air pressure question

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I use the placard recommendations, especially if I have the same size and type of tire on the vehicle as stock.

On my truck, I did some homework when I switched tire sizes and went from a P-series tire to an LT Load Range C tire with a Max inflation pressure of 50 psi. I actually figured what the derated load carrying capacity of the OEM tires were (remember that P-series tires must have the their weight rating derated approximately 10% when used in light truck applications), then pulled the Bridgestone Light Truck Tire guide, and matched pressures. The OEM for my truck was 35f/35r, while with the new size and LT series tire, the same weight is carried at 38f/38r. 25,000 miles later and no wear problems to report...
 
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Originally posted by JohnnyO:

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Originally posted by Matt-TDI:
This also raises an interesting subject; the Ford/Firestone tire recall with the Explorer. I tend to believe that Ford was more at fault than anyone. They put P-rated tires standard on a 4,000+ pound vehicle. That's perfectly acceptable, but the tire placard in the driver's side door says to inflate to only 26 PSI! Getting away with that pressure on such a heavy vehicle would require an LT-rated tire, not P-metric, IMO. Otherwise raise the pressure. Also interesting to note is that I believe during the recall Ford was supposed to replace those tire placards with updated ones that read 30 PSI front and 35 rear maybe? I know the newer ones have that (note that Ford isn't the only manufacturer to recommend exactly 26 PSI for an SUV. Although most of the others that do recommend that are much smaller and lighter weight, like the Honda CR-V).

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The situation with the Exploder was that the rear pressure was set low to minimize rollover tendencies. OE recommended psi was 30f/26r. After the recall they put a new sticker on saying 30 all around. 26 is kinda low plus most of America goes around with underinflated tires on top of that.
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That said, the ONLY tires with a record of failure were Firestone Wilderness AT's size P235/75-15 built at one particular factory, which you could tell from the serial number. I had such a set on my 99 Ranger and got a free new set of Goodyears.
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Car & Driver did a test with a modified rim that they could quickly deflate by remote control, regardless of what they did at what speed, the Explorer didn't roll over when the tire went flat. This lends creedence to the theory that much of the populace simply doesn't know what to do when they have a blowout. (Oh my!
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A tire went flat, I must wildly swerve the steering wheel back and forth!)
There may be some evidence that Exploders with the full-time 4wd may have been more likely to lose control because the AWD would kick in, sensing differing wheel speeds but I'm not aware of any studies that broke those out separately. IMHO I think some fault lies with Ford and Firestone both.


Good points... I remember seeing that Car and Driver deal as well. The driver on one run demonstrated how much steering input was needed to control a blow out by taking both hands off the wheel and simply hitting the brakes fully, tires screeching and all. Even by hitting the brakes wildly like that, the vehicle exhibited no behaviour to indicate it would lose control, slide and maybe rollover.

I had totally forgotten about that test. Thanks for the memory refreshment and putting me back in my place
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And I see I'm not the only one who likes referring to Explorers as Exploders
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I'm glad I found this thread. I've been driving on underinflated tires. 35psi is what is on the door of my truck, max pressure on the tire is 44psi. I've had about 32psi.
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I just put 37psi in the rear and 36 in the front. I like a harder more responsive ride.
 
In cool weather, I stay at 40 pounds for a tire speced with a maximum pressure of 44 psi, and 33 pounds for a tire with max pressure rating of 35 psi.
 
The placard in my car says 32F/35R under normal driving conditions. The car is new and I followed these recommendations for a little over 12,000 miles. Upon switching to larger rims, I noticed the front tires wear pattern was excellent, but the rear tires were wearing mostly down the center. I called BMW of America and asked about using the placard pressure and the rear tires wearing out prematurely in the middle and they stated the placard is only a guide. Never inflate above the recommended max tire pressure printed on the tire, and to check wear and adjust pressure accordingly. They said it was possible the rear tires were wearing out a little prematurely because the inflation placard recommendations were for best performance, not longevity. I stand behind my prior comments as to using a very wide chalk line across the tread to view your wear pattern as evidence of proper alignment and inflation.
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Originally posted by Steel Blue Wind Rider:
I stand behind my prior comments as to using a very wide chalk line across the tread to view your wear pattern as evidence of proper alignment and inflation.
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I want to see what happens when I tell everybody that I am running BF Goodrich All Terrain TA LT265/70-16's (load range D) on my truck and I usually run 35 psi in the front & 20 psi in the rear. The only time the rear tires get more than 20 psi is when I haul something or pull a heavy trailer.
 
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