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?
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.
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?
Unless the law has changed (see it here:
Tire Safety Information, Final Rule. ) there has to be a label somewhere showing recommended tire pressures:
- 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
