Fill Tire Pressure To What Tire or Vehicle Says?

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Originally Posted By: crazyoildude
This is my point i was trying to make everyone has a different way of looking at this and everyone has their own beliefs. Someone posted tire shops putting all different pressures into tires i personally believe if you have an old car in the early 90's and it specs 35psi on the door and you put tires that say for instance max.50psi it is absolutely ok to put 40psi in them when cold. tires have improved a lot since the 1990 era. When i put 35 psi in my old truck it drove like a Cadillac but my tires wore and being underpowered it would lug going up hills with a heavy load when i put 40psi it was much better in every way. But the real reason i brought this subject up was to see some peoples beliefs some don't agree with me and some do but how many vehicles are driving on the road with who knows what in their tires. I know my new car dealer puts in the maximum the tires allow and i have to adjust them when i get home.


You can put in how much ever air you like in the tires. There's really no wrong answer as long as you put all tires as the same pressure.

But generally speaking the number on the wall of the tire is the max PSI (or burst limit) will the tire blow out at that psi? I'm not certain (never tried) but they have the numbers their for a reason.

Most Eco modders use very high psi for the roll. Nothing really wrong with it just what are you looking for. I know a few people with Hondas that actually keep them low to improve the ride.

My car on the other hand sails like a boat down the interstate at 2k rpm the ride is to soft for my liking so I raised it. Might raise it even more since front tires seem to be getting uneven wear (not due to over inflation) just the weight of the front end.
 
Originally Posted By: 3800Series
You can put in how much ever air you like in the tires. There's really no wrong answer as long as you put all tires as the same pressure.....


First I think everyone would agree that 3 psi would be a wrong answer. Same with 300 psi. So there are wrong answers, and what we are trying to establish is what is the "correct" answer. I put that word in quotes for a reason I will explain later.

Originally Posted By: 3800Series
.....But generally speaking the number on the wall of the tire is the max PSI (or burst limit) will the tire blow out at that psi? I'm not certain (never tried) but they have the numbers their for a reason.......


There are 2 ways a tire will have words on the sidewall about pressure.

1) Max Load XXXX @ YY pressure. This is stating a relationship. Note, it doesn't say anything about a max pressure.

2) Max Load XXXX, Max Pressure YY. This does state the max pressure, but doesn't state anything about the relationship between the pressure and the load carrying capacity.

In both cases, this has to do with the tire and not the vehicle. Note that there is no recommendation here. As was stated earlier, a tire manufacturer doesn't not know what vehicle a tire is going on, so they have no idea what pressure to recommend - other than to defer to the vehicle manufacturer.

Side note: It is pretty common for the sidewall of a tire to include a note about not exceeding 40 psi during the mounting process. This only applies to the mounting process. Again, this is not a recommendation.

Originally Posted By: 3800Series
.......Most Eco modders use very high psi for the roll. Nothing really wrong with it ..........


I thoroughly disagree with that. But it's a long argument and I won't bore you guys with it.

*******************

Also, there have been some changes since the 1990's. First is the Ford/Firestone thing. The lesson out of that was that the pressure listed on the vehicle tire placard was too low for trucks and SUV's. This had to do with load carrying capacity and nothing else.

Since that time, vehicle manufacturers have increased the tire size to get a larger load carrying capacity.

But cars weren't affected by that. They already were over specified - although many car manufacturers took the opportunity to review their procedures for setting the tire size / inflation pressure.

*******************

Ok, back to the "correct" answer.

I know that using the pressure listed on the vehicle tire placard gets you where the vehicle manufacturer tested. Yes, tires do vary as to how they feel - considerably. And, yes, there are tires out there that feel awful at the vehicle placard pressure.

So as a baseline, we can say that the pressure listed on the vehicle tire placard is specified such that the load carrying capacity of the tire is adequate. The sway bars, springs, and shock settings are specified around that pressure to get the handling feel the vehicle manufacturer decided it wanted.

So I think the vehicle tire pressure lists the "correct" pressure, but I call it the "specified" pressure as that is what it is. The fact that the specified pressure results in a ride or handling a person doesn't prefer is just a personal preference.

But because tires can affect the ride and handling of a car - and because it is much more difficult to change the springs, sway bars, and shocks - it is pretty common for folks to adjust the inflation pressure to a setting they "prefer". This would be different than "correct" or "specified".

I advise folks to use the vehicle tire placard pressure if there is no additional information provided. I will grant that earlier vehicles might need a few more psi to have the same reserve capacities currently being used - and to get a slightly different feel - but bo more than 5 psi. (and all this is assuming the tire size is the same as listed on the vehicle tire placard.)
 
Originally Posted By: crazyoildude
I know my new car dealer puts in the maximum the tires allow and i have to adjust them when i get home.


Incompetent dealer wrenchers...

The advice above (somewhere) that increasing pressure 2psi at a time is a starting point....increasing PSI effects ride (stiff/soft), performance (straight ahead stability in dry and wet conditions, traction and break-away limits on curves), and tire-wear and differs with each car....so such a 'test' is advised...Max. psi on the tire-wall is for maximum load in the car, an atypical, rare situation under most circumstances.
 
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Originally Posted By: Quattro Pete
Originally Posted By: Kuato
So OP short answer: start with what is on the door jamb. If you want factory ride and don't care about tire wear, leave it. If you want tires to wear evenly, adjust as necessary.

Not sure I follow your logic. In my experience, the wear is the most even at factory recommended PSI. If I increase PSI above that in my 530i, I get uneven wear.



Obviously BMW does a better job of matching suspension to correct tire pressures from the factory. See MrQuackers' post 3-4 down from yours for an experience similar to mine.

For the life of me I don't understand why a manufacturer would list such a low pressure, that causes increased wear and allows the tire to roll over in a corner, just for straight line ride quality. They shoukd do it the BMW way, have a full contact patch and even wear, and adjust the car to match.
 
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Originally Posted By: Kuato
Originally Posted By: Quattro Pete
Originally Posted By: Kuato
So OP short answer: start with what is on the door jamb. If you want factory ride and don't care about tire wear, leave it. If you want tires to wear evenly, adjust as necessary.

Not sure I follow your logic. In my experience, the wear is the most even at factory recommended PSI. If I increase PSI above that in my 530i, I get uneven wear.



Obviously BMW does a better job of matching suspension to correct tire pressures from the factory. See MrQuackers' post 3-4 down from yours for an experience similar to mine.

For the life of me I don't understand why a manufacturer would list such a low pressure, that causes increased wear and allows the tire to roll over in a corner, just for straight line ride quality. They shoukd do it the BMW way, have a full contact patch and even wear, and adjust the car to match.

My '95 Integra GS-R came with a 35/33 PSI recommendation on the door jamb, and I set it to that on every tire that I had installed. It was pretty well suited to the suspension and the typical driving style.
 
Originally Posted By: KitaCam
Originally Posted By: crazyoildude
I know my new car dealer puts in the maximum the tires allow and i have to adjust them when i get home.


Incompetent dealer wrenchers...

The advice above (somewhere) that increasing pressure 2psi at a time is a starting point....increasing PSI effects ride (stiff/soft), performance (straight ahead stability in dry and wet conditions, traction and break-away limits on curves), and tire-wear and differs with each car....so such a 'test' is advised...Max. psi on the tire-wall is for maximum load in the car, an atypical, rare situation under most circumstances.


If that's true I'd dump that dealer.
 
The recommended tire pressure on the door placard should be the starting point for tire pressure. And for most people, this should be the pressure they use all the time, as they can't "feel..." their car anyway... nor do they inspect their tires for uneven wear. So run what the car maker recommends.

On my cars, I like to experiment... but I start at the door sticker psi, and never go below it.

On my Honda Odyssey van, the sticker says 33 front, 35 rear. Seems weird, as the van is FWD , with a huge lump of engine/tranny sitting on the fronts... Sure enough, the van eats the front outside tire shoulders. FWD, zero camber and some body roll . I bumped up the pressure to 38 front, 35 rear, and the ride firmed up a little, steering is more responsive, and the tires wear much more evenly.

The factory setting seems sharply biased towards ride comfort, at the expense of tire wear and handling. And in my experience, most factory tire pressure recommendations do favour ride over handling and responsiveness.

I have run tires at the max psi on the sidewall though, and nothing bad seems to happen. The tire is designed to run UP TO the max pressure, so its not gonna blow up or anything. It will ride much harsher, though, and may wear more in the middle. Steering responsiveness is very good, but overall grip seems to fall off a bit.

Note: If you plan on heavily loading your car , and running at sustained high speed on a really hot day, then the tire max psi might be your best choice...
 
Originally Posted By: Bear

If that's true I'd dump that dealer.


Yes. That dealer obviously has a moron-friendly hiring policy.

The only time I don't follow the door placard is when I drive one of my cars on the track- and even then I usually don't deviate from the recommendations by more than 2-4 psi.
 
Originally Posted By: geeman789
On my Honda Odyssey van, the sticker says 33 front, 35 rear. Seems weird, as the van is FWD , with a huge lump of engine/tranny sitting on the fronts


Quote:
If a car is understeering, it means the car turns less into the corner than it should for the steering input. So obviously, the rear tires, which want to go straight have more grip than the front tires which are trying to turn. To solve this problem we can increase the contact patch of the tires that need more help. That means lower pressures on the front, or we can decrease the contact patch size on the tires that have too much grip, so increase rear pressures.

For oversteer or loose handling, the front tires have more grip and the car’s back end can’t keep up. So now, we need to increase front tire pressures to make the contact patch smaller (less grip) or decrease rear tire pressures to make the rear contact patch bigger (more grip).
 
Originally Posted By: Warstud
Originally Posted By: geeman789
On my Honda Odyssey van, the sticker says 33 front, 35 rear. Seems weird, as the van is FWD , with a huge lump of engine/tranny sitting on the fronts


Quote:
If a car is understeering, it means the car turns less into the corner than it should for the steering input. So obviously, the rear tires, which want to go straight have more grip than the front tires which are trying to turn. To solve this problem we can increase the contact patch of the tires that need more help. That means lower pressures on the front, or we can decrease the contact patch size on the tires that have too much grip, so increase rear pressures.

For oversteer or loose handling, the front tires have more grip and the car’s back end can’t keep up. So now, we need to increase front tire pressures to make the contact patch smaller (less grip) or decrease rear tire pressures to make the rear contact patch bigger (more grip).


The vehicle in question is a FWD mini-van... it UNDERSTEERS... PERIOD...!

Tire pressure changes are rarely enough to dramatically change handling, fine tune, yes, but change an understeering car to an oversteering car, never seen it happen...

On snow / ice, I can get the van to oversteer by braking hard then doing a scandinavian flick... gets the back end light , then rotates....

The stability control HATES it when I do that...!
 
Ha Ha, and this all from a retired electronics dude.. Thanks for your opinion Im going to stop here because i am a gentleman.
 
Originally Posted By: crazyoildude
Ha Ha, and this all from a retired electronics dude.. Thanks for your opinion Im going to stop here because i am clueless.
 
Originally Posted By: Taildragger
Originally Posted By: crazyoildude
Ha Ha, and this all from a retired electronics dude.. Thanks for your opinion Im going to stop here because i am clueless.




Hardly necessary bud.

Because he chose to stop before becoming obtuse you reduced yourself to this kind of nonsense.

I've seen plenty of arguements on this site,all fought with vigour and many good points were made,and the thread was informative.
When reducing oneself to name calling shows much about said person,and perhaps this isn't a forum for you.

Just sayin.
 
Originally Posted By: Clevy




Hardly necessary bud.

Because he chose to stop before becoming obtuse you reduced yourself to this kind of nonsense.

I've seen plenty of arguements on this site,all fought with vigour and many good points were made,and the thread was informative.
When reducing oneself to name calling shows much about said person,and perhaps this isn't a forum for you.

Just sayin.


Well stated,excellent point. When I started reading this thread I was sure OP was trolling. It appears not. Now if some of the valid points from this thread will sink in it is a win win for all.
 
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Living where I do, the horrorshow of the South, with badly paved streets and potholes that are old enough to have birthdays, I prefer a comfortable ride. But I have learned here not to go below the door placard tire pressure.

The Regal, which is a sporty-ish sedan, calls for 33 psi all around. I do 34, which gives me a little better handling, but isn't rough-riding. When I drove all highway to Amarillo, TX, in May, I bumped them all up to 36.

The Michelins have -- and I'm guessing without looking -- 44 psi as the maximum. If I pumped them up to that, I'd be rattling my teeth on these streets.
 
I wonder how many tire gauges out there are actually accurate. I bet many are +- 5-10 psi. Then a temperature difference from morning to evening can make quite a bit of difference, too.
 
Originally Posted By: datech
I wonder how many tire gauges out there are actually accurate. I bet many are +- 5-10 psi.

I've got many gauges, cheap and more expensive. They all read within 1 PSI of each other.
 
Originally Posted By: Quattro Pete

I've got many gauges, cheap and more expensive. They all read within 1 PSI of each other.


Same here...
 
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