Quote:
Originally Posted by CapriRacer
Let me put it like this:
Tires on the 1997-1999 Ford Explorer: *
P235/75R15 @ 26 psi = 1594# = size in question!!
P225/70R15 @ 30/35 psi = 1475#/1594#
P255/70R16 @ 30 psi =1913#
Tires on the 1997-1999 Chevy Blazer:
P205/75R15 @ 35 psi = 1452#
P235/70R15 @ 32 psi = 1643#
* - Tire load carrying capacities at the pressure specified INCLUDING adjustment for use on an SUV.
Please note that the load carrying capacity of the tire in question is NOT the lowest value.
I didn't show other vehicles, nor do I have the GAWR's, but at the time (Fall of 2000) I did ALL of the vehicles and had access to the GAWR's (which I don't now) and I gave that information to our VP of quality for the tire manufacturer I worked for. I was asked to do this to be sure we knew what was going on - particularly since Firestone was pointing out the pressure issue. Looks like they did a good job of obscuring the facts as the argument continues to sway people even 20 years later.
What did come out of this analysis was that - using our own data - certain tire combinations showed NO returns for the same time period - and those returns had one thing in common = H and higher speed ratings.
Our conclusion at the time was that it wasn't the pressure on the Ford Explorer that was the issue. I wasn't in a position (at the time) to know what the issue was (somebody in our organization did!), but I later found bits and pieces on the internet to get enough to make a coherent story - which lead me to write up the webpage I cited above.
So for 20 years I have been saying that the pressure was not the issue and the combination of the design of the tread pattern and the way the plant processed the rubber WERE the issue. This is also what the government (NHTSA) found.
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I ran the calculations using the formula posted elsewhere in this forum, assuming original size tire on a 2WD 1997 Explorer(using GAWRs from the placard image in the Barry's article you linked to).
Specifying the 2WD 1997 Explorer on TireRack, the recommended tire is 235/75R15, 105T, Max load 2,039lbs at Max cold pressure 44psi:
FRONT = 2,510/2 = 1,250/2,039 * 44psi = 26.97 cold (27)
REAR = 2,900/2 = 1,450/2,039 * 44psi = 31.28 cold. (31)
So the formula suggests significantly higher rear cold pressures, and only a slight bump up in the front pressures, presumably to maintain steering feel.
Most large legacy rear-drive vans(think: Econoline, Express, B2500), run at least that front-rear difference, if not at least 20psi higher rears than fronts.
I still implicate the low pressures on those Explorers as at least 60% of the culprit in those tread-sep/blow-out cases. Those cross-section photos(Figure 9) in the Barry's article could have been of any tire, from any vehicle or tire mfg. We'll never know definitively.