12-25-2019, 05:25 AM
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#91
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I've been running my LT KO2s for a while at 35 psi, and always felt like it was under-inflated.
So after inflating my tires yesterday I went through a quick calculation to see what number makes sense.
The goal is to see, given the same load per tire, at what LT tire pressure we get the same as stock P-rated tire pressure? Here's how it went:
Stock 4runner suggested tire pressure is 32psi
Bridgestone A/T Revo (P 265/70 r17)
load @ max pressure = 2535lbs @ 44psi
My tires: BFG KO2 (LT 275/70/r17)
load @ max pressure = 3195lbs @ 80psi
going by per tire load @32psi = (32/44)* 2535 = ~1844 lbs per tire (meaning at 32 psi the stock tires can each carry this load)
to get the same above per tire load on the LT: (1844/3195)*80 = ~46 psi
The above assumes a linear relationship between tire pressure and tire load capacity, which may not be 100% true.
However, this tells us that the LT tire needs ~46psi to provide the same load rating per tire as the P-rated stock tire. Again, not 100% accurate, but to me seems like a good start point.
Ride will suffer (LT tires are stiffer) but may helps some mpgs. Plus they finally 'look' right!
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Borfoo3's '15 TEP-KDSS 'no longer' mild build
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01-02-2020, 05:57 PM
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#92
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Join Date: Sep 2018
Location: Denver, CO
Posts: 220
Real Name: Carlo
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Quote:
Originally Posted by borfoo3
I've been running my LT KO2s for a while at 35 psi, and always felt like it was under-inflated.
So after inflating my tires yesterday I went through a quick calculation to see what number makes sense.
The goal is to see, given the same load per tire, at what LT tire pressure we get the same as stock P-rated tire pressure? Here's how it went:
Stock 4runner suggested tire pressure is 32psi
Bridgestone A/T Revo (P 265/70 r17)
load @ max pressure = 2535lbs @ 44psi
My tires: BFG KO2 (LT 275/70/r17)
load @ max pressure = 3195lbs @ 80psi
going by per tire load @32psi = (32/44)* 2535 = ~1844 lbs per tire (meaning at 32 psi the stock tires can each carry this load)
to get the same above per tire load on the LT: (1844/3195)*80 = ~46 psi
The above assumes a linear relationship between tire pressure and tire load capacity, which may not be 100% true.
However, this tells us that the LT tire needs ~46psi to provide the same load rating per tire as the P-rated stock tire. Again, not 100% accurate, but to me seems like a good start point.
Ride will suffer (LT tires are stiffer) but may helps some mpgs. Plus they finally 'look' right!
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Nice reasoning, makes sense to me.
I got the 265 in C rating and after a few tests I ended up deciding running it at 38-40psi, which sits in between the stock 32psi and your range E 46psi, so I guess it was a good guess lol
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04-12-2020, 01:28 PM
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#93
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Join Date: Nov 2014
Location: Austin, TX
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I recently moved to LT295/70R17 Patagonia MT (E) and was doing a little research on what the appropriate tire pressures should be. Discount Tire filled them to the door jam specs (bad) so I've been giving 40 psi a go driving around today but I decided to dig a bit deeper.
Using the calculations here and cross referencing the data from the Toyota load inflation tables I was able to calculate the stock P-Metric load value for the 4th gen (265/65R17 - load index 110) is 2260 lbs @ 32 psi.
Correcting for the P-Metric to LT-Metric (2250/1.1) we're left with 2055 lbs. The Patagonias are load index 121Q which hold 2215 lbs. @35 psi. This seems to show you could indeed safely run the 35 psi minimum in your LTs on 4th gens (which is the actually the minimum recommended on this size). The stock 5th gen size (265/70R17) is able to carry a bit more weight (2425/1.1 = 2205 lbs) but since 35 psi still satisfies this requirement (2215 lbs), it's the same.
35 psi puts me well within spec of both the factory recommendations and the tire manufacturer's recommendations so I'm moving to that.
Sorry for the hair splitting, but it was kinda fun for me lol.
Edit: Tire Pressure Calculator - this seems to be very accurate and based on industry load inflation tables. Interestingly enough the LT high flotation in sizes we might run can be run as low as 25psi (vs LT Metric tires that start at 35 psi). Something I'm now researching since I'm moving to 35s...
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Last edited by Drift Monkey; 10-12-2020 at 06:01 AM.
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06-30-2020, 09:43 AM
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#94
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Junior Member
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Join Date: Apr 2020
Location: Salt Lake City
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Real Name: Matt
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Long time lurker first time poster. I came across this thread while looking for cheap mods for the 4th gen. I decided I would chime in and give my .02 cents. I use the chalk method when I change model or size of tire. This has been the best way for me to make sure the tires are properly inflated. It's kind of a pain in the butt because you need the tires to be cold and you need a flat level spot to roll forward a couple of revolutions.
I recently discovered a calculator for get the pressure correct and I have tested it out on my Tundra, my GF's 4th Gen 4R, my buddies Tacoma and another buddies FJ Cruiser. We did the chalk method with all of the mentioned rigs and when I put the information in the online calculator I came up with the same PSI as I did with the chalk method. There are other useful tools on this website like gearing and speedo calculations as well as more. Check it out when you have a minute, I have found it very useful.
Tire Pressure Calculator
Last edited by MDobb79; 06-30-2020 at 09:45 AM.
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06-30-2020, 12:58 PM
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#95
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Join Date: Mar 2019
Location: North Florida
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This tool was within 1 PSI of what I had hand calculated for my tire change. Very nice.
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06-30-2020, 02:23 PM
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#96
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Junior Member
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Quote:
Originally Posted by Smitty19TRD
This tool was within 1 PSI of what I had hand calculated for my tire change. Very nice.
Sent from my moto g power using Tapatalk
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As I already mentioned for me the chalk method has always been the most accurate way to ensure proper tire contact. I feel confident in using the calculator from now on instead of the chalk. They also have a wheel offset calculator that is pretty cool and gives a nice visual.
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07-29-2020, 10:34 AM
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#97
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Join Date: Jul 2020
Location: Los Angeles, CA
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Solid break down! I was wondering what LT meant, thank you.
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07-29-2020, 11:49 AM
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#98
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Join Date: Mar 2010
Location: denver
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Quote:
Originally Posted by DontDrinknDerive
Solid break down! I was wondering what LT meant, thank you.
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light truck.
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12-12-2020, 11:50 AM
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#99
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Join Date: Jul 2018
Location: Canada, eh?
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Real Name: Jim
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I’ve read this thread, and several others on the topic, and it seems to me there may be 2 different conversations happening. Hear me out...
One line of thinking is trying to determine the correct tire pressure based on load capacity. Either by converting from P to LT or working from the load characteristics of the LT and factoring in GVWR. This seems to land around 43-44psi. Higher if you are maxing out on vehicle weight.
The other line of thinking is trying to optimize road contact, either by chalking or heat measurements (or whatever). This seems to come in lower than the previous method, somewhere in the mid to high 30s.
If you’re towing, or otherwise heavily loaded, and need to ensure the tires can handle the weight, the first approach makes perfect sense...the tires need to be able to support the weight. But...for the majority of us (or the majority of the time) when it’s just a stock(ish) 4Runner and 1 or 2 people, doesn’t the 2nd approach make more sense? My runner is a bone stock 2020 with 265 K02s, and with the tires at 38psi, on a cool/cold day with wetish roads, there is a very noticeable lack of traction. The same pressure on a warm/hot day (yes, tires adjusted as temp changes) and the traction seems fine. So I have dropped the pressure to 34 to try that out, and it seems to be much improved.
Does this thinking make sense, or do you think 34 is just too low for an LT on this rig?
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12-12-2020, 12:05 PM
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#100
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Join Date: Aug 2010
Location: Mississauga, ON
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Quote:
Originally Posted by jimgsmith
I’ve read this thread, and several others on the topic, and it seems to me there may be 2 different conversations happening. Hear me out...
One line of thinking is trying to determine the correct tire pressure based on load capacity. Either by converting from P to LT or working from the load characteristics of the LT and factoring in GVWR. This seems to land around 43-44psi. Higher if you are maxing out on vehicle weight.
The other line of thinking is trying to optimize road contact, either by chalking or heat measurements (or whatever). This seems to come in lower than the previous method, somewhere in the mid to high 30s.
If you’re towing, or otherwise heavily loaded, and need to ensure the tires can handle the weight, the first approach makes perfect sense...the tires need to be able to support the weight. But...for the majority of us (or the majority of the time) when it’s just a stock(ish) 4Runner and 1 or 2 people, doesn’t the 2nd approach make more sense? My runner is a bone stock 2020 with 265 K02s, and with the tires at 38psi, on a cool/cold day with wetish roads, there is a very noticeable lack of traction. The same pressure on a warm/hot day (yes, tires adjusted as temp changes) and the traction seems fine. So I have dropped the pressure to 34 to try that out, and it seems to be much improved.
Does this thinking make sense, or do you think 34 is just too low for an LT on this rig?
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There's is 3rd line of thinking - chose LT tire inflation using Toyota 4runner manual which is says:
"Maximum load of tire
Check that the number given by dividing the maximum load by 1.10 of
the replacement tire is greater than 1/2 of the Gross Axle Weight Ratings
(GAWR) of either the front axle or the rear axle, whichever is greater."
If you use this line of thinking - the minimum tire pressure for C load stock size tire should be not less than 35 psi when you have your truck fully loaded..
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Goodyear Wrangler Duratracs
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12-12-2020, 02:48 PM
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#101
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Member
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Join Date: Jul 2018
Location: Canada, eh?
Posts: 37
Real Name: Jim
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Join Date: Jul 2018
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Quote:
Originally Posted by scanny
There's is 3rd line of thinking - chose LT tire inflation using Toyota 4runner manual which is says:
"Maximum load of tire
Check that the number given by dividing the maximum load by 1.10 of
the replacement tire is greater than 1/2 of the Gross Axle Weight Ratings
(GAWR) of either the front axle or the rear axle, whichever is greater."
If you use this line of thinking - the minimum tire pressure for C load stock size tire should be not less than 35 psi when you have your truck fully loaded..
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So 35 psi fully loaded means what when not fully loaded? Seems like 34 might be ok?
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12-12-2020, 10:14 PM
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#102
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Join Date: Aug 2010
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Quote:
Originally Posted by jimgsmith
So 35 psi fully loaded means what when not fully loaded? Seems like 34 might be ok?
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I think so - yes, but as far as I remember those load vs. pressure graphs they are not linear, so 32 psi might be probably dangerous. Also it depends on speed and ambient temperature. For example if you driving on trails with walking speed you can go to 20 psi and you will be fine. But on highway your tire likely to overheat and blow up. So if I drive empty truck and have 34 psi on LT C load tires I wouldn't probably be too much concerned, but I prefer to keep tires at 36-38psi since for every 10 degrees of temperature drop, tires will drop 1-2 psi.
And with our weather we can have 10 degrees difference between early morning and noon on some days. That's my theory too, what I know for sure is that for past 9 years I have C load Duratracs I didn't have any issues running them at 36-38psi.
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12-13-2020, 11:45 AM
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#103
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Join Date: Jul 2018
Location: Canada, eh?
Posts: 37
Real Name: Jim
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Join Date: Jul 2018
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Quote:
Originally Posted by scanny
I think so - yes, but as far as I remember those load vs. pressure graphs they are not linear, so 32 psi might be probably dangerous. Also it depends on speed and ambient temperature. For example if you driving on trails with walking speed you can go to 20 psi and you will be fine. But on highway your tire likely to overheat and blow up. So if I drive empty truck and have 34 psi on LT C load tires I wouldn't probably be too much concerned, but I prefer to keep tires at 36-38psi since for every 10 degrees of temperature drop, tires will drop 1-2 psi.
And with our weather we can have 10 degrees difference between early morning and noon on some days. That's my theory too, what I know for sure is that for past 9 years I have C load Duratracs I didn't have any issues running them at 36-38psi.
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Thanks. Whenever I take it to Toyota for service they drop the pressure back to 32 to match what’s on the door. I would have thought they would understand the different type of tire but I guess not.
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12-13-2020, 12:13 PM
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#104
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Join Date: Aug 2010
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Quote:
Originally Posted by jimgsmith
Thanks. Whenever I take it to Toyota for service they drop the pressure back to 32 to match what’s on the door. I would have thought they would understand the different type of tire but I guess not.
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I found that not only Toyota dealership but also Goodyear tire dealers don't have good understanding of LT tires loading tables. I normally just tell them don't change tire pressure but still check it when get home after oil change : )
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02-16-2021, 08:35 PM
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#105
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This has been an education!
My 2020 Off Road Premium has the stock Bridgestone Dueler H/T tires-684II. Size is P265/70/17. When I looked at the TPMS system, they were set at 55 psi! Double-checked and sure enough, 55. I dropped them to 38 psi. We'll see how it drives.
From what I gathered in reading this thread, the "P" in the "P265" is what makes it a P-metric tire? If it was a LT tire, it would be LT265?
Thanks to all for the (overwhelming) information!
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