I know that you're suppose to inflate your tires based on the doorjam sticker and not on the PSI rating posted on the side-wall of the tire. But what about tires which aren't stock?

I am currently running Goodyear Wrangler Silent Armors (P265/60R18). Do these get inflated to the Ford PSI or to the PSI rating on the side-wall? Jiffy Lube, while doing their little check point list after my oil change, said that the suggested PSI for these tires is 50 PSI...does this sound right?

Thanx guys,

-Louie

 

I have always questioned the PSI ratings myself. Is Ford changing the ratings for ride quality or what? I would think that the tire manufacturer would know what pressure they designed the tire for. I'm not getting the thinking on this myself.

 

From what I have read, the PSI on the side-wall is the maximum pressure before explosion of the tire. Then again, I have no idea what is accurate. When I filled my Goodyears to the psi listed on the doorjam, they looked awfully flat. So flat in fact, that those who knew nothing about trucks or cars would comment that it looked like my tires were flat...haha.

Jiffy Lube filled them to 50psi and they look good. The ride is smooth and nothing is out of the ordinary. Yet, 50 seems awfully high to me.

 

A good way to get the correct pressure is to make a chalk line across the tread of the tire. Drive a few tire rotations and see where the chalk has came off. If it came off on the outsides, then you need to add air...if it came off in the center, you need to let out some air. Do this till you have an even wear across the chalk line. This will indicate that the tire is running level. Not center high(too much psi) or outsides high(too little psi)

 

Mine is the same way. The tires look low, like they are about to go flat. They are at the PSI Ford reccomends and it's all factory still on my truck. I guess it's normal.

 

I have always stayed close to the psi recomendations of the tire itself, paying no attention to the sticker in the truck.

 

As long as you don't go lower then ford's pressure or over the tire pressure you are ok. I run 42 psi in my 10 ply tires and adjust the pressure according to what I am doing. The closer you get to the max, the stiffer the ride and the less roll you will get from the tire. If you are towing go higher. If you want a smooth ride go to 36 psi.

 

psi pressure stated on the tire simply means one can carry the maximum load per tire specs, at this pressure. In all probability your truck will not have the "best" handling or ride, but the tires will not blow due to over flexing which produces heat, and can easily lead to tire failure.

 

That is a great method. Good idea.

 

Well now I know what I'm gonna do with the kids chalk in the garage... Just out of curiousity...when you did yours was it over the ford spec?

 

What is the original size tire on the door sticker?
50 psi on the new tires is too much - do not exceed the max cold pressure on the tire, and you only need this much pressure if you're carrying a max load.
I would use the door sticker pressures.

 

The tire pressure on the sidewall is the manufacturer's highest pressure for the largest work load. For example, if a tire is rated at 2,500lbs and lists a 45 PSI maximum tire inflation, one would not want to cross those two boundaries. It is completely feasible--although I have no idea why you would want to do this--to run maybe 55 PSI in that tire while running unloaded (assuming that the vehicle weight on that one wheel does not account for most of that 2,500lb load rating).



Spot on. This is probably the most feasible & realistic way to find that correct tire inflation level. It is offered up continuously in the four-wheeling boards...for all of those folks out there running big tires & lifts.

There are, however, a couple of things that I will add...

Start with air pressure either too high or too low. Do your chalk test, scribble notes on how it came out, lower/raise the tire pressure 2 PSI, and redo the test. What you are looking for are the transition points where the tire started exhibiting signs of over-/under-inflation. The middle point between the high & low marks is your ideal tire inflation pressure. The two schools of thought on this is to either set your cold tire pressure to that middle "optimal" number, or do a bit of additional work to find out where to set your cold tire pressure so that your tire pressure at operating temperatures is at that "optimal" pressure.

You might also consider that the ideal tire pressure will vary between the front & rear tires. So, you may want to check both tires on one side of the car/truck at the same time...beings that you are already out there with your chalk.

Lastly, if you tow or haul a particular load pretty regularly, it would be worth your time to do the same testing with that load/trailer on your truck to find that optimal tire pressure.




On a distant side note, you MIGHT be able to get your hands on a the manufacturer's load table for whatever tire you are running. This is basically a table or graph that shows what the tire inflation should be for that make, model, and size of tire given a load of X. Unfortunately, while I know they exist, I have only seen a couple of these over the years. It just seems that most manufacturer's keep them hidden away....maybe assuming it is "scientific" data that your average consumer is not interested in.