upto 25%!! in special circumstances.
I know of some Innova taxis keeping 40psi+, and This is Dangerous, as to my knowledge the Innova standard tires are rated to max 40psi.
Just as low pressure can cause a sidewall damage, so also higher pressure can also burst a tire!
IMO the rated tire pressure shown is the for cold tires and is compensated for the nominal pressure increase that happens during normal running. As long as you are not doing 120+ km/h continuously for an hour or more, you should be fine even if you inflate at the rated max tire pressure as indicated on the tire sidewall.
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Old 7th January 2011, 18:40   #36
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by sgiitk View Post
I always use my own pump and thus avoid this issue.
Even then, if you live in a humid place you will end up putting moisture into your tires. Solution is to use a dryer system.
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Old 8th January 2011, 08:52   #37
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by dhanushs View Post
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)


You can always 'feel' the heat.

Unless you drive in extreme (F1?)conditions, Nitrogen should behave similar to air.


I believe its with full load. Or else, its a bit high?.
2-4 people in the car. btw, I realised that I did not mention that I don't use manufacturer spec tyres either

I dunno if you've ever noticed, but the specs mentioned are for comfortable city drives, if you drive at any speed with them, you can actually feel the vibrations as the sidewalls flex. Making sure that you have adequate pressure is a must to prevent this.
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Old 8th January 2011, 09:41   #38
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by Neilguy View Post
IMO the rated tire pressure shown is the for cold tires and is compensated for the nominal pressure increase that happens during normal running. As long as you are not doing 120+ km/h continuously for an hour or more, you should be fine even if you inflate at the rated max tire pressure as indicated on the tire sidewall.
That indicated pressure would be considerably higher (~8 PSI) than the pressure recommended by the car mfr. Better to stay at the latter figure or fill 2 PSI more at the max.
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Old 8th January 2011, 10:16   #39
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Default Re: Changes in tire pressure - highway driving

I guess increase of tyre pressure depends greatly on the car you drive.

For me (M800) increased pressure means the car will bob & bounce at the slightest road undulations.

For a car with better suspension i guess it would not make a difference.

I have tried different combinations & found that 29psi front & 27 psi rear is the best for my 800 irrespective of the tyre size (145/70R12,145/80R12, 155/70R12)
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Old 8th January 2011, 12:56   #40
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by Neilguy View Post
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.
Not really my friend ... I am always for keeping same pressure which company has recommended. But in case you have little low pressure then also its fine to hit highways, that's what i am saying.

Generally i never feel air in my car just before going to highways. I never felt any problem. Also i get good FE. With high pressure i feel car bumpy in city driving. With high pressure & driving on highways can cause tire burst as well as fast running will end up increasing pressure by 5-6 PS.

Any expert can throw some light on this issue?
Also let all know if Nitrogen filling in tires really helps? Pressure will remain same after hours of highway driving? Can i mix air partially with nitrogen on highways if required when nitrogen is not available?
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Old 8th January 2011, 21:55   #41
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Default Re: Changes in tire pressure - highway driving

Quote:
Originally Posted by aniketi View Post
Not really my friend ... I am always for keeping same pressure which company has recommended. But in case you have little low pressure then also its fine to hit highways, that's what i am saying.

Generally i never feel air in my car just before going to highways. I never felt any problem. Also i get good FE. With high pressure i feel car bumpy in city driving. With high pressure & driving on highways can cause tire burst as well as fast running will end up increasing pressure by 5-6 PS.

Any expert can throw some light on this issue?
Also let all know if Nitrogen filling in tires really helps? Pressure will remain same after hours of highway driving? Can i mix air partially with nitrogen on highways if required when nitrogen is not available?
It helps, for sure.

1. Nitrogen is comparatively less sensitive to temperature, so tires retain their inflated pressure for longer durations. For a regularly used car, the loss in nitrogen pressure is about 0.5 psi/month, as against regular air that degrades about 3-4 times faster comparatively.

2. Oxygen in regular air oxidises rubber and corrodes metal (which degrades the quality of the tire, the wheel and the valves/seals). Higher temperature & moist air further amplify these effects. Nitrogen, being inert, doesn't have oxidising/corrosive effects.

The performance advantages might not be really apparent (unless one goes racing), but Nitrogen does enhance your tires' day-to-day life by helping you avoid the damaging aspects of regular air.

A disadvantage avoided is an advantage gained, isn't it?

P.S.: When Nitrogen is not available, you can use regular air without worry ( regular air is 78% Nitrogen anyway), but make sure you deflate the tire completely before inflating with Nitrogen again later.

Last edited by Chetan_Rao : 8th January 2011 at 22:00.
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Old 8th January 2011, 22:44   #42
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Default Re: Changes in tire pressure - highway driving

In the i10 I have only seen recommendation based on load. Haven't seen a recommendation based on speed.

I think we should also consider how often the petrol pumps actually get their gauges calibrated. On a recent trip to Hyderabad, I filled up 34 in all 5 tyres (the Hyundai recommended pressure if there is a light load). This was at Shell, Siddhapura. I was there for only 2 days, and decided to check pressure before leaving Hyderabad. This was at Shell, Raj Bhavan Road. To my surprise all 4 tyres showed pressure of 31. One tyre being off could indicate something, but all of them losing 3 PSI was unusual. To double-check I asked the guy to check the pressure in the spare. Voila! It also read 31. So clearly one of the bunks had an incorrectly calibrated machine. I told the guy to fill 32 and left.

Another bad tyre pressure moment was on my trip to Goa from Hyderabad. For those familiar with Hyderabad, this was at the IOC bunk opposite in Madhapur. I asked him to fill 34 which he did. Enroute to Bijapur there was squealing from the tyres when braking. Next morning I got it checked in a local bunk in Bijapur. The reading was 40! I got it to 34 and the squealing while braking was gone. And I am sure this is nothing. Some of the puncture repair guys in small towns over-fill by quite an extent.

Some members have mentioned having gauges at home. But for us rest, I think we anyway must be over-inflating/under-inflating the tyres on a regular basis, depending on the accuracy of the petrol pumps machines!
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Old 9th January 2011, 17:45   #43
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Default Re: Changes in tire pressure - highway driving

Hmmm...this thread is very interesting. I'll speak about some of my own experiences.

I own an Indica Vista Aqua TDi. Tyre size is 175/65 R14 82T Bridgestone B250 Tubeless radials (I'm not entirely sure about the 82T part, need to check) mounted on stock steel wheels. Max pressure is 44psi

The manufacturer recommended Tyre pressure is 30-35psi for front wheels and 28-32psi for rear wheels.

Now, I do a lot of highway driving (50 to 60 % of my driving is on highways). And my car doesn't usually have more than 2 people in it. However I do carry a lot of luggage in the car, which I estimate would add another 100kg to the weight, primarily on the rear wheels.

And therefore I go with tire pressure of 35psi all around (including spare). This is taking the weight on the rear axle, fact that I value FE over comfort, and that my driving is rather rough.

However, the guys at Urs Kar motors in mysore, where I get my car serviced, seem to insist on 28 to 30. Even when I specifically mention the pressure I want on the service sheet, I usually end up making them change the pressure to what I want at the time of delivery. And whenever I ask about it, they say higher pressures cause "suspension damage"

So, I have to ask, are they right? Or should I continue with what I feel comfortable with? I did hear that the old indicas had some problems with their rear suspension and this was changed in the vistas...
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Old 12th January 2011, 18:34   #44
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Default Re: Changes in tire pressure - highway driving

^^I too have this query: Does over-inflating tyres damage suspensions? And, does it lead to faster wearing of the tyres?

That said, I agree with carZest: We can never be sure of the calibration of m/cs at local garages. They might be off by 2-8 psi. I hope the modern m/c s at petrol pumps are more accurate. But, I usually go in for a mid-range of the manufacturer recommended pressure.
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Old 12th January 2011, 20:56   #45
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Default Re: Changes in tire pressure - highway driving

I don't believe 2 PSI more will damage anything, other than causing a sllghtly bumpy ride. It may lead to lesser grip under some conditions, but also enhance FE.

Having some doubts about the calibration at the petrol bunks, I feel it is better to err on the side of a little higher rather than lower tyre pressure.
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