Tires/Proper tire pressure for bigger, aftermarket tires
I have an '03 F-150 4- door crew cab and have upgraded the tire size from the stock, LT265/70 R17, to aftermarket BFG All-terrain LT315/75 R16 load range D. Im not 100% sure of the proper tire pressure to use to wear the tread evenly. If you have any suggestions, that'd greatly be appreciated. Thank you
There are 2 schools of thought.
1) match the load carrying capacity
2) If there is the same of more load carrying capacity, match the inflation pressures.
Let's do #1:
On every vehicle sold in the US, there is a vehicle tire placard which lists the original tire size and the proper pressure for that size. Since 2008, the placard is supposed to be on the driver's door frame, but prior to that it could also be in the glove box, on the fuel filler door or on the trunk lid. For as long as I can remember, Ford has been putting the placard on their trucks on the driver's door frame. Go look and see if what follows is correct.
According to Tire Guides, the vehicle tire placard for a 2003 Ford F-150 Crew Cab with LT265/70R17's would say the inflation pressure is supposed to be ........ Well none of the versions I see came with T265/70R17's. There is quite a few variations here: 4X2, 4X4's, Lariat's XLT's, etc. And none of them list an LT265/70R17.
But there is a version that has P265/70R17 (and 32 psi front and rear) and I am going to assume that is what your vehicle says. Please check, because everything I quote from this point forward will depend on that inflation being correct.
So the load carrying capacity of a P265/70R17 at 32 psi is 2205#. In order to carry the same load, an LT315/75R16 needs to use ...... well, the charts don't go below 35 psi - and I think that means those kind of tires should be used below that pressure - even if it means unusual wear.
So even though the load carrying capacity is adequate, I don't think you can do #2.
Also, inflation pressure isn't the biggest factor in even wear. Wheel position (as in drive vs steer) had more effect. Drive tires tend to wear in the center and steer tires tend to wear in the shoulders and regular rotation will even the wear out - and that is more important than inflation pressure.