35's and AHC ... too bouncy now?

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gaijin said:
Technical data:
The Load/Inflation tables published by TRA (Tire & Rim Association) show the allowable range of tire pressures. LT-Metric tires are limited at the low end at 35psi.
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It doesn't show "allowable range." It shows "minimum pressure" to support a given load.
 
hoser said:
It doesn't show "allowable range." It shows "minimum pressure" to support a given load.
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Do you see anything below 35psi? That means that there is no "minimum pressure" below the minimum of 35psi on the chart. Which, in turn, means there is no "given load" which can be supported below 35psi. Which means there is no allowable pressure below 35psi that will satisfy design criteria. How else can I state it?

Let me try to explain by example.

I know the Load/Inflation tables published by TRA (the folks that set the tire standards) show the design tire Load Limits at given pressures. All tires have to meet these design loads.

This means that for ALL tires of a given design and size must meet the same design load standards.

For ALL LT325/60R18 tires, for example, no matter the manufacturer, the tire must support a Load Limit of 2,535 lbs at 35psi.

Using the tables (as I posted above) what would the Load Limit be at 40psi?

1773449010780.webp


Correct! 2,715 lbs.

OK, so you want to run 30psi, what would the specified Load Limit be at 30psi? Not in the table? Right, because it is not approved.

Not approved means not allowed.

HTH
 
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Thanks Gents! Lot of good feedback.

More data ... I've reached out to Falken asking their minimum and they declined to give a specific number implying they don't have one. Just good common sense, tho, tells me I'd like to be in a 35-40 range for safety, especially since I'm a max velocity everywhere (thank you Harrop). I think I will "play" with pressures and see what that gets me. I've already gone from 36-32'ish. No noticeable change or effect. I'll continue playing but the goal would be settle at something plush for ride that's at or above 35psi.

Perry Parts is looking up my old order and investigating if he can help. He's already offered to cover me with an exchance and work on this as fast as he can. And I just have to take a second here and say he's super solid. Also, what a community here on Mud as I met Perry many years ago on here.

My hope is playing with the bump stops, PSI, and sways reverting back to OEM is enough. Then I can tinker with the AHC for the fine tune.

I'll update the thread later.

Thanks for the inputs.
 
lx4dp said:
I’m considering lowering the AHC height (reversing the sensor lift) by ~0.5–1.0" to see if that helps.
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Spend 10 minutes to do this first. It's about the quickest thing you can do and it'll answer many things.

Again, it's not the tires. You have tried easonable pressures where it should ride nicely.
 
gaijin said:
Do you see anything below 35psi? That means that there is no "minimum pressure" below the minimum of 35psi on the chart. Which, in turn, means there is no "given load" which can be supported below 35psi. Which means there is no allowable pressure below 35psi that will satisfy design criteria. How else can I state it?

Let me try to explain by example.

I know the Load/Inflation tables published by TRA (the folks that set the tire standards) show the design tire Load Limits at given pressures. All tires have to meet these design loads.

This means that for ALL tires of a given design and size must meet the same design load standards.
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The primary purpose of the Tire and Rim Association was to standardize different manufacturer specifications, so the consumer could properly choose tires for their vehicle.... from any manufacturer. LT-Metric tires span from load range C to load F.... and in various speed ratings. They are not all going to blow up at 34psi at the same time. How could you even design that? The TRA only makes the lower requirement at 35psi. If 35psi was the absolute lowest psi limit, don't you think manufacturers would state so on the sidewall?

Now, LT-Floatation have a different target market. They run typically wider tires and want floatation and hence run lower pressure. Take a look at the TRA tables and the minimum pressure on the LT-Floatation tables is 25psi.... not because it is the minimum but because that is what people typically run.

Now, for personal experience... I have run many LT-Metric tires for tens of thousands of miles under 35 psi without issue... under different vehicles and even trailers. No tread separation, no overheating, no problem.

@lx4dp Inquired about lowest pressure and they didn't have an answer. They don't need to have answer because nobody requires it.
 
Looks like PerryParts found out I ordered the wrong bump for the LX. At one point he and I talked about a build and pulling out the AHC so he didn't flag it but now that I'm having issues it's all adding up. He's offered to exchange parts for me. (he's an awesome vendor for those interested).

Hope this solves a majority of the issues. I'll still play with sways, tire PSI, and AHC settings. More to come. Thanks gents.
 
hoser said:
The primary purpose of the Tire and Rim Association was to standardize different manufacturer specifications, so the consumer could properly choose tires for their vehicle.... from any manufacturer. LT-Metric tires span from load range C to load F.... and in various speed ratings. They are not all going to blow up at 34psi at the same time. How could you even design that? The TRA only makes the lower requirement at 35psi. If 35psi was the absolute lowest psi limit, don't you think manufacturers would state so on the sidewall?

Now, LT-Floatation have a different target market. They run typically wider tires and want floatation and hence run lower pressure. Take a look at the TRA tables and the minimum pressure on the LT-Floatation tables is 25psi.... not because it is the minimum but because that is what people typically run.

Now, for personal experience... I have run many LT-Metric tires for tens of thousands of miles under 35 psi without issue... under different vehicles and even trailers. No tread separation, no overheating, no problem.

@lx4dp Inquired about lowest pressure and they didn't have an answer. They don't need to have answer because nobody requires it.
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For your edification:

studawg said:
Absolutely, Im just one of those people that has to get to the bottom of things. If Toyota and BFG are wrong about something like this, I want to know it. Considering that this would have happened after the Ford/Firestone fiasco and that Toyota has also had its fair share of recent recalls, I just find it hard to believe they got this wrong. I don't think the cost of those incidents to the manufacturers can even be calculated, certainly not the damage to their image.


To your questions,

1. This is the original Toyota document about the TRD wheels, stating 40 PSI for the tires and stating the original part number for the LC sticker. This is the Campaign/Recall documentation stating the old part number for the LC sticker and the new part number for the LC, which says 46 psi. Note section 6. This is what has me stumped. Why the change?

2. I think you first said Land Cruiser and not LC200 because I went and checked my TIP on the FJ62 and it is 29 front, 42 rear. I guess BFG is going by the differences in GAWR front to rear.

3. I was mistaken; was confusing registering new TPMS sensors, which has to be done with TEchstream, with initializing the system for new pressures, which is simply done with the reset button.

4. It is my contention that 33 Psi in the stock tire does NOT equal 40 Psi in the LT tire in our application, so that renders that point moot. It is my contention that there are other factors involved, i.e. wheel size, wheel width, spring rates of the tires themselves and its effect on overall suspension, etc... that are combined to produce the ideal PSI. The conversion calculation just provides a minimum pressure at which to start. But I could be wrong of course, I just want to know it and figure it all out.

One other tidbit I learned, as of the 2014 MY, Toyota does NOT put a recommended PSI on the TIP (Tire Info Placard) on the doorjamb on the LC! Just GVWR, GAWR and tire size. Whats the deal there?
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OK! You have provided some very helpful links - which I actually followed, read and dug a little deeper - that have, I think, provided answers that we can both agree on.

Bear with me, I'll try to keep it short and to the point.

- The campaign/recall doc you cited explains that, basically, Toyota would be conducting a voluntary non-compliance action because the TPMS system, as then currently installed, would not trigger in compliance with Federal Motor Vehicle Safety Standard No.138 (find it here: TPMS FMVSS No. 138, Introduction )

- In FVMSS No. 138 it states that the minimum trigger pressure for LT Load Range E tires must be >35psi. This would require a recommended cold tire inflation pressure of 46psi in order to meet the 25% part of the same regulation. Here is the pertinent excerpt from that regulation:


  • The rationales for the minimum activation pressure are:

    A 20 psi floor for p-metric tires is required because the agency believes that below that level, safety in terms of vehicle handling, stability performance, and tire failure is an issue. The agency ran a variety of p-metric tires in what it calls a "low pressure endurance test" at 20 psi with a 100 percent load at 75 mph for 90 minutes on a dynamometer. None of these tires failed. In a second set of test it calls a "low pressure high speed test" at 20 psi with a 67 percent load for 90 minutes, in 30 minutes steps at 140, 150, and 160 km/h (87, 93, and 99 mph), about 30 percent of the tires failed. Since tires could pass the "low pressure high speed test" at 20 psi, this leads the agency to believe that there will be a safety margin, in terms of tire failures, if a TPMS warning is provided at or above 20 psi, that will allow consumers to fill their tires back up before the tire fails, unless the vehicle is driven at very high speeds (above 140 km/h or 87 mph).

    The lowest inflation pressure used in the 2000 Tire & Rim Association Yearbook is 140 kPa (20 psi) for P-metric tires. In the 2001 Tire & Rim Association Yearbook, the 140-kPa pressures have been deleted, apparently because the Association believes they are too low for P-metric tires. The agency agrees that 140 kPa is too low and believes a floor is needed to assure that drivers are warned when tire pressure gets to or below that level. For the LT tires, we used the 2000 JATMA yearbook for the lower limits for Load Range C, D, and E tires. For most cases, the floor is about 58 percent of the maximum inflation pressure.
- So, basically, here's what apparently happened:

1. Toyota originally recommended the correct inflation pressure of 40psi for the LT285/70-17 tires.

2. Toyota became aware that when the TPMS system triggered at 30psi (40psi - 25%) for those tires, it was below the threshold stipulated by FVMSS no.138.

3. In order to avoid being found in non-compliance with a Federal Motor Vehicle Safety Standard, Toyota raised the recommended inflation pressure for the LT285/70-17 tires from 40psi to 46psi so the TPMS would trigger at 35psi (46 - 25%) and be in compliance.

What does this action by Toyota leave us with?

- A TPMS system that is in compliance with FMVSS No.138.
- A recommended tire inflation pressure that is 6psi higher than Toyota would otherwise recommend.

Miscellaneous observations/conclusions:

- I have been using information from the 2014 Tire & Rim Association Yearbook which is, apparently, 14 years more recent than the 2000 Tire & Rim Association Yearbook cited in the federal regulation.

- The threshold low pressure of 35psi for Load Range E LT tires seems rather broad and arbitrary. This has been chosen to cover the worst case scenario of the TPMS triggering at 58% of Max Load which is far more than any of us with our LC200's will ever approach.

- I don't have TPMS sensors in my RW wheels, so all this TPMS talk is outside of my use case. This means that even if Toyota is forced to recommend a tire pressure 6psi higher than they would prefer just to comply with a TPMS federal regulation, I do not have to follow it to be safe.

Now to directly address your points:

1. Very helpful reference information. I think I have provided my take on, "Why the change."

2. Since we are in the 200 Forum, my statement was originally and still is for "LC200." I don't know what BFG was going by, but Toyota still recommends 33psi Front/Rear for the OEM P285/60-18 tires despite the different GAWR's of 3595LB Front / 4300LB Rear.

3. Hey, we all make mistakes.;)

4. I think that I have established that 33psi for the OEM P285/60-18 tires is equivalent to 40psi for the LT285/70-17 tires in our application. Toyota changed the recommended pressure from 40psi to 46psi in order to be in compliance with a threshold trigger pressure for ALL LT tires in general - nothing specific to our application.

studawg said:
One other tidbit I learned, as of the 2014 MY, Toyota does NOT put a recommended PSI on the TIP (Tire Info Placard) on the doorjamb on the LC! Just GVWR, GAWR and tire size. Whats the deal there?
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Unless the law has changed (see it here: Tire Safety Information, Final Rule. ) there has to be a label somewhere showing recommended tire pressures:


    • 3. Vehicle Labeling
    Labeling requirements are also contained in 49 CFR part 567, Certification, 49 CFR part 575, Consumer Information Regulations, FMVSS No. 110, Tire Selection and Rims, applicable to passenger cars and to non-pneumatic spare tire assemblies for use on passenger cars, and FMVSS No. 120, Tire Selection and Rims for Motor Vehicles Other Than Passenger Cars.�

    Section 567.4 requires vehicle manufacturers to affix to each vehicle a label bearing, among other things, the Gross Vehicle Weight Rating (GVWR), which must not be less than the sum of the unloaded vehicle weight, rated cargo load, and 150 pounds times the vehicles rated seating capacity; and the Gross Axle Weight Rating (GAWR), which is the value specified by the manufacturer as the load carrying capacity of a single axle system.

    Paragraph S4.3 of FMVSS No. 110 requires manufacturers to affix a placard to each passenger car's glove compartment door or an equally accessible location showing the vehicle's capacity weight, designated seating capacity, the manufacturer's recommended cold tire inflation pressure for maximum loaded vehicle weight, the manufacturer's recommended tire size designation, and, for a vehicle equipped with a non-pneumatic spare tire assembly, the non-pneumatic identification code required by FMVSS No. 129, New Non-Pneumatic Tires for Passenger Cars.�The required information is intended to promote the vehicle's safe performance by preventing the overloading of the tires or the vehicle itself.

    FMVSS No. 120 requires that each vehicle show, on the label required by 567.4, or on a tire information label (S5.3.2(b)), the recommended tire size designation appropriate for the GAWR, the size and type designation of rims appropriate for those tires, and the recommended cold inflation pressure for those tires such that the sum of the load ratings of the tires on each axle (when the tires load carrying capacity at the specified pressure is reduced by dividing 1.10, in the case of a tire subject to FMVSS No. 109, i.e., a passenger car tire) is appropriate for the GAWR.
Final thoughts:

It's always good to find out why things are the way they are. As an engineer, I tend toward the scientific approach; but it is clear that when dealing with motor vehicles, there are always regulatory and marketing considerations that can potentially muddy the waters.

I'm still very confident in recommending 40psi for the LT285/70-17 tires, but fully expect others to make their own decision based on the facts as best they can determine them, and whatever makes them comfortable - no harm, no foul.

HTH

ETA: Here is an updated link to FVMSS No. 138: FMVSS-No138
 
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gaijin said:
The lowest inflation pressure used in the 2000 Tire & Rim Association Yearbook is 140 kPa (20 psi) for P-metric tires. In the 2001 Tire & Rim Association Yearbook, the 140-kPa pressures have been deleted, apparently because the Association believes they are too low for P-metric tires. The agency agrees that 140 kPa is too low and believes a floor is needed to assure that drivers are warned when tire pressure gets to or below that level. For the LT tires, we used the 2000 JATMA yearbook for the lower limits for Load Range C, D, and E tires. For most cases, the floor is about 58 percent of the maximum inflation pressure.
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Firstly, just wanted to point out you are basing your argument on a year 2000 JATMA publication in which a study was done, who knows, 5,10 years before that. We are talking 25-35 years ago. A lot of technological advances in tires since then. But I'll go with it.

"For the LT tires, we used the 2000 JATMA yearbook for the lower limits for Load Range C, D, and E tires. For most cases, the floor is about 58 percent of the maximum inflation pressure."

Okay, I choose LT-Metric tire LT365/75R16 for my FJ Cruiser. It meets minimum load rating. It is a Load C tire with a maximum pressure of 35psi. According to your 25 year old reference, the lower limit is 58%. Fifty-eight percent of 35psi is 20 psi. According to your Rock Warrior document, I should set my pressure to 27psi because 27 with a 25% loss is 20 psi and my TPMS will alert me in time from having a blowout.

The "correct" pressure is certainly lower than 35psi but it's not shown on the table. 35 psi is NOT the minimum pressure for all LT-Metric tires.

load.webp
 
hoser said:
Firstly, just wanted to point out you are basing your argument on a year 2000 JATMA publication in which a study was done, who knows, 5,10 years before that. We are talking 25-35 years ago. A lot of technological advances in tires since then. But I'll go with it.

"For the LT tires, we used the 2000 JATMA yearbook for the lower limits for Load Range C, D, and E tires. For most cases, the floor is about 58 percent of the maximum inflation pressure."

Okay, I choose LT-Metric tire LT365/75R16 for my FJ Cruiser. It meets minimum load rating. It is a Load C tire with a maximum pressure of 35psi. According to your 25 year old reference, the lower limit is 58%. Fifty-eight percent of 35psi is 20 psi. According to your Rock Warrior document, I should set my pressure to 27psi because 27 with a 25% loss is 20 psi and my TPMS will alert me in time from having a blowout.
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OK, congratulations on finding a tire that supports the "For most cases..." part of your quote. Obviously, not only is that particular tire not germaine to our discussions here in the 200 Series Forum, but is an obvious special case.

I have no idea what you are talking about here:

"According to your Rock Warrior document, I should set my pressure to 27psi because 27 with a 25% loss is 20 psi and my TPMS will alert me in time from having a blowout."

The 17" TRD Alloy Wheel document you reference recommends cold tire pressure for a LT285/70R17 Load Range E tire on an LC200, Tundra or Sequoia. Depending on the generation of the doc in question, that RCTIP is either 40psi (original recommendation found here: Guidelines for the Application of Load and Inflation Tables (Original)) or 46psi (revised recommendation found here: Guidelines for the Application of Load and Inflation Tables (Revised) to conform with the 25% above minimum 35psi TPMS trigger pressure required by FVMSS No. 138). I have no idea where you are getting 27psi.

In any event, you are obviously free to run whatever tire pressure(s) you want. Just be aware that there are well documented safety concerns when running on underinflated tires.

I'm done here.

HTH
 
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You guys constant pissing match over tire pressures provides me great humor!

IMG_0837.webp
 
@Boston Mangler I once borrowed a friend's car and it completely (and dangerously) understeered on the first turn (on ramp). The auto shop had inflated his tires using the "bulge in the sidewall" as their tire pressure gauge. I checked the pressure and they were all about 100 psi. Not much contact patch at 100 psi on a passenger tire!

gaijin said:
Just be aware that there are well documented safety concerns when running on underinflated tires.
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I am only asking for one credible document that states your claim. I agree, underinflated tires are bad. But there's no way all LT tires are underinflated at the same pressure threshold. Your interpretation of a table or chart should not be stated as facts.
 
hoser said:
I am only asking for one credible document that states your claim. I agree, underinflated tires are bad. But there's no way all LT tires are underinflated at the same pressure threshold. Your interpretation of a table or chart should not be stated as facts.
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Agreed, false facts based on BS narratives.
 
Does anyone have the separate tire inflation charts for the HE edition?
 
Haha the 200 section is the only one that has these tire pressure arguments... Maybe that is a good sign that the 200 is so good that there is nothing else to argue about. lol
 
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