QuestionWhat should the tire pressure be on Firestone Wilderness P265/70R16 mounted on a '91 Chev K-1500 4-wheel drive P/U?
AnswerFrank,
According to Tire Guides, a 1991 Chevy K1500 originally came with 1) LT225/75R16's mounted on 6.5" rims inflated to 50 psi front and rear, 2) LT245/75R16's mounted on 6.5" rims inflated to 50 psi front and rear, or 3) LT265/75R16's mounted on 6.5" rims inflated to 50 psi front and rear. This all depends on the load carrying capacity of the vehicle.
Please check the placard on your vehicle because what I am about to write depends on this information being correct. The placard will list the original tire size and the proper pressure for that size. The placard is usually located on a doorpost or in the glove box – but sometimes it is located in the trunk or on the fuel filler door.
Looking at what Tire Guides says, I can see a problem. An LT265/75R16 requires a minimum of a 7" rim. So either the rim quoted by Tire Guides is incorrect or the LT265/75R16 did not come on the truck. I suspect the there were some 7" rims in the mix somewhere.
Also, a P265/70R16 also requires a minimum of a 7" rim. I should point out that using a rim width that is too narrow will tend to arch the tread face, making the vehicle tend to follow the ruts and grooves in the pavement and the vehicle will feel (and be) a bit unstable. I hope Tire Guides is wrong about the rim width, but it important to check.
But let's assume for the moment that you have the smallest tire (and the smallest load carrying capacity truck). Then a P265/70R16 needs to have 27 psi to carry the same load.
If the original tire size is LT245/75R16, the a P265/70R16 doesn't have enough load carrying capacity to match the original load carrying capacity - and this would be also true for the LT265/75R16.
It is now very important that we establish what the placard says was the original tire size, and what the rim width is that is being used on the truck.
