Tire Pressure for Rock Warriors with LT285/70/17, Load range Es?

studawg

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I just put on a set of RWs with BFG AT KOs, size 285/70/17. They are Load Range Es, so max cold PSI is 80. Wondering what others are running these at. Ive got 55 in them now and am going to go drive it a bit and see how they feel.
 

gaijin

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They're going to feel like you're riding on rocks :rimshot:

The correct cold tire inflation pressure for those tires on your LC is exactly 39.3psi - anywhere from 38psi - 40psi should be fine. Same pressure Front and Rear.

Here's a graph for those visual learners in the crowd:



You're looking for about 2,286 pounds of Load Limit per tire and you achieve this between 38 - 40 psi. 55psi is WAY TOO HIGH!!!

HTH
 
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Nice graph, Gaijin. But a (potentially) dumb question: how do you choose the Load Limit of 2286? It that a Toyota spec?

I'm curious because I've got Toyo LTs and my crusier is 7000lbs (without passengers) now. I'm trying to run the lowest pressure possible tire pressure, without risking tire damage, to preserve the ride.
 

studawg

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I was actually pleasantly surprised with the soft ride at 55 PSI compared to the Coopers that were on it. I appreciate the info, but what about the recall that Toyota did for the Tundras that resulted in them recommending 46 PSI for these tires? The 200 is at least as heavy as a Tundra 4x4 CC, isn't it?
 

gaijin

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I was actually pleasantly surprised with the soft ride at 55 PSI compared to the Coopers that were on it. I appreciate the info, but what about the recall that Toyota did for the Tundras that resulted in them recommending 46 PSI for these tires? The 200 is at least as heavy as a Tundra 4x4 CC, isn't it?
You can search "Tire Pressure" for posts by me in this forum for all I've posted on the subject, but here is one of my posts that pretty much sums up the rationale for recommending 40psi F/R for LT285/70-17 tires on aa LC200:

**********************************************************

OK, but buckle up folks, it's going to be a bumpy ride ...

Without specific vehicle/tire info, all I can do is provide generalized info based on a stock 2013 LC200 running LT285/70-17 tires. It should be enough to get a feel for what may apply in your individual case.

As a base, we have the door sticker for the LC200:



The sticker gives us some important info:

- GVWR = 7,385 lbs
- GAWR Front = 3,595 lbs
- GAWR Rear = 4,300 lbs
- Tire size = P285/60R18
- Cold Tire Pressure = 33psi Front/Rear

From this info, using published Load Limit tables, we can calculate the Load Limit which results from the recommended tire size and pressure:



This calculation yields a Load Limit of 2,512 lbs (per P-Rated tire) @ 33psi.

Since we are talking about a LT-Rated tire replacing a P-Rated tire in our hypothetical, we need to calculate the required Load Limit for a LT-Rated tire. When replacing a P-Rated tire with a LT-Rated tire, the LT-Rated tire should have a Load Limit 10% less than the P-Rated tire. Therefore in our example, the LT-Rated Load Limit is calulated as follows:

P-Rated Load Limit / 1.1 (the 10% difference) = LT-Rated Load Limit
-or-
2,512 lbs per tire / 1.1 = 2,284 lbs per tire

Using this new LT-Rated Load Limit, again using published Load Limit tables, we can calculate the Cold Tire Pressure required to yield the required Load Limit. For the LT285/70-17 tires, it looks like this:



From the graph, we can see that approximately 39.3psi yields a Load Limit of 2,286 lbs which, when corrected for the P-Rated requirement = 2,515 lbs compared to the P-Rated requirement of 2,512 lbs. For simplicity, let's round up and call it 40psi.

It makes no difference whether the LT285/70-17 tire is D-Rated or E-Rated, the required pressure is the same.

**********
What we know now is:
For a stock LC200 running LT285/70-17 tires, the required Cold Tire Pressure is 40psi Front/Rear.
**********


Now, we can look at what might be appropriate for a LC200 which has additional weight added to it.

Relax, we've already slogged through the tough stuff - the rest is easy.

Examining the Load Limit graph for the LT-Rated tire above, we see the load Limits are approximately as follows at the indicated Cold Tire Pressures:

40psi = 2,315 lbs/tire -or- 9,260 lbs Total
45psi = 2,510 lbs/tire -or- 10,040 lbs Total -or- 780 lbs more than stock
50psi = 2,755 lbs/tire -or- 11,020 lbs Total -or- 1,760 lbs more than stock

So, roughly speaking:

- If you have added 780 lbs to your rig, you should be running 45psi instead of 40psi.
- If you have added 1,760 lbs to your rig, you should be running 50psi instead of 40psi.

But what if you have added a weight somewhere between the published 5psi increments?

It's not exact, but a simple calculation could be applied.

Let's say you've added 1,000 lbs to your rig.

Already you know you should be running somewhere between 45psi and 50psi. Between 45psi and 50psi, we see a difference of (11,020 lbs - 10,040 lbs = ) 980 lbs. 980 / 5 = 196 lbs per psi.

So, 1,000 lbs (desired increased capacity) - 780 lbs (added capacity @ 45psi) = 220 lbs / 196 (lbs/psi between 45psi and 50psi) = 1.12psi above 45psi = 46.12psi will yield a capacity 1,000 lbs above stock.

See? Easy, right?

*************************************************************

HTH
 
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I have stock suspension and was running 45-46psi RW BFG KO2. My problem is when i leave pavement here in WA and go over wasboard on forest roads anything over 20mph i loose traction and get passed by siennas, priuses etc... love my rav4 with old clunking suspension that flys over anything :)
Last time i decided to drop psi to 39 and the traction over washboard improved but i was still 20-25mph..
Then i drove 39psi on pavement with turns or over small bumps i felt alotof sway to the point i wished more support in the driving seat.
Quite dissaponted either with too stiff tire over the washboard or stock suspension?
Does anybody have any suggestions to improve washboard traction?
Back to 46psi on pavement. Does "rocky" heavy wheel kills suspension faster than stock? I 55k miles and just had replace lower control arm for torn bushing.. heavy wheel vs pot hole?? Again dissaponted... ok i understand its not a rally car but suppose to handle pot holes and forest roads better
 

Markuson

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Same tire/wheel combo:

38-40 on road.

25 in Ouray on trail (and on road too...just between town and trail)

Today...climbing up a serious obstacle in Moab...21.

Personally, I think running anything over 45 feels like I'm driving a flintstone car... ;)
 
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I just follow what Gaijin says... he clearly knows a lot more than I do. He writes what I just try to understand.

I actually run right at 42 on the highway. Smooth ride but firm enough to eliminate most "sway". 22-26 off road depending on the conditions.
 
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Ok clearly i didnt drop pressure low enough.. i am worried peeling the rubber of the rims in the middle of nowhere with 2 kids in the car :). I am not doing crawl but rather just want to get to hiking trails going 30-50mph. So what kind of driving is safe with 21psi? 25psi? Thank you
 
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It depends on how far you have to drive at 30-50. If it's a couple of miles, I wouldn't bother airing down at all. If it's longer, then my choice would be to air down to around 30 for that kind of driving. Air down more if you are crawling, and the tougher the terrain, the more I air down to increase traction and driving comfort.
 

studawg

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According to this document which tells you everything you could want to know about 17" TRD RW fitment on Tundras, Sequoias and LCs, Toyota recommends 46 PSI in LT285/70/17s on a LC.... LINK
 

studawg

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Here's a picture of the label that they put on Sequoias and Tundras fitted with RWs and LT285/70/17s as a result of the recall....The sticker for the LC is a different part number because the spare tire size is different, but the Toyota PSI recommendation for the LT285/70/17 tire on a LC200 is the same, 46 PSI all around, confirmed by another Mud member with the sticker.

tire label.png
 

gaijin

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Here's a picture of the label that they put on Sequoias and Tundras fitted with RWs and LT285/70/17s as a result of the recall....The sticker for the LC is a different part number because the spare tire size is different, but the Toyota PSI recommendation for the LT285/70/17 tire on a LC200 is the same, 46 PSI all around, confirmed by another Mud member with the sticker.
I'm well aware of that tire pressure recommendation and those stickers which show 46psi (I have one, but there is no sticker available for the Land Cruiser which shows the correct spare tire size). That doesn't change the fact that 46psi is an incorrect recommendation.

Bear with me, there will be some more math ...

First, please remember that the OEM tires are P-rated tires: P285/60-18 @ 33psi = 2,512 pounds Load Limit.

The Air Pressure / Load Limit chart for the LT 285/70-17 tires does not change (see above) - it is an industry standard table.

If you follow the chart for the LT285/70-17 tires to achieve the same Load Limit value as the OEM tires you will find ... drum roll please ... just about 46psi.

The problem is that 2,512 pounds for a P-Rated tire is not the same as 2,512 pounds for an LT-Rated tire.

In a simple world, P-Rated tires would be replaced with P-Rated tires and LT-Rated tires would be replaced with LT-Rated tires. In our world, however, we are replacing P-Rated tires with LT-Rated tires. Due to the differences in construction and load carrying abilities between P-Rated tires and LT-Rated tires, a "translation factor" must be applied to the Load Limit values. The good news is, this factor is a simple 10%.

When P-Rated tires are fitted to an LT-Rated application, the Load Limit value of the P-Rated tire must be reduced by 10%.

Conversely, when LT-Rated tires are fitted to a P-Rated application, the Load Limit value of the LT-Rated tire must be increased by 10%.

So ...

In our case, what we know is the Toyota recommended Load Limit for the OEM P-Rated 285/60-18 tires @ 33psi is 2,512 pounds. This is based on the information on the door sticker that comes with every truck.

What we are doing with the RW wheels and LT-Rated 285/70-17 tires, is fitting an LT-Rated tire to a P-Rated application.

This requires we INCREASE the Load Limit value on the Load Limit chart for the LT-Rated tire if we want to find an equivalent air pressure to the P-Rated OEM application.

IN our case, this is 2,286 pounds @ 39.3psi increased by 10% = 2286 x 1.1 = 2514.6 pounds which is close to the 2512 pounds recommended by Toyota for the OEM P-rated tire.

Bottom line:

33psi for OEM P285/60-18 tires

Has the same load carrying capacity as

39.3psi for LT285/70-17 tires.

If you want to research further into what, exactly, "industry standards" are and how they should be applied to cases just like this, anyone can purchase and refer to the relevant publications here: The Tire and Rim Association, Inc.

HTH
 

studawg

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I'm well aware of that tire pressure recommendation and those stickers which show 46psi (I have one, but there is no sticker available for the Land Cruiser which shows the correct spare tire size). That doesn't change the fact that 46psi is an incorrect recommendation.
There is, in fact, a unique sticker for the LC200, stating the spare tire size as P285/60/18. This was confirmed to me by a member on this board that ordered the sticker and put it on his LC. The part number for that sticker is in the picture above. So you are saying Toyotas engineers did the math wrong?
 
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I have couple questions:
What kind of accident happened with tundra to promt a recall and was a specific psi involved?
If we take tundra gwr into account with recomended psi should it be 46 or 40 for lc?
 

studawg

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Pics of VIN sticker from a 2008 LC and a 2010 Tundra Crew Cab 4x4 Rock Warrior edition.

GVWR for the LC is higher than that of the Tundra....


IMG_0001_2.jpg

IMG_0002_2.jpg


That Tundra had obviously not had the new sticker put on yet, indicating PSI recommendation of 46.
 
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Seems counterintuitive that the lighter construction P-rated tire requires LESS pressure than the heavier LT tire for the same load.

What gives?
 

studawg

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I have couple questions:
What kind of accident happened with tundra to promt a recall and was a specific psi involved?
If we take tundra gwr into account with recomended psi should it be 46 or 40 for lc?
It was actually a "voluntary non-compliance campaign". The TPMS in the vehicle was set for the P rated tires at the factory, but the RWs and LT tires were added at the port or the dealer, and when that was done the TPMS wasnt recalibrated for the added pressure.


http://www-odi.nhtsa.dot.gov/acms/cs/jaxrs/download/doc/ACM17089364/RCMN-11V148-1188.pdf
 
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