so i have 33'' goodyear silent armours wrapped around 20'' Ford wheels on my '06 Fx4. i was wondering if you guys ahve any idea on what air pressure i should be running? thankshttps://www.f150online.com/forums/images/smilies/beers.gif

 

Depends upon the load range of the tire. Is it a P series, or an LT series? If an LT series, what is the load range, c, d, or e, and what is the max pressure on the tire? Without that info, no one can give you a recommendation.

 

pseries 35, load range c 40, load range d 45, load range e 50.

 

Depends upon the max. Those numbers are good if the LR C is a max of 50, the LR D is a max of 65 and the LR E is max of 80. Otherwise they are too high.

 

^^thats true, giving that he said silent armours i figured hed be around the factory size or maybe a tad larger.

 

Good rule of thumb:

P-rated tires not less than 90% of max.

C-rated tires not less than 80% of max

D-rated tires not less than 80% of max

E-rated tires not less than 75% of max

All of these suggestions are for 1/2 ton pick-ups WITHOUT a load other than the weight of the truck plus passengers.

Many people run the C, D, and E rated tires at a lot lower pressures than I've listed but once you start running lower than maxium pressures in LT tires (C, D, E tires) there load capacity diminshes exponentially, so you might as well not even have an LT tire. Especially people who are running "E" tires with 40 PSI of pressure.

 

Really you're supposed to follow your door sticker's recommendation.

 

Only if it is the same load rating as the OE. The recommended pressure for a LR C tire that comes on an F150 is 40. If he were to replace them with a P-series with a max of 35, he would be 5 psi over the max of the tire. In the reverse, if it came with a pseries that recommends 35, he would be 5lbs under pressure if he put on a LR C and even more with a higher load range.

tylerN, I looked at the Goodyear site and they only list 1 33" tire for a 20" wheel. That is an extra load P-series with a max of 44. I would not go over about 40 and under about 36 on those tires.

As far as 80% for a LR E with a max of 80, 60psi would be way overkill, even for a loaded 1/2 ton. And probably be bald in the center within 10k. I have run LR Es at 50 with excellent results, both wear and handling, with and without loads. I agree 40 is too low by far for those tires, but 60 is too high.

 

yeah i have the 33'' tires at 37.5 psi right now so that sounds good since you said to keep it between 35 and 40

 

I would make sure I was reading the tire chart at Goodyear correctly. Make sure the max pressure is 44. Also, if you had the Pirellis before, I believe they are also an extra load p-series, so you may be able to go by their recommended pressure.