BFG KO2 LT285/70R/17 Tire Pressure (once and for all)

[Renegade]

I've been using Tire Pressure Calculator (tiresize.com) to give me a better idea of the pressure I should be running in my KO2. I haven't done a chalk test yet, but I'm planning to do one to confirm. So based on that I've been running my KO2 at 39 psi. That is to achieve the same load capacity as the OEM Bridgestone Dueller that the Max Tow is equipped with from factory. I could likely run my tires lower when I'm not at capacity, either load wise or towing, hence why I need to do that chalk test. And of course I "air down" when I'm offroad, it makes a big difference comfort and traction wise.

I'm not exactly sure how that calculator is supposed to work, because it is recommending you a pressure which results in a decreased load capacity. I entered some sample values, and it gave me a 1 psi lower pressure recommendation, which results in a higher load capacity. You would need it to make a recommendation based on the same OEM load capacity in order to be more useful. As is, it seems counterproductive.

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[ShadowsPapa]

I'm not exactly sure how that calculator is supposed to work, because it is recommending you a pressure which results in a decreased load capacity. I entered some sample values, and it gave me a 1 psi lower pressure recommendation, which results in a higher load capacity. You would need it to make a recommendation based on the same OEM load capacity in order to be more useful. As is, it seems counterproductive.

I want the tires to hold up a truck weighing 5,000 pounds. That's 1250/tire - that's all each tire needs to hold up, 1/4 of the truck's weight. If I take the truck up to 6,000 pounds, then that's 1500/tire so why should I care about 2555/tire? That's 10,220 pounds.
So what's up with counting things for the max load capacity when my truck can't possibly ever weigh 5 tons.

 

[Higher_Ground]

He didn't choose P Metric in the drop down.

There's a good write up below the calculator that addresses some of the limitations and ranges it applies too.

(I still wish it had P285/75/r17 as a size... must be new or outside the specs).

From the link:

Each tire is rated with a load range, load index number, and max pressure rating. Passenger tires will be rated Light Load (LL), Standard Load (SL), or Extra Load (XL). Extra Load tires of the same size will typically have the same load capacity at the same pressure as the Standard Load tire. However, they have added load capacity above certain pressures. Light and Standard Load tires have a maximum capacity pressure rating of 35-36 psi and Extra load tires have a maximum capacity pressure rating of 41-42 psi. The maximum allowed pressure listed on a tire's sidewall can be higher however. Some tires list 44 psi and many higher speed tires will list 50-51 psi. This added pressure does nothing for load capacity. Pressures above 35-36 psi for SL tires and 41-42 psi for XL tires will not increase the load capacity of the tire. Even if you put 50 psi in an SL tire the load capacity will remain what it is at 36 psi for the higher pressure levels. Adding tire pressure above maximum load capacity is used mostly for high speed situations. A tires air pressure is increased to reduce tire deflection for the increase in rotations per second compared to typically city/highway use.

 

[Higher_Ground]

Perhaps it has something to do with dynamic loading? Or situations where one tire may not be able to support weight?

I agree that the inflation pressure recommended by the manufacturer gives you a much higher load rating than the vehicle's GVWR or GAWR would allow. However, it's been pointed out before that those are legal limits and not physical limits of what the vehicle can handle.

 

[Giljr572]

He didn't choose P Metric in the drop down.

There's a good write up below the calculator that addresses some of the limitations and ranges it applies too.

(I still wish it had P285/75/r17 as a size... must be new or outside the specs).

From the link:

I must admit that I did not, however I'm using the numbers on the door sticker, which doesn't start with a P, so I assumed that it was Metric and not P-Metric.

Also, from what I can find on the Bridgestones website, the Dueller in that size is a Metric one, not P-Metric. I could be wrong, but I think I was correct in using the metric dropdown vs the P-metric one.

 

[Giljr572]

I'm not exactly sure how that calculator is supposed to work, because it is recommending you a pressure which results in a decreased load capacity. I entered some sample values, and it gave me a 1 psi lower pressure recommendation, which results in a higher load capacity. You would need it to make a recommendation based on the same OEM load capacity in order to be more useful. As is, it seems counterproductive.

From what I understand from the text in red in the picture I've attached, the OEM Size Load capacity for the size I entered is 10% higher because it's a passenger type tire installed on a light truck. The load overage is negated when installing an LT type tire. So to match the original tires 2469 lbs @ 36 psi load capacity I need a LT type tire that as an equivalent load capacity of 2245 lbs. My KO2's load capacity is at 2273 lbs @ 39 psi, so I'm actually higher that what I needed.

 

[Renegade]

I want the tires to hold up a truck weighing 5,000 pounds. That's 1250/tire - that's all each tire needs to hold up, 1/4 of the truck's weight. If I take the truck up to 6,000 pounds, then that's 1500/tire so why should I care about 2555/tire? That's 10,220 pounds.
So what's up with counting things for the max load capacity when my truck can't possibly ever weigh 5 tons.

But what about when I'm popping wheelies? That calculator just seems to be suggesting tire pressures which are counter to the logic of needing less pressure with larger tires.

 

[ShadowsPapa]

But what about when I'm popping wheelies? That calculator just seems to be suggesting tire pressures which are counter to the logic of needing less pressure with larger tires.

Pop a wheelie in your JT and I'll bring the beer down to TN.

Yeah, the online calculators seem to be doing something rather funky with the loads or weight. If I had these tires on a full-sized truck weighing another 1,000 pounds I'd need more air in them to hold the heavier truck up with the same flat footprint on the pavement.
Lift the JT up with a jack to remove some of the weight off the tires and suddenly the tires are on the pavement in the center treads only.
When I got my truck back with these new tires they had more air in them than my smaller width original tires - about 40-41 and I could literally see the outer tread area OFF the ground. I'd have worn the centers of these new tires out that way.

 

[Renegade]

Pop a wheelie in your JT and I'll bring the beer down to TN.

Dang, now I have even more reason. Pack the cooler!

 

[smlobx]

The load bearing capacity has to be more than the static weight on each tire.

When you turn sharply at speed or break suddenly you are shifting the weight of the car either to the side or the front. This weight transfer can be considerably more than the static load on each tire…perhaps as much as 100% more.

On another note for those of us who take our vehicles off the beaten path it has been my personal philosophy to use significantly stronger tires than what came from the factory in just about every 4x4 I own. As an example in 2020 we took our F-350 srw truck with our Hallmark camper onboard from Virginia to Alaska and back. A trip of almost 15,000 miles. The truck weighed almost 11,000 pounds and the stock tire was able to carry 3750# each which should have been enough but I upgraded to a TOYO AT3 that had a capacity of 4080# each. Everyone said we would have a couple of flats due to the sharp gravel they use on the roads up there so I took a second spare but ended up never getting a flat, even running with a lower tire pressure due to the washboard roads.

 

[Higher_Ground]

I must admit that I did not, however I'm using the numbers on the door sticker, which doesn't start with a P, so I assumed that it was Metric and not P-Metric.

Also, from what I can find on the Bridgestones website, the Dueller in that size is a Metric one, not P-Metric. I could be wrong, but I think I was correct in using the metric dropdown vs the P-metric one.

My mistake, I think you were correct that they are the regular metric! Took mine off and did not remember correctly it seems.

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