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Old 7th April 2007, 12:08   #1
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Default Over inflation of tyres

I keep reading posts about over inflation of tyres here on team-bhp but no clarity with regards to it being a good or a bad thing,so I looked up the bridgestone india site and they seem equally confused ,somewhere they write over inflate your tyres by 5 Psi for high speed driving and elsewhere they write stick to your manufacturer recommended inflation pressure.

Now we keep hearing about overinflation of tyres being good for Fuel efficiency but some feel it is just a myth and you would achieve those figures even with the recommended tyre pressure figures.

Debunking a Mileage Myth: Can You Really "Pump Up" Your Fuel Economy?

Now with regards to safety issues,an australian government agency says over inflating is as dangerous as under inflating your tyres.

Quote:
Overinflating car tyres can be as bad as under inflation, the Motor Vehicle Repair Industry Authority warns. Underinflated tyres cause excessive wear, cause the car to use more fuel and make steering and braking unstable. They are a common unseen factor in many accidents, the MVRIA says. "We regularly remind owners to have the tyres correctly inflated. I am now receiving reports which suggest some owners are being a bit too enthusiastic and are overinflating tyres," spokesperson Colin Brown says. "Overinflation reduces the amount of tyre in contact with the road so it is quite dangerous. And it also causes excessive wear in the centre of the tyre."

Modern cars have manufacturer's recommended pressures on an information plate and owners should follow that, the MVRIA says. The lower pressure is good for low speed around town driving and it should be increased for highway driving but only to the maximum pressure indicated on the tyre information plate.
Source:
MVRIA - Media:Storybook-Wheels & Tyres (Part 2)

It would be really nice if somebody where to throw more light on this topic as to whether over inflating your tyres is recommended or not?

Last edited by rahul_intlad : 7th April 2007 at 12:10.
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Old 7th April 2007, 12:37   #2
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IMO excessive over inflation is definitely bad. The required PSI suggested by both vehicle manufacturers and tire manufacturers is different for different loads and driving conditions. So the definition of overinflation is w.r.t driving conditions.

I have come to know of two affects of overinflation

1. Uneven tire wear: more center wear if overinflated.
2. Affect on the suspension/ chassis components, I was warned the lower arms could be damaged by over inflation.
3. Ofcourse ride quality, I find it a little harshes even for a 1 PSI increase in my car.
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Old 7th April 2007, 12:45   #3
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Yup what sreenivass says is correct.

If you overinflate the tyres the tyre takes on a round shape. As a result the centre has more contact than the side of the tread. This leads to uneven wear. More over the contact patch reduces and the handling is affected.

The overinflated tyres do not absorb shock since they cannot flex as much. As a result the ride becomes harder and all the shock is transferred to the suspension causing premature suspension wear. This can also lead to sidewall of the tyre getting damaged when you hit a bump at high speeds.

Also when the tyre heats up on the road we all know that the air expands so the air inside expands and automatically will result in higher pressure inside when the tyre is hot. So there is no need to actually overinflate as this will cause further overinflation when the tyres heat up.

That is also the reason it is recommended to fill air in the morning with cold tyres.

The only thing good overinflation does is slightly better mileage due to lesser contact patch and rolling resistance. The acceleration will be a little better as well.

It is definitely not recommended to overinflate by 3-4psi. At a max you can play with +/-2psi from recommended pressures.

Last edited by Vid6639 : 7th April 2007 at 12:48.
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Old 7th April 2007, 13:04   #4
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Nice topic. And a very controversial one, with probably as many opinions/practices as there are drivers. The carbibles website of Chris Longhurst is strongly biased in favour of overinflation. One point I would like to note is that even those who advise to stick to manufacturer's recommendation cite only grip and uneven tread wear as the reasons -- not that they fear a tyre burst due to overinflation. As for fuel economy, I read a website (which I am not able to locate) that during a fuel economy run for some company (Subaru?), some of the participants overinflated the tyres to 60 psi!!!. Again Chris Longhurst makes tall claims w. r. to fuel econony (up to 25% increase due to overinflation in his Subaru). Probably will vary from car to car and from driver to driver.

I personally have not found any uneven tread wear in my S322 tubeless tyres even after 12500 kms, despite keeping tyre pressures at 35 psi. And the grip is very good, at least in dry conditions. Probably advisable to go back to manufacturer's recommendation of 30 psi or maybe at most 32 psi for monsoon season. Ultimately, it is one's own experience that matters most -- there canot be a general rule due to the large number of factors involved (car, road, driving style,...).

Edit: @sreenivass and vid6639, do you have any references for the possibility of suspension damage due to overinflation. I specifically searched for this possibility, but could not find any. The roads in India are very bad and those who recommend overinflation probably do not take this into account, since they are mostly foreigners. But I did read that *underinflation* is bad for the suspension. And I do not agree with vid6639 that sidewall damage is more likely with overinflation. It is with underinflation, as sidewall flexes more. But possibility of tyre damage due to impact on stone/kerb increases with overinflation. You have to drive more carefully on bad roads.

Last edited by rks : 7th April 2007 at 13:15.
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Old 7th April 2007, 13:40   #5
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Underinflation will cause damage to the tyre as well as to the wheel if you go over a pothole.

whereas overinflation will damage the sidewall if you go over a pothole/stone or even a speedbreaker at higher than normal speeds. If you overinflate the tyre you are basically leaving no room for flex since youve stretched it to the max. any impact thereafter will result in the sidewall taking the shock and since it cannot flex anymore it may get damaged.

Basically you are already putting mechanical stress on it by overinflating. hitting a pothole will have more stress on the sidewall possibly beyond it's limits.

Take a ballon for example you blow it up beyond a certain point and you are on the limit and even something so small as a poke of a finger may burst it.

For the suspension part I dont have any references it's only from experience that I'm saying that. Think about it the ride becomes hard. What that means is that the tyres are not absorbing the small bumps and are transferring it to the suspension.

Last edited by Vid6639 : 7th April 2007 at 13:42.
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Old 7th April 2007, 14:21   #6
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Here is the link to an interesting web discussion (not a particularly knowledgable one, though):

Tire overinflation | Ask MetaFilter
The question:

Quote:
The sticker in my Malibu Maxx prescribes tire pressure of 30 psi; the sidewalls on the tires list a maximum pressure of 44 psi -- is it OK to run them at 35 psi, or higher, to gain better gas mileage, or will the money saved be nullified by shortened tire life?

Further info: I'm currently getting about 28 mpg at 35 psi, with about 80% highway miles, 20% city. I was getting lower mileage at the prescribed 30 psi, but that was also during much colder weather.
Quoting some opinions:

Quote:
(1) Go with the figure on the car itself for performance as the car was designed. A little overinflation as you seek should not hurt performance and may actually improve your cornering a bit. It will probably also save you a few cents per fill-up. On the downside, the tires are less resistant to road damage from potholes and stuff when overinflated.

(2) Do what the car manual says. The sidewall is informing you of maximum safe inflation pressure; the tire company is mandated to put this information on there. .... Don't inflate your tire to the listed sidewall pressure. I can guarantee you won't like the result.

(3) The pressure on the sidewall is certainly the safe maximum and you don't want to go over that, but I'm convinced the pressure on the door-jamb sticker on my car is too low. My wheels have been checked and re-checked for proper alignment, caster, camber, toe-in, etc. etc., and yet the tires aren't wearing evenly. The tread in the center is still OK but the tread on the edges (both edges of all tires) is pretty much gone. Lacking any evidence of mis-adjustment, this says "underinflation" to me just as it would say "overinflation" of the tread center were bald while the edges were not. Next set of tires, I'm definitely going to try upping the pressure a bit, while still keeping it south of the sidewall maximum.


(4) Shoot for 32-35. It's what I've used for years on several different cars. If you're going on a long trip on divided highways, go for 35 and see what kind of mileage you get; if it's raining, though, you get better traction at lower pressure (for the same reason you get better mileage at higher pressure: contact area).
I like the last one, as it matches what I am doing. But it is not a particularly informed opinion, and may not take bad Indian roads into account.

Last edited by rks : 7th April 2007 at 14:28.
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Old 7th April 2007, 14:25   #7
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Quote:
Originally Posted by rks View Post
Nice topic. And a very controversial one, with probably as many opinions/practices as there are drivers. The carbibles website of Chris Longhurst is strongly biased in favour of overinflation. One point I would like to note is that even those who advise to stick to manufacturer's recommendation cite only grip and uneven tread wear as the reasons -- not that they fear a tyre burst due to overinflation. As for fuel economy, I read a website (which I am not able to locate) that during a fuel economy run for some company (Subaru?), some of the participants overinflated the tyres to 60 psi!!!. Again Chris Longhurst makes tall claims w. r. to fuel econony (up to 25% increase due to overinflation in his Subaru). Probably will vary from car to car and from driver to driver.

I personally have not found any uneven tread wear in my S322 tubeless tyres even after 12500 kms, despite keeping tyre pressures at 35 psi. And the grip is very good, at least in dry conditions. Probably advisable to go back to manufacturer's recommendation of 30 psi or maybe at most 32 psi for monsoon season. Ultimately, it is one's own experience that matters most -- there canot be a general rule due to the large number of factors involved (car, road, driving style,...).

Edit: @sreenivass and vid6639, do you have any references for the possibility of suspension damage due to overinflation. I specifically searched for this possibility, but could not find any. The roads in India are very bad and those who recommend overinflation probably do not take this into account, since they are mostly foreigners. But I did read that *underinflation* is bad for the suspension. And I do not agree with vid6639 that sidewall damage is more likely with overinflation. It is with underinflation, as sidewall flexes more. But possibility of tyre damage due to impact on stone/kerb increases with overinflation. You have to drive more carefully on bad roads.
My reference is service engineer at Anuroop (Fiat workshop Hyderabad), when I asked him 29 vs 32 psi he felt 32 psi is way over inflation for any conditions. The guy says under all conditions 28 is the recommended one. He mentioned higher psi can cause damage to lower arms.

My personal experience with under/ over inflation is as follows. I find the ride very good at 28 PSI and harsh at 30 psi. While I continued to maintain 28 psi I suspected more shoulder wear based on my visual inspection. I maintain 29-30 psi now. upon examining the wheel I can tell you the contact area is more in the center of the tire than on shoulders. center is more grey compared to darker shoulder strips. There seems to be marginally better feel of response with higher psi, but I can feel the suspension working a bit more now than before. I never felt suspension acting (read harsh metal parts) before with 28 psi.

I do see lot of material in Subaru groups for suggesting more inflation. Infact I read one where it says inflate to 10% less than tire rating. For a 175/65R14 82T Bridgestone S322 this turns out to be 44 - 4.4 = 39-40 psi, wont do any good to me at all. I suggest check the coloration on your tire to decide if overinflation has started causing uneven wear. Tire manufacturer recommendation seems a little higher than vehicle manufacturer's recommendation.
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Old 7th April 2007, 14:25   #8
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I just found out some interesting stuff. Maruti recommends 33psi for the WagonR and Zen Estilo. both have them have 13" bridgestone S322.

That basically means that 35psi isnt really overinflating the tyres.

rks, you need to be around 38psi for 5psi more overinflation.
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Old 7th April 2007, 14:48   #9
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Because Maruti wants their customers to be happy with mileage. They don't care if a car skids off the road and kills everyone. WAKE UP, PEOPLE!
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Old 7th April 2007, 14:56   #10
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Quote:
Originally Posted by v1p3r View Post
Because Maruti wants their customers to be happy with mileage. They don't care if a car skids off the road and kills everyone. WAKE UP, PEOPLE!
I agree with you because of my gut feel v1p3r. I suspect overinflating could cause skidding, but can not establish or quote it. I would never really overinflate because of my feel as quoted before.
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Old 7th April 2007, 14:56   #11
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Quote:
Originally Posted by vid6639 View Post
I just found out some interesting stuff. Maruti recommends 33psi for the WagonR and Zen Estilo. both have them have 13" bridgestone S322.

That basically means that 35psi isnt really overinflating the tyres.

rks, you need to be around 38psi for 5psi more overinflation.
Note that the Estilo and Wagon R have 145 size tyres as opposed to 155 for Santro. Probably that is one of the reasons for the higher recommended pressure. I imagine that the max allowed tyre pressure ought to be 44 psi for these tyres; if so 38 can be run, but I doubt if it would be advisable for either Wagon R or Estilo. If max. allowed tyre pressure is 40 psi, then 38 is clearly not advisable in any case.
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Old 7th April 2007, 15:59   #12
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Quote:
Originally Posted by rks View Post
Note that the Estilo and Wagon R have 145 size tyres as opposed to 155 for Santro. Probably that is one of the reasons for the higher recommended pressure. I imagine that the max allowed tyre pressure ought to be 44 psi for these tyres; if so 38 can be run, but I doubt if it would be advisable for either Wagon R or Estilo. If max. allowed tyre pressure is 40 psi, then 38 is clearly not advisable in any case.
Nope the Estilo and WagonR VXi both have 155's it's only the LXi models that have 145's. both are recommended as 33psi.

v1p3r, yeah your right about the manufacturer recommending higher than normal for better mileage. No use going by those numbers.

I was just saying that as people blindly follow the logic and to top it off if you overinflate based on manufacturers recomendation then god help you.
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Old 8th April 2007, 00:21   #13
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It is best to arrive at the ideal psi by experimenting. Different people have different needs.
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Old 8th April 2007, 04:13   #14
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I just swapped oe Goodyears 205/65/15R to 225/60/15
Michlien energys on my new inniva. the guy at the tyre shop
told me to maintain 33 in my tyres all round. I feel the tyres are overinflated
and the car seems bouncy. what would the correct psi be in
this case. also whn driving in hot concrete roads due to constant
friction, specially on cement roads, the psi tends to slightly icreasse
in the tyre. is it safe to derease the psi by say 2-4 pounds per tyre
keeping the hot increase in mind? Gurus?
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Old 8th April 2007, 04:39   #15
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IMO one shd always stick to the vehicle manufacturers specifications on tyre pressure.they know the braking and suspension best.
safety should never be traded off for increased mileage.
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