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Old 12-25-2019, 05:25 AM #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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Old 01-02-2020, 05:57 PM #92
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Quote:
Originally Posted by borfoo3 View Post
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!
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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Old 04-12-2020, 01:28 PM #93
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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 previously posted Toyo table I was able to calculate the stock P-Metric load value for the 4th gen (265/65R17 - load index 110) is 2337 lbs @ 32 psi.

Correcting for the P-Metric to LT-Metric (2337/1.1) we’re left with 2125 lbs. For Toyo’s own LT295/70R17 (load index 128P - E range - 80 psi max) MT, the load 2270 lbs @ 35 psi. This seems to show you could indeed safely run the 35 psi minimum in your LTs on 4th gens (on this specific size Toyo MT). The stock 5th gen size (265/70R17) is able to carry a bit more weight (2535/1.1 = 2305 lbs) and thus would require a aa bit more pressure. This is based on Toyo’s ATs/MTs of course, but should be able to cross reference with your own brand’s load inflation tables.

Except if you’re me. The Patagonias are load index 121/118Q - the first one is for single tire usage, so I’m going with that (unless there’s someone with a 4Runner dually I don’t know about!). The problem is, Milestar doesn’t publish a load inflation table - just the load index which is 121 = 3,197 lbs (@80 psi).

Luckily the chart in the first link above happens to be for a 121 load index tire (albeit a LT285/70R17 - but the Patagonias of the same size have the exact same load index)! From that chart, ~2105 lbs is achieved at 35.2 psi. Extrapolating from that the line hits 2125 pretty much right at 35.5 psi. We can just round that up to 36 and be pretty damn close to “door jam” equivalent recommendations. 5th gen guys would use right under 40 psi (or just round up to 40) to match the stock tire ratings.

Sitting at 40 psi, as they do currently, gives me ~2315 lbs which definitely clears both the 65/70 series tires load ratings mentioned above. Also, given the 4th gen GVWR is 295 lbs less than the 5th (6300 lbs vs 6005 lbs) and my truck is usually pretty empty, I could easily get away with less than 40 psi. 36 psi or so puts me well within spec of both the factory recommendations and the tire manufacturer’s recommendations so I might give that a try next.

Sorry for the hair splitting, but it was kinda fun for me lol.
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Old 06-30-2020, 09:43 AM #94
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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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Old 06-30-2020, 12:58 PM #95
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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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Old 06-30-2020, 02:23 PM #96
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Quote:
Originally Posted by Smitty19TRD View Post
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
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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