LT245/70/17 BFG All Terrain KO Tires

[zero204]

Hi everone,

I recently purchased a LT245/70/17 BFG All Terrain KO tires. My original tires were P245/65/17 with a 35 PSI rating. I own a 2005 ford explorer limited and was wonder what would be the approriate PSI rating for my new tires. From my understanding when changing from an P to an LT you will require a higher PSI. Right now my new tires are inflated at 35 PSI. If anyone can help me with this issue that would be great! Thanks!

 

[armysoldier30263]

im not sure about the psi rating but welcome to EF and if you would post some pics of your x with the AT tires.

 

[lynchy wa]

Gday, I found this somewhere else. Don't know if it will help.

Those tires are rated for 2469 pounds each, so they can carry FAR more than a full-loaded T*******r at maximum gross vehicle weight. Although they are a "P" rated tire, in any other size, they would be more akin to an "LT" rated tire.

What this means is that "P" rated tires usually develop their maximum traction at somewhere around 80 - 90% of the max psi as listed on the tire sidewall.

"LT" tires, on the other hand, have much stiffer sidewalls - which is why they can carry a much greater load - and get the best traction in normal (not fully loaded) driving at 70 - 80% of the max psi listed on the sidewall.

I would therefore suggest that for maximum traction, maximum tread life and maximum comfort, you start with 40 psi all around and adjust from there. You can even go down to 35 psi all around and still stay safe.

Make sure you check the pressure with an accurate gauge and check them when COLD. (The max pressure listed on the sidewall is a cold rating, and when hot, they can easily climb to 10 psi or more higher than this.)

I would not go below 35 psi with these tires, and keep in mind that if you add a heavy load or carry more than two passengers, your tires can carry this load safely if you air them up a bit. It is highly unlikely you would ever need to air them up to 50 psi because if you are carrying 10,000 pounds of gross weight, you are probably on your own here!

(A good rule of thumb is to divide your vehicle gross weight by three instead of by four to get the approximate weight range of your tires. This is because if you blow a tire on the highway, the other three must then carry the load until you get stopped and get it changed.)

It is actually a bit of a fallacy that one doesn't pay any attention to the door sticker pressures if they have swapped out the OEM tires. The door stickers are still valuable because they will tell you minimum pressures to be safe and comfortable for the average driver, almost regardless of the tires put on the truck. (There will be few, if any, tires sold today in our sizes that would not be safe at sticker pressures.) However, most of us in here are not "average" drivers, and we may seek out the optimum pressures for maximum traction at both ends, and we can play with pressures a bit to get us the best compromise pressures for our own individual needs.

For example, I rarely carry back seat passengers so I run slightly more air in the front than the rear. This keeps the fronts from tucking under in tight corners and makes for a comfortable ride. My max psi rating on the sidewall is 41 psi so I run 36 front and 32 rear.

 

[Limited02]

Open the drivers door and it will tell you what the factory air pressure should be front and rear. Mine is 30psi front and 35psi rear, but I run 35psi all around.

Edit- In regards to the door sticker, I use that as a minimum.

 

[Stic-o]

Look on the side of the tire, it will tell you what they need to be.

 

[Jager]

Look on the side of the tire, it will tell you what they need to be.

no way!

 

[lowendrider]

Numbers on the side of the tire only tell you what psi is the max and what load they will carry at that max. This doesn't mean that if a tire says 44psi max that its the best for the vehicle they're on. For example, years ago I bought a set of BFG all terrains (44psi max if i remember) to put on an 89 mazda 4x4 truck. I ran around 28-30 psi in them because thats what gave me perfect wear and even at that psi I'm sure they would have carried twice the weight of my 3200 lb truck.

 

[JM1970]

Tyre pressures.....amazing subject, difficult to perfect due to all the variables like ambient temp, road temp, vehicle load, speed, road surface, tyre brand/model, mechanical condition of steering and suspension components and on an on. But you can do some on road testing to get a pretty good pressure for your own vehicle.

The OEM recommended pressures are engineered to be the ultimate compromise, picking a relatively neutral pressure that will adequately support tyre performance over a broad range of situations. These pressures are safe but won't always be the optimum pressure for your vehicle/tyre/driving conditions.

Tyres heat up when in use....if under inflated they get too hot, over inflated they don't get hot enough. Both of these conditions adversely affect performance and wear. If you find the sweet spot you are pretty much going to be in the place for maximum performance, wear resistance and fuel economy.

A method for finding the sweet spot for your vehicle, with your particular tyres and driving conditions is the 4psi rule. Basically your pressure should rise 4psi when hot compared to it's cold starting pressure. If the rise is:

=4psi your tyre is at a good temperature;
>4psi your tyre is too hot and under inflated;
<4psi your tyre is too cool and over inflated.

To work this out you need on road testing. The beauty is that you are testing your tyres on your vehicle and seeing what they do to hopefully get a pressure that is right for you. You need a decent pressure gauge, preferably digital.

How to use the 4psi rule

1. Set your starting (cold) pressures, the OEM pressure, or your normal preferred pressures are a good place to start. For consistency you need to set the tyres to their starting pressures with your gauge when they are in a cold state.

2. Go driving for a minimum of 30 minutes, preferably 1 hour so your tyres heat up. Stop and measure where your pressures are now they are hot. If they are exactly 4psi higher, the starting pressure is correct. More than 4psi and the starting pressure is too low, less than 4psi the starting pressure was too high.

You can then use a formula to work out the required pressure adjustment where a=starting pressure and b=hot pressure. pressure adjustment=b-(a+4)x0.5

Example.......you started with 30psi front and 40 psi rear. When hot you had 37psi front and 42psi rear. Using the formula:

Your fronts increased 7psi indicating they are too hot and under-inflated. 37-(30+4)x0.5. So 37-34=3, 3 times 0.5 equals PLUS 1.5. Add 1.5psi to your front starting pressure.

Your rears increased 2 psi indicating they are not hot enough and over-inflated. 42-(40+4)x0.5 . So 42-44=minus 2, minus 2 time 0.5 equals MINUS 1. Lower your rear starting pressure by 1psi.

You now have a new reference point for starting pressures for your vehicle based on how your tyres actually performed. You need to repeat this procedure until you find the sweet starting pressure that gives you +4psi when hot.

When you change tyres run the tests again as different tyres have different temperature and performance characteristics, but this method should allow you to tune your pressures for your particular vehicle and wheel/tyre combination.

The rule can also be applied for trailers, caravans, horse floats and also works for off-road as long as you are not running something ridiculous such as 5psi.

I highly recommend using the method to establish your general everyday optimum tyre pressures. When you load up your vehicle always add a few more psi. You can check how they are going when they are hot under heavy load using the same 4psi principle.

Note that using the formula approach usually results in small adjustments to the starting pressures. You can also ballpark it a bit using the principle and not bothering with the formula......more than +4psi change raise pressure, less than 4psi change lower pressure. Trial and adjust and you will find good pressures for your vehicle based on how it's tyres are reacting to being driven.

I have used this method for years and swear by it. Have always had good results for tyre wear and performance.