Tire Pressure for new BFG AT KO2s 285/75R16 (1 Viewer)

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I'm getting the new tires installed Saturday and wondered what pressure I should be running on highway. I saw someone in another thread using 46psi, and I know there are a couple of ways to calculate it before doing a chalk test.

Just curious what the consensus is.
 

txoutdoorx4

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We're running ours at about 40 right now and will obviously drop it once we get off-pavement.

Post up a few pics of your truck with the new tires when you get the work done. We love our BFG KO2s and can't wait to get the truck out to HIH15 this summer. :)
 

jLB

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My logic may be flawed, but I got a starting point by:

Michelin LTX AT2 285x75R16
Weight Capacity 3750 @80PSI
Curb Weight 5115

Weight Capacity x 4 = Capacity of all 4 tires

3750 x 4 = 15,000


Capacity of all 4 tires / Curb weight of vehicle = Max to actual ratio

15000 / 5115 = 2.93255132

Max PSI / Max to actual ratio = staring point PSI

80 / 2.93255132 = 27.28

So I started at 28PSI
 
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My logic may be flawed, but I got a starting point by:

Michelin LTX AT2 285x75R16
Weight Capacity 3750 @80PSI
Curb Weight 5115

Weight Capacity x 4 = Capacity of all 4 tires

3750 x 4 = 15,000


Capacity of all 4 tires / Curb weight of vehicle = Max to actual ratio

15000 / 5115 = 2.93255132

Max PSI / Max to actual ratio = staring point PSI

80 / 2.93255132 = 27.28

So I started at 28PSI

Very flawed logic. Equivalent load carrying capacity as the factory P-metric tire requires about 40 psi in a LT285/75R16:

http://toyotires.com/sites/default/files/page-files/LoadInflation_Table_P-LT_102913.pdf
 
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I don't have the KO2s, but I have KOs and have been running them at 40 psi. Seems to be a pretty good setting.
 

jLB

May be in need of a 12 step LC/LX program.
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Very flawed logic. Equivalent load carrying capacity as the factory P-metric tire requires about 40 psi in a LT285/75R16:

http://toyotires.com/sites/default/files/page-files/LoadInflation_Table_P-LT_102913.pdf


Interesting read.

But I'm not sure I found how you get 40PSI in an LT = 28-32PSI in a P

Do you have access to the full TRA tables?

The factory P-metric tires on my LX are rated at 2365lb@51PSI.
(The door card recommended pressure for these tires is 28-32PSI.)

Without the full TRA tables it still seems like guess work, chalk, adjust, chalk, adjust.......
 
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Interesting read.

But I'm not sure I found how you get 40PSI in an LT = 28-32PSI in a P

Do you have access to the full TRA tables?

The factory P-metric tires on my LX are rated at 2365lb@51PSI.
(The door card recommended pressure for these tires is 28-32PSI.)

Without the full TRA tables it still seems like guess work, chalk, adjust, chalk, adjust.......

Factory P-metric tires are only able to go to 35 PSI max (an XL goes up to 41 psi).

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=195

The factory tire load capacity is roughly 2600 lbs. P-metrics must be rated ~10% higher than LT's for SUV's/Pickups (higher center of gravity - more roll). So you subtract ~10% to find the max required rating for an LT tire which comes out to ~2350 lbs.

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=70

Look at the chart for that load and you'll see 40 psi for the 285/75R16. That much is not guess work.

Now dialing it in more precisely for your specific truck - that will require a bit more effort (chalk test, watching the wear patterns, etc).

BTW, the P-metric inflation table is on page A6 for the 275/70R16.
 

CreeperSleeper

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Or you can forget trying to come up with a formula using the stock tires since that is comparing apples to oranges.

"Tire Pressure Checker: Righting the Pressure in Your New Tires

The excitement of getting new tires can leave you giddy in the short term. But, if you expect those new tires to keep making you happy over the long haul, you’ll need to address some practical concerns before it’s too late.

Once you upgrade your tires, the first objective is identifying the correct tire pressure for street driving. To determine the ideal tire pressure for a stock truck, your best resources are the tire inflation placard and the owner’s manual. Unfortunately, these resources don’t help you when you don’t have stock or close-to-stock tires on your truck. Once you put bigger tires on your rig, it’s a whole different ballgame.

Let’s start with two simple ideas. One, the load of your truck is supported by the air volume in the tires. The constant is how many cubic feet of air can hold up a specific weight. What isn’t constant is the size of the container holding the air. Say you have two containers of different sizes holding the same volume of air. In this scenario, the smaller container will have higher pressure than the larger container. That means the larger tire needs less pressure than a smaller tire to carry the same vehicle weight. What many truck owners don’t know is how much less pressure is required. You can calculate this difference using one of four methods.

1) Let the sidewall tell you
This is the easy, guesswork method, and provides an immediate answer to your question. Find the maximum pressure as shown on your sidewall and let that be your street pressure. It will suffice until you have time to make a more accurate calculation. Note that this usually means your tire pressure will be too high, particularly if the truck is not carrying a load. This is because the maximum air pressure is the right number when the truck is fully loaded. The sidewall should also tell you the load capacity at the maximum tire pressure. That capacity can likely support half your truck’s weight, or more.

The advantage of using this maximum pressure is that it’s safe. You may even get a fuel economy benefit out of it, because your rolling resistance will be minimized.

The disadvantages are related to ride quality, handling, and uneven tread wear. At maximum pressure, you’ll feel every bump in the road. The contact patch will be concentrated in the center of the tire, which impacts the responsiveness of your steering and brakes. You may see faster tread wear in the middle of the tire.

2) Let the vehicle weight tell you
The tire maker defines the ideal tire pressure for loads of various sizes. You can get the chart for your tire from your tire maker, a tire shop, or online. A less accurate alternative would be a generic chart from the Tire and Rim Association. These recommendations are available in the most popular sizes, but the stated pressures are not specific to your tire.

Weighing your truck. The next step is to obtain the front and rear weight of your truck. Do not estimate or assume that your loaded truck weighs the same as it did when it rolled off the lot. You’ll get a more accurate result by packing your equipment onto the truck, filling the gas tanks, and even inviting some passengers to come with you to the scales.

Scales are typically available at scrap yards, recycling centers, landfills, and, of course, truck stops. You need to determine the amount of weight on your front tires, and then, separately, the amount of weight on your rear tires. If there’s a race shop near you, you may be able to use its portable scales to get these weights quickly.

At a truck stop, you’ll have to take three different weights. First, drive up and stop when only the front tires are on the scale. Record the weight. Next, drive your truck forward until all tires are on the scales. Take another reading. Lastly, drive off the scales so that only your rear tires are being weighed. If you’ve done it right, the sum of the front and rear tire readings should be roughly equal to the total truck weight. You may learn that your truck carries more weight on the front than on the rear. This isn’t that uncommon with pickups.

Next, divide the weight on your front tires by two to get the weight on each tire. Do the same with your rear tire weight.

Finally, consult your load/inflation chart again. Round the calculated weight up to the nearest tire pressure and add another 10%.

Check your results. To check your results, you can measure the tires and add pressure to balance them. Before you measure, make sure your truck is parked on flat ground. Then, along the centerline, measure the distance between the ground and the edge of the wheel on all four tires. As noted, if there are differences, add pressure to even things out. The profiles should be almost the same from front to rear.

The advantage of this method is that you should end up with the optimal pressure. Optimal means you are balancing fuel efficiency, the quality of your ride, handling and braking performance, and uniformity of tread wear.

This disadvantage of this method is that it’s tedious and could give you the wrong answer if you weigh or calculate incorrectly.

3) Let the chart tell you
If your truck has not been substantially modified, outside of the larger tires, you can use your tire inflation placard and a load inflation chart to identify a tire pressure.

The first step is to find the chart that goes with your stock tires. Locate the pressure that relates to the recommended pressure on the tire inflation placard. Then, look for the weight the tire should bear at that level of pressure. Next, get the chart for your new tires. Look for the same weight there. If that specific weight isn’t listed, select the next highest weight and record the recommended pressure.

Let’s go through an example, using a 2005 F-150HD that originally had 245/70R x 17D Load Range D tires.

According to the tire placard, at maximum load, the tire pressure should be 50 psi in the front and 60 psi in the back.
When you locate that tire at those pressures on the load inflation chart, the rated loads are 2,205 lbs. and 2,469 lbs.
The proposed new tires are 285/70R x 17D Mickey Thompson MTX Load Range D tires. The closest numbers on the load inflation chart for those tires is 2,340 lbs. and 2,540 lbs. These equate to 40 psi and 45 psi, respectively.
If you need to adjust for differences in the pressure or weight between the charts, you can do it using this formula:

Tire weight/tire pressure = Load capacity pounds per psi
You would start with the load and pressure closest to the original tire, adding or subtracting to find the proper adjusted pressure. In this example, the calculation would be:

Original tire: 2,205/50 = 44.1 pounds per psi
New tire: 2,130/35 = 60.8 pounds per psi
To determine how much tire pressure to add, subtract the weight of the new tire at pressure from the weight of the old tire at pressure. In our example, this results in 75, or 2,205 minus 2,130. Next, take that result and divide it by the pounds per psi of the new tire. This equates to 1.23, or 75 divided 60.8. Adding the 1.23 psi to our front tires would amount to 36.23 psi, which we rounded up to 37.

For the rear tires, the old tire had a slightly lower capacity than the new one. In this case, you could go with the 45 psi or let out some air to reach 43.6 psi.

4) Let the chalk tell you
You can also “calculate” your tire pressure with the chalk method. This involves coloring a section of your tire with chalk to see how much tread is making contact with the ground. Start by finding a flat road surface. Concrete is actually the best choice, but you can also do this on asphalt. Make a mark with soft chalk that goes all the way across your tread. Then, gradually drive your truck forward about 50 feet and then backwards 50 feet.

Analyze the chalk on the tire. If the chalk is only worn off on the center of the tire, reduce the tire pressure slightly and go through the process again. With the adjustment, you should see the chalk wear off more broadly. Keep making tiny adjustments in the tire pressure until the chalk wears off evenly and all the way across the tread.

You will have to complete this process for each of your four tires. Once you’ve found the right street pressure, add 10% to all four tires. Then, measure the tires and add pressure to balance them. As explained above, you need to measure from the wheel to the ground. Start by balancing the profiles of the front tires with each other. Then, balance the front tires again with the rear tires. Always adjust the tires with the smaller profiles by adding air.

The advantages and disadvantages of this method are the same as those involved in the second method above. If you go through the process correctly, you end up with the ideal tire pressure. But, this method is tedious and there’s a reasonable chance that you will make a mistake."

Taken from: http://www.4wheelparts.com/tire-wheel-package-guide/tire-pressure-checker.aspx
 

jLB

May be in need of a 12 step LC/LX program.
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Factory P-metric tires are only able to go to 35 PSI max (an XL goes up to 41 psi).


Then why would Michelin post their specs for max load @above max pressure?
MIchelin.jpg

(and yes I did mis-read the line earlier it should have been 2185lbs@44PSI)

or the long forgotten Dunlop OE tires 2403lbs@51PSI?
Dunlop.jpg
 
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Then why would Michelin post their specs for max load @above max pressure?
(and yes I did mis-read the line earlier it should have been 2185lbs@44PSI)

or the long forgotten Dunlop OE tires 2403lbs@51PSI?

Good question. Only thing I could find was this:

"Some Standard Load tires are marked with a maximum inflation pressure of 44 psi, but are still rated for their maximum load capacity at 35 psi."

http://www.tirereview.com/tire-types-and-load-capacity/

Not sure I can fully answer that one.

I've been in full on research-mode looking for tires for the LX. A lot of this stuff doesn't make sense. Not sure why a 265/75R16 requires 50 PSI, but a 285/75R16 requires 40 psi for the same load. Not sure why pretty much every LT in those two sizes is an E load.
 
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A lot of this stuff doesn't make sense. Not sure why a 265/75R16 requires 50 PSI, but a 285/75R16 requires 40 psi for the same load. Not sure why pretty much every LT in those two sizes is an E load.

The lower psi is because the larger contact patch requires less pressure to support the same load. It's why bush airplanes in Alaska with massive "tundra tires" run at low psi. A bigger tire has a contact patch that is wider and longer, therefore more square inches than a smaller tire. More square inches in each contact patch with the same number of pounds pressing down on the wheel means less psi to maintain optimal tire shape.

That's why you couldn't take r16 tires off on Honda civic and put them under a 5500lb land cruiser. The weight of the land cruiser would crush the tiny tires and mean you'd either be riding on the rims, or you'd need to crank up the psi to dangerously high levels to push the land cruiser off of the rims.

As to why load range e, I think it's because most people wanting that big a tire want the maximum durability.
 
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Thanks everyone for the answers, this is what I was hoping to get before talking to the tire guys on Saturday.
 
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The lower psi is because the larger contact patch requires less pressure to support the same load. It's why bush airplanes in Alaska with massive "tundra tires" run at low psi. A bigger tire has a contact patch that is wider and longer, therefore more square inches than a smaller tire. More square inches in each contact patch with the same number of pounds pressing down on the wheel means less psi to maintain optimal tire shape.

That's why you couldn't take r16 tires off on Honda civic and put them under a 5500lb land cruiser. The weight of the land cruiser would crush the tiny tires and mean you'd either be riding on the rims, or you'd need to crank up the psi to dangerously high levels to push the land cruiser off of the rims.

I can follow the argument, and the charts seem to support the trend.

As to why load range e, I think it's because most people wanting that big a tire want the maximum durability.

Yet, anything in a flotation size can be had in load range C...all the way up to 42"

Every thread I read about load range E, whether here or the diesel pickup forums says they aren't needed unless you're constantly hauling very heavy loads. For such an extremely small market, I don't understand the drive towards that rating...

Essentially, most of the market seems to have to choose between too light of a tire (SL) or too heavy of a tire (E).
 
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You are better off doing the chalk test. You will be suprised at how LOW you will have to run them to keep the centers from wearing out. I'm running mine at 35 to 36 PSI and rotating every 5000 miles. No abnormal wear so far with about 20,000 miles. That's with normal everyday driving on roads and with normal weight (no offroad gear).
 

hankinid

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Every thread I read about load range E, whether here or the diesel pickup forums says they aren't needed unless you're constantly hauling very heavy loads. For such an extremely small market, I don't understand the drive towards that rating...

Essentially, most of the market seems to have to choose between too light of a tire (SL) or too heavy of a tire (E).
Short version...Toyo AT's, 285-75 x 16, LR E. Unloaded...37 psi front, 40 psi rear.

For that size tire, the market (at least mine) includes a 2500 Ram pulling a trailer with 2-3 horses 90% of the time, as well as a '91 GMC suburban. Turns out, according to my tire guy, that you can get the tires in LR D, but fewer are made so the price is $15 or so more per tire...economies of scale.

On my LX, the Toyo's are have ~60K so far, tire guy and I noted tread wear / depth are perfect and tire guy estimates I should have at least another 20 to 30K left.

Link here may also help... www.4wheelparts.com/tire-wheel-package-guide/tire-pressure-checker.aspx

Steve
 
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LimaBravo,

Did you conduct your chalk test yet? Just curious what the result was.

Thanks
 
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I too have purchased 285 75 16 BFG KO2s for my OME lifted fzj 80 that can accomadate 315/ 35's. I too have spent a whole lot of money so want to get things optimal. My tire dealer was all but talked me out of them, saying we just dodnt know enough about them yet. you and I are guinea pigs. Had no snow to speak of in California, they being winter rated were a large part of my decision making. Mine are load range E (Thats said and done though In another thread I am weighing the pros and cons of load range for a much lighter truck :'88 4runner) I need to stop nerding out and go camping in one of these rigs, but the final word is not in, and I have learned a couple of things. I have been on jeep forums (shhhh!) and perused some great 4x4 mag online articles (I almost feel guilty enough to subscribe to one) I never heard of the chalk test, got pretty excited about it, but then found perhaps it is bunk. On a jeep forum a guy with some big MTZ's was hitting numbers in the 10's to get even traction, well thats excellent off road but Danger Will Robins on road.
The weight divided by tire max divided by 4 is interesting, but I think that assumes that you have the load range tire that was stock for your vehicle (another can of worms)
In one of the 4x4 mags I ran across something that made a whole lot of sense for on road tire pressure: You look at the door sticker of your rig at reccomended psi, then calculate based on that the psi for your oversize tires. I will post that.
I may gut duratracs for my 80's 4runner, and I am fortunate that the Goodyear guy is an old Pismo rat and has some good knowledge. he answerd the question: What are the best tires for sand (aside from paddles) without pause. I'll post that answer below and backwards so you dont cheat if you read my wordy post. Most of the folks at the shop see a 4wd and urge me to get the mudders. If I was a rancher in ireland cutting peat in my "Wellies", I'd probably do so.
Give me rocks ice desert or snow. not so much ice please.
A side question: just what is the best tire for slimey smooth wet cobblestones. I'd imagine super siped ice tires from Norway?
dlab serit
 
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