The "correct" tire pressure --- NOT A SCIENCE!!!!

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Originally Posted By: crinkles
follow the door placard... we do not know more than vehicle manufacturers or auto engineers...


You very fortunate that you have factory automotive engineers that know how you drive, what conditions you drive under and what kinds of loads you carry so they can put the best pressures for your personal use on the placard.
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Us mere mortals don't get that level of service.

Then there's the little problem that the numbers on the placard aren't necessarily what the engineers wanted.
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I know I just drove through some good thunderstorms this evening with tires at sidewall maximum, and experienced no hydroplaning, even with I-95 resembling a canal at times.

Of course, driving at a reasonable speed helps too.
 
My cousin's husband runs theirs at MAX pressure all year. In winter they are like hockey pucks, with the grip to match. She complains that she can't even get into a plowed driveway, but commutes 60+ miles a day on country roads.

I tried to tell them to adjust the pressure, but as most advice, it falls on deaf ears unti they hear it on TV.
 
I believe one has to also look at the replacement tires you may have purchased. Some OEM tires are max cold pressure at 35 PSi and the door placard is based upon that. Now you get a tire with a mAX PSI of 44 and IMO I increase the pressure.

I have found that the best mileage out of my tires (especially from wearing on the outside edges on the front) is to keep them near the max cold pressure. Thus my max 44PSIs get around 42 cold. Best wear for me with a very slight harsher ride. Some tires are now also max PSI of 50. If the door placard says run at 28 IMO you would be running an underinflated tire, well,not underflated but would not get the best mileage out of it
 
The Ford-Firestone failures are the perfect example of why I rarely keep oem tires on anything, especially up here since road conditions are so poor. Load capacity had far less to do with the failures, a cheap, poorly built tire with owners rarely if at all checking the vehicle's tire pressure or even looking at them, is the combined fault. I am amazed how many people drive on failing tires, I'm always pointing out separations, low pressures, sidewall bulges, lack of tread, etc.

OEM tire pressures are not for handling, milage, comfort, even tire wear, they are defining where you should be fully loaded to the vehicle's capacity. My older super duty spec'd 70psi rear, empty or loaded. Rediculous, ride and tire wear would be horrible when empty, but it protects the manufacturer if I run less psi while fully loaded and have a tire separate.

I've used a huge span in tire psi with various vehicles, 10 ply tire on a f150 doesn't make traction worth beans if you use the 35psi fr/rr rating in the winter, an '03 windstar running 35psi on oem uniroyals look like they are running an inch of sidewall on the pavement, and feel that way too.

Many different factors define proper psi, what is on the door may or may not be the best recommendation, but it is sure hard to get around the stupid low psi warning systems in all the new vehicles now while trying to find optimum psi, LAME!!!!!
 
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I ran my tires at max sidewall pressure visiting family in upstate New York this past winter, and found the grip just fine. YMMV.

Also aired up the tires to max sidewall (44 psi) in the fiancee's Fit, and it rolls forever now. Also handles a bit more crisply, and if anything the suspension felt better.

But that's me. YMMV.
 
Originally Posted By: Jason Adcock
This is interesting. I've played with inflation pressures on my own '07 Corolla (using the stock 195/65R15 size), and actually find that I like the OE 30/30 best (which is unusual for me). Increasing inflation pressure quickly added ride harshness, and I actually get best fuel economy at the OE pressure spec. On my minivan, it specs 36/36, and I run them at about 38/36.


+1. I had my 05 camry at 35 psi for a while (OEM recommended is 30 psi).

ride at 30psi is MUCH MUCH better than at 35. like a different world. fuel consumption - unaffected
 
Originally Posted By: Spector
Thus my max 44PSIs get around 42 cold. Best wear for me with a very slight harsher ride.


Wow - I change mine from 33 to 35 and I can feel it in less than 6 blocks.
 
My DD OEM specs are 30 psi front and 36 psi rear. I run 40 psi all around. My Highway car factory spec is 36 psi all around and I run 42 psi all around. I tried running them at 44 psi max side wall and they were squirrelly in the rain. No hydroplaning just a little too responsive for me in the wet.
 
Originally Posted By: XS650
Then there's the little problem that the numbers on the placard aren't necessarily what the engineers wanted.
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At least on the door jamb of my folks' 2001 Camry, there's a recommendation for 32 lbs front/rear cold pressure fully loaded, and 29 lbs front/rear cold pressure up to a limited amount of loading.

Unfortunately the door jamb numbers don't account for non-OEM tires, different sized tires, (usually) loading, different driving styles, etc. I do remember my 1995 Acura Integra GS-R with rather high recommendations for 35/33 lbs front/rear. I actually kept it around those numbers because they weren't exactly tuned for a "soft ride". I think those numbers were well suited for the vehicle, while other cars have their recommendations tuned for a more compliant ride.
 
Originally Posted By: ALS
My DD OEM specs are 30 psi front and 36 psi rear. I run 40 psi all around. My Highway car factory spec is 36 psi all around and I run 42 psi all around. I tried running them at 44 psi max side wall and they were squirrelly in the rain. No hydroplaning just a little too responsive for me in the wet.


That's interesting; when I had my Corolla's tires at 35 PSI all around (OE is 30 PSI on all 4), the rear end felt a little "skatey", even on dry. Maybe squirrelly is a good description. I didn't really care for it. It feels better planted at 30 PSI.
 
I've experimented a lot with pressure, too, and have come to find that the recommended pressure is usually too low. Optimal for the cars I've recently owned seems to be 3-7 psi over spec, but always under max sidewall pressure.
 
Another thing to consider is the max allowable pressure for the wheel. I have some wheels that are only rated up to 36 psi cold.

I agree with other posters, I prefer 2-3 psi over the recommended pressure.
 
Originally Posted By: Junior
Another thing to consider is the max allowable pressure for the wheel. I have some wheels that are only rated up to 36 psi cold.

By "wheel" do you mean the rim on which the tire is mounted? I've heard of wheels having a specific max weight limit, but not pressure...
 
Originally Posted By: Quattro Pete
Originally Posted By: Junior
Another thing to consider is the max allowable pressure for the wheel. I have some wheels that are only rated up to 36 psi cold.

By "wheel" do you mean the rim on which the tire is mounted? I've heard of wheels having a specific max weight limit, but not pressure...


Yeah, I have 2 piece welded aluminum wheels. The center wheel is welded to the rim, the rim supports the tire. When I bought them there was a warning about not inflating over 36psi cold.
 
I jack my 32psi-rated tyres up to 40psi. Like the slightly stiffer ride, and I'm sure it gives me an extra few MPG.

The door sticker is to protect the manufacturer from extreme conditions, ie: some dodo that drives in the +120degF heat, at maximum gross weight, and travelling 100+mph, from tyre failure.
 
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