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Old 20th January 2009, 20:12   #46
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Michelin India - Boutique


Michelin india website , it doesnt work on Firefox !

Real nice stuff.
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Old 20th January 2009, 20:22   #47
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Quote:
Originally Posted by Surprise View Post
Are you sure about this?

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



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
It does not work for me. for e.g: 175/65R14 S322s max psi is 44. 10% less makes it 40, still a lot more than what Fiat recommends (28 to 32). Even with 32 and not much load the ride feels like tires are made of stone. It may work for some cars though.
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Old 20th January 2009, 20:31   #48
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Quote:
Originally Posted by Surprise View Post
Are you sure about this?
If the manufacturer recommends 29 psi, 25% is ranging from 22 psi to 36 psi.
Perhaps it was a bad idea for me to state something like that in a public forum.

Let me start by saying that you should ALWAYS go by owner's manual recommendations. I'm not saying that it's OK to get lazy with your tire pressure. As you'll see - uncontrolled tire pressures can lead to unreliable handling.

I tried to find out how my car responded to varying air pressures in the tires. The car is a 1998 Honda Accord.

My front left tire had a slow air leak and it had dropped down to 15 psi several times. There was no clear change in the car's handling despite the 20 psi difference in the tire pressure between the front tires. This sparked me to try several combinations and find out of low tire pressure ever lead to bad handling. Apparently having 1 tires low on pressure simply wasn't a big deal.

I dropped all 4 tires down to 20psi and drove the hell out of the car to see if I could feel anything. The car was the same, but I did note slightly excessive wear especially on the outer edges due to tire flex during hard cornering. I'm sure the tires were wearing faster - but low tire pressure didn't seem to affect the drive much. I did drive the car at it's limit. It felt a bit spongy and vague but that's pretty normal even for this car even with normal pressure lol.

One scanario I didn't test is driving at speeds over 70mph /110kmph in the rain. Driving at those speeds in the rain isn't smart to begin with.

Again - my findings may not apply to all cars, so please do not get lazy with

One setup that I found particularly unstable was having diagonal tires at high pressure: RearLeft 40psi RR 25psi FL 25psi FR 40psi. The car's handling seemed to be compromised and it felt more vague and unpredictable than usual. Under heavy braking + turning, the side with underinflated tires would suddenly tail-happy while the other would "drag" as if I was driving on glue. I think this may have been because of dynamic ride-heigh differences under load.

I'm personally convinced that low tire pressure (IF EVEN) (up to 50%) wont kill anyone but just wear your tires out faster - much faster.

That said - I religiously maintain my tire pressure at recommended levels + 5psi. cheers:

Oh and - an easy way to spot a mistreated tire is to look for a black "halo" on the outside of the tire between the widewall and tread area. This "halo" is created by tire flex due to under-inflation. Once you know what to look for, you'll be surprised at the number of cars with misused tires!
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Old 21st January 2009, 07:32   #49
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Quote:
Originally Posted by Atlblkz06 View Post
I'm personally convinced that low tire pressure (IF EVEN) (up to 50%) wont kill anyone but just wear your tires out faster - much faster.
All your experimentation seems to have focussed on handling and wear.
The central issue of safety has pretty much been skirted.
Low pressure by margins as wide as 25% will lead to extraordinary temperature rise on long drives and eventual burst!
Elevated temperature is one of the worst enemies for a tyre, in any case!
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Old 21st January 2009, 10:47   #50
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from my personal experience i would say that a combination of factors go into maintaing the life of tires and not just proper inflation , timely and professional wheel alignment as well balancing , not to forget Tyre rotation at regular intervals all ,add to the life of the tyre, miss out any one of these and you have a problem on your hands. i generally as a rule have followed the OEs recommendation on tyre pressure and combined with the above mentioned prcautions have been able to real good life out of my tyres. My safari clocked 75 k on the stock tyre. Even with that milage there was a good 5mm of tread left on the tyres.Replaced them as was upgrading to wider tyres and alloys.
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Old 21st January 2009, 11:01   #51
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Quote:
Originally Posted by anupmathur View Post
All your experimentation seems to have focussed on handling and wear.
The central issue of safety has pretty much been skirted.
Low pressure by margins as wide as 25% will lead to extraordinary temperature rise on long drives and eventual burst!
Elevated temperature is one of the worst enemies for a tyre, in any case!
I studied the tire's temperatures immediately after running them with an infrared thermometer and I did not really find elevated temperatures. I dont remember exactly how high they were - but they were nothing to write home about. I do remember that the temperatures were elevated near the edges by a small margin which makes sense. The rear tire temperatures were also lower than the fronts.

I tried to do some searcing and the burst pressure of a tire seems to be well over 100 psi. You will find some nuts running 100psi to perform 2 wheel stunts etc. Of course the tire length will be reduced but it shows that they can handle 100psi for a decent length of time even under abuse.

So I think your idea that a tire will burst from air pressure due to heat is - for lack of a better term - a bust.

Just so you know - I'm not trying to ask anyone to run their tires on low pressure. I'm just interested in experimentation and learning the truth, thats all.
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Old 21st January 2009, 11:43   #52
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Quote:
Originally Posted by cyneverdie View Post
Michelin India - Boutique


Michelin india website , it doesnt work on Firefox !

Real nice stuff.
it surely works on Firefox,you might need to get the latest updates.

My question is that the footpump is 3200Rs,is it the best and most reliable i can get here.
I'm ready to spend some money for this as i'm always concerned about tyre pressure and the thing that irritates me most is that at every bunk the tyre pressure shown is different.

please suggest other options apart from Michelin Footpump.

Thanks
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Old 21st January 2009, 11:50   #53
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Quote:
Originally Posted by watashi75 View Post
If the tyre width increases the contact patch also increases so a lesser pressure is required to support the same load.
I would like to clarify a few points in my statement above. The contact patch does not automatically increase on increasing the tyre width. Infact the contact patch will not change if the load and pressure remains same. Here is a picture (courtesy Car Bible) showing the difference.
Name:  contactpatch1.gif
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In the above figure, the shape of the contact patch has changed but the size remains same.

If now the pressure is decreased, this will increase the contact patch (contact patch = load / pressure). Now, for a given load, increasing the contact patch area reduces the load per unit area, and effectively increases the coefficient of friction (Car Bibles : The Wheel and Tyre Bible Page 2 of 2). What this means for the layman is that if the tyre width is increased but the same pressure is maintained, there is not going to be any gain in grip during acceleration or braking. Lowering the pressure a bit would increase the grip, as well as ride quality.

I hope this information will be useful to people planning to upgrade their tyres for improved performance.

Last edited by watashi75 : 21st January 2009 at 11:53.
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Old 21st January 2009, 14:57   #54
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Anyone used a Digital Tyre Pressure gauge (hand held) lately? Any idea how accurate or reliable they are? Or are the old fashioned analogue ones better?
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Old 21st January 2009, 18:46   #55
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Quote:
Originally Posted by suman View Post
Anyone used a Digital Tyre Pressure gauge (hand held) lately? Any idea how accurate or reliable they are? Or are the old fashioned analogue ones better?
Suman, post # 25 please.

Digital or Analogue does not guarantee accuracy per se; it is the 'sensor' that should be good. Very good quality gauges can be made in each type.
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Old 30th January 2009, 17:20   #56
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Default Right tyre pressure for Innova 225/60 15 Bridgestone

Hi Guys,
Can you suggest right tyre pressure for Bridgestone ER60 turanzas for Innova. Size 225 60 15. It is a V model which comes with factory alloys from Toyota.
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Old 30th January 2009, 19:05   #57
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Quote:
Originally Posted by suman View Post
Anyone used a Digital Tyre Pressure gauge (hand held) lately? Any idea how accurate or reliable they are? Or are the old fashioned analogue ones better?
I just bought a new digital pressure gauge from eBay, used it once - 0.5 PSI accuracy. Will post after using it more often.
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Old 30th January 2009, 19:15   #58
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Originally Posted by ankitahuja View Post
I just bought a new digital pressure gauge from eBay, used it once - 0.5 PSI accuracy. Will post after using it more often.
Hmmmm, you're lucky........
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Old 30th January 2009, 20:15   #59
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MUL recommends 32 for front and 29 for rear in Dzire Zdi. The manual says that the tyres should be over inflated by 5 psi if the vehicle will be driven at high speeds for long duration. Though it does not specify what "high speeds" and "long duration" are. I drove for 500 km recently but didn't follow the guideline of over inflating. Do others do it? How does it help?
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Old 30th January 2009, 20:57   #60
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Over inflation does help in giving better fuel efficiency and faster speeds over long distance. But in terms of comfort it's a small compromise because the ride becomes a bit harsh.
@ mansingh - The tyre brand/make/size etc are not important in determining the tyre pressure. It is the vehicle that is important.
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