Tires: Tire Pressure, recommended pressure, doorpost

Question
Mr. Smith,

Having a heck of a time finding the right answer, so hopefully you can help.

I have a 2008 Wranger Unlimited Rubicon that I went a few sizes up on the
tire and the dealer way under-inflated, but said was right.

The placard says recommended is 260 kPa 37psi.  The original tire size was
LT255/75R17 C....

I now have the Nitto Terra Grapplers LT295/70R17 with a cold recommended
pressure of 65 psi, which sounds way to high.  Just trying to get your
thoughts on this.  The dealer originally inflated these at around 35psi, which
triggered the low tire alarm.

Thanks, Todd

Answer
Todd,

First let's talk about the triggered low tire alarm.  I'm hoping you realize that the pressure sensor doesn't care what tire it is mounted in, nor does it care what the pressure is supposed to be - all it cares about is if the pressure drops below a preset amount - which apparently is 35 psi.

But the second thing is that the Nitto's do not have a recommended pressure - only a maximum - at 65 psi.

I do not yet have my book for 2008 models (due out momentarily), so let's assume your figures are correct.

AN LT255/75R17 at 37 psi has a load carrying capacity of .......wait a minute.....none of my books show either of those sizes.  I'm guessing the 2008 versions of these books will (also due out momentarily) - but what to do? What to do?

If I take some educated guesses, I think I can guesstimate that an LT295/75R17 would need about 27 psi to carry the same load.  Hopefully that will not be too soft.

(unless of course the tire sensor is an indirect one, and in that case it shouldn't matter, so long as the pressures are the same.)

The key to the right pressure is matching the load carrying capacity of the original tire size and the proper pressure for that size - and both of those are on the vehicle placard which is usually located on a doorpost or in the glove box.