Auto Tire pressure

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  #1  
Old 02-14-06, 08:42 AM
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Auto Tire pressure

My mechanic insists on over inflating the tires in my 2003 Honda Civic he feels if the max pressure on the tire says 50 lbs you should put in about 6-7 lbs less I say BULL for general all around driving I go with what it says on the car door 32 in front and 30 lbs in rear Who is correct?
 
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Old 02-14-06, 08:56 AM
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Can't really go wrong with the plate on the door. That said, my tires have a max pressure of 44 psi and I like to keep them at 40.
 
  #3  
Old 02-14-06, 09:20 AM
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Going with the auto-maker recommendations is the best course

I also adjust the pressure around the recomendations on my work van depending on load and expected use
But I mean like I'm going a few K miles with it empty or loaded to the max
For all around it's the door plate
 
  #4  
Old 02-14-06, 11:18 AM
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Ditto on the door plate. The suspension etc is designed for that cold pressure.
 
  #5  
Old 02-14-06, 04:38 PM
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Originally Posted by seacilian
My mechanic insists on over inflating the tires in my 2003 Honda Civic he feels if the max pressure on the tire says 50 lbs you should put in about 6-7 lbs less I say BULL for general all around driving I go with what it says on the car door 32 in front and 30 lbs in rear Who is correct?
Go with what feals best in handling and ride . If door plate gives this go for it.
 
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Old 02-14-06, 06:32 PM
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Originally Posted by seacilian
My mechanic insists on over inflating the tires in my 2003 Honda Civic he feels if the max pressure on the tire says 50 lbs you should put in about 6-7 lbs less I say BULL for general all around driving I go with what it says on the car door 32 in front and 30 lbs in rear Who is correct?

Yeah 30 to 35 used to be the norm but not anymore go with whatever the tire says or a little less if you want.
My goodyear a/t wranglers have a max 60 psi, my trailer tires a 50 psi, I always keep above 40 at least , never had any trouble whatsoever.
 
  #7  
Old 02-15-06, 06:21 AM
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The problem with going with the door plate pressure is that it presumes that you have the same size/type/rating/etc trire that the manufacturer put on the car, which is probably optimal, but very few people put the exact same tire on as oem. Go with the pressures listed on the tires themselves. Adjust the pressure as desired for the ride you prefer, but somewhere between the max pressure listed and max pressure minus about 20% or so, i.e. a 44 psi rated tired would be 36-44. If you have tires rated at 50 psi and you are driving them at 30-32 they are way underinflated (and the tire companies will probably send you Christmas cards )
 
  #8  
Old 02-15-06, 09:00 PM
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"Maximum Inflation Pressure is the highest inflation pressure that the tire can withstand. This is not, however, the recommended inflation pressure. Inflation pressures should never be below the recommended pressure or above the maximum pressure branded on the sidewall."
http://www.1010tires.com/tech.asp?type=tires

Like the volume of a tv set
Just because it has a maximum of lets say 0 to 50, we do not use 50
We turn up our volume to a value that is good to us and our surroundings.
Tires are like that. Just because the maximum amount is stamped on the tire we should not use it
We put just enough air in the tires that is right for our car.
That is figured out by the auto engineer.
That figure is then put on the piller on the drivers side door.
 
  #9  
Old 03-23-06, 04:11 PM
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As a former chassis engineer for General Motors Corporation I can assure you that the cold inflation pressures that are usually listed on a label on a door or door opening is where you need to inflate your tires to. The pressure listed on the tire is the maximum pressure and weight rating that a tire can handle. Anyone using that pressure rating and inflating the tire to anywhere near that pressure is just plain WRONG! Now if you are seriously over loading a car, truck or trailer then additional pressure can be advisable but that is not what we are talking about here. Some of the folks that have replied here are opening themselves up for very harsh rides and tire, wheel and suspension failures. My advise is doen't try to re-engineer the vehicle and go with what the manufacturer recommends, after all they spent millions of dollars testing the performance of the vehicle.
 
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Old 03-23-06, 07:45 PM
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So I should inflate my donut spare to what the door jamb sticker says?

Personally I've always run my tires at or near the maximum and I've never had a harsh ride or tire, suspension, or wheel failure. Of course, I've mostly owned Toyotas..........
 
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Old 03-23-06, 09:36 PM
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Running tires at the pressure on the door plate was what caused the tread separation problems on ford explorers with firestone tires a few years ago, the pressure listed on the door was too low to be safe.
 
  #12  
Old 03-23-06, 11:39 PM
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if you beleive firestone's reason for the failures, personaly I think the tires was defective, dont really expect a tire to come apart even if it is ran 5 to 10 psi low, there is alot of vehicles on the road that has atleast one underinflated tire, my point is tire seperation would be alot more common if that is all it took.
 
  #13  
Old 03-24-06, 07:10 AM
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Steve, the Firestone/Explorer debacle has cast doubts on many car owners with the reasoning behind the recommended tire pressures given by the manufacturer. For the Explorer, Ford recommended a pressure that was not in the best interest of the tire and its performance, but to lower a center of gravity to meet certain Federal static rollover tests. Now wary owners are second guessing the manufacturer's recommendation and perhaps adding a few pounds of pressure.

This in no way reflects badly on you, Steve, as a chassis engineer. I too am an automotive engineer, and I like to think the blame usually rests on the managers who, despite the good information provided by the engineers, make decisions that are purely political or poor economics.

BTW, your comment on people reengineering vehicles weighs heavily with me. I see people talking about putting larger rims or increasing wheel offsets, and are completely oblivious to the negative (and sometimes dangerous) effects this will have on vehicle performance.
 
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Old 03-24-06, 07:32 AM
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IMHO the tire pressure should be adjusted for best tire wear. Often the sticker on the door recomends pressures so low that the tires wear on the outside. I always run more than the auto/truck manufacture recomends and never have any problems. I like to replace my tires when they are worn out evenly, I feel like I haven't got my moneys worth if they are bald [or worse ] on the edges but have plenty of thread in the middle. Too much pressure and they will wear down the middle but very seldom have I ever seen that.
 
  #15  
Old 03-24-06, 08:48 PM
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Remember cold tire pressure expands with tire speed and that 30-40 psi gos to 10- 20 more psi and tire can fail if tires are old or have weak spots in then. (This is just my opinion.)
 
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Old 03-24-06, 09:28 PM
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just go with whatever tire says

inflate to or a little less to what the tire says for max inflate psi cold, pressure is not suppose to go up too much with speed unless tire is overheating due to excessive wear ,good thread circulates air on tire surface thus keeping tire cool. avoid cheap tires too
 
  #17  
Old 03-25-06, 05:53 AM
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I have been using Goodrich tires on my truck at 35psi and I am starting to see the interior tread wear faster than the outside. I don't know how all of you who run 40 psi in a tire get any life out of your tires. I set my psi back down below 32 on this truck to extend the life of these expensive tires.

Any financial economies that you save in mpg by going with a higher psi setting get offset by the purchase of new tires quicker than what you would normally need.
 
  #18  
Old 03-25-06, 02:07 PM
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Here is what some EXPERTS say about tire pressure. SOME of you will benefit from reading it.
From http://safercar.gov/tires
Manufactures of passenger vehicles and light trucks determine tire pressure specs based on vehicles design load limits and the tire size. The proper tire pressure for your vehicle is referred to as "recommended cold inflation pressure". Remember, the correct pressure for your tire is what the vehicle manufacturer lists on the placard, NOT what is listed on the tire itself. Because tires are designed to be used on more that one type of vehicle, tires list the "maximum permissible inflation pressure" on the tire sidewall. This is the greatest amount of air pressure that should ever be put in the tire.

Also from the same site, step 1 for maintaining proper tire pressure is: "Locate the recommended tire pressure on the vehicle's tire information placard, certification label, or in the owner's manual"
Step 3 indicates you should let out any excess pressure.

From http://www.uniroyal.com
This site says, "You should ALWAYS use the inflation recommended by the vehicle manufacturer."

From http://www.michelinman.com
Under Recommended Pressure it says, "Always inflate your tires to the recommended pressure listed by your vehicle manufacturer."

From http://www.rma.org
Some quotes from the subject "Inflation Pressure".
"The "right amount" of air is the pressure specified by the vehicle manufacturer,......"
"The correct air pressure is shown on the tire placard attached to the vehicle........."
"Motorists are strongly advised to follow the vehicle owners manual or the tire placard in the vehicle for proper inflation and loading"

So, there it is for those of you who think you know more than the Goverment, Tire Manufacturer, Vehicle Manufacturer and the Rubber Manufacturers Association. People look to this forum for correct information, not old "wives tales" gut-feelings and "I must be right because this is the way I've always done it and it works for me" type attitude. There, now I feel better!!!
 
  #19  
Old 03-25-06, 09:25 PM
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Originally Posted by HairyKnuckle
I have been using Goodrich tires on my truck at 35psi and I am starting to see the interior tread wear faster than the outside. I don't know how all of you who run 40 psi in a tire get any life out of your tires. I set my psi back down below 32 on this truck to extend the life of these expensive tires.

Any financial economies that you save in mpg by going with a higher psi setting get offset by the purchase of new tires quicker than what you would normally need.

this is due to bad alignment/shocks , not tire pressure ,3 psi make no difference.
 
  #20  
Old 03-26-06, 10:09 AM
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Better just mark this post "agree to disagree". It's in the same category as "should I buy the $2/qt oil for my car or the $1.29 stuff" [and let's not go there].

And I'm sure the Goverment, Tire Manufacturer, Vehicle Manufacturer and the Rubber Manufacturers Association all thought Firestone tires on Ford Explorers were just peachy-keen.
 
  #21  
Old 03-27-06, 06:14 AM
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Originally Posted by LouBazooka
this is due to bad alignment/shocks , not tire pressure ,3 psi make no difference.
I can see an alignment issue being caused by one side of the tire wearing which would mean your camber was out. I can see the individual tread rows wearing to one side which would mean your toe-in was out of spec. I don't understand your comment about an aligment issue with the interior tread of the tire wearing. That is an overinflated tire issue....

My vehicle has 30k mile on it, I don't see how I could have bad shocks on this vehicle yet with the issue on all 4 tires.
 
  #22  
Old 03-27-06, 07:08 AM
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When you say interior tread, do you mean the inside edge of the tire or the center of the tire? The word 'interior' is ambiguous.
 
  #23  
Old 03-27-06, 07:17 AM
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Originally Posted by Kestas
When you say interior tread, do you mean the inside edge of the tire or the center of the tire? The word 'interior' is ambiguous.
The middle tread of the tire (center).

I also thought cupping on the tire was an indication of bad shocks, not center tread wear.
 
  #24  
Old 03-27-06, 08:00 AM
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HairyKnuckle
If the center of the tread is wearing more than the rest of the tire and it is wearing evenly I would suspect the tire is over inflated. Set your cold pressures to what the label on the door or door opening says and the wear should even out over time.
 
  #25  
Old 03-27-06, 10:02 PM
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I kinda agree with the chassis builder a bit. From my experiences indy car, champ car, and F1 do not run 50PSI this I know from 1st hand unfortunately (crappy pro racing stuff they don't come close to that pressure). I personally am running 5psi from manufacturers pressure becuase it feels way way better for handling. My door recommends 29 psi. You want to talk about side way roll at 29psi lol; my recommendation is that I have not driven a vehicle that I would set above 7psi from manufacture's spec on the door which I base off the response of many vehicles and tire pressures that I have tested and so far I have never exceeded 7psi (over door spec from manufacturer) to max out my times in a slalom and breaking.

Put it this way if you are in the mid 30's your doing ok. ( for a regular passenger vehicle)
 
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