- Thread starter
- #21
"Size-for-size, compared to P-metric tires, LT tires require higher air pressures to carry equivalent loads."
From this article
Tire Pressure for Rock Warriors with LT285/70/17, Load range Es?
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"Size-for-size, compared to P-metric tires, LT tires require higher air pressures to carry equivalent loads."
From this article
gaijin
GOLD Star
That LC sticker has the same info I posted - 33psi for the standard P285/60-18 tires = 2,512 pounds Load Limit
That Tundra sticker also has P-Rated tires - 33psi for P275/65-18 tires = 2,535 pounds Load Limit (Rear) and 30psi for P275/65-18 tires = 2,421 pounds Load Limit (Front)
Not sure I understand the point you are making here ...
gaijin
GOLD Star
I'd love to see that sticker because I worked with my local Toyota dealer all the way up to national parts and could not find the part number cited. I found 3 different stickers - all had incorrect spare tire sizes, but all did have the 46psi recommended pressure for the LT285/70-18 tires.
But I still maintain that recommended pressure is incorrect.
Did they do the math wrong? Not sure what went wrong with their calcs - or even if it was marketing driven. All I know is the science.
gaijin
GOLD Star
Honestly, I'm not sure what the author is trying to say with that statement.
Does it mean that if we had two tires of the same size, one P-Rated and one LT-Rated, that the LT-Rated tire would have to be inflated to a higher pressure to have the same load carrying capacity?
If that's the case, then it appears to be true.
Here's an example of two tires, same size, one P-Rated and one LT-Rated (I chose the LT285/70-17 size for consistency)
P-Rated tire: P285/70-17 @ 35psi = 2,833 pounds Load Limit
LT-Rated tire: LT285/70-17 @ 35psi = 2,105 pounds Load Limit x 1.1 (adjustment for P-Rated application) = 2,315.5 pounds Load Limit.
In this hypothetical case, if we were replacing P-Rated P285/70-17 tires with LT-Rated LT285/70-17 tires, we would have to inflate the LT-Rated tires to approximately 47psi (2,576 pounds x 1.1 = 2,833.6 pounds) to achieve the same load carrying capacity as the P-Rated tires @ 35psi (2,833 pounds).
Again, still not sure what bearing this has on our current discussion.
We are talking about replacing one size of P-Rated tires (P285/60-18) with a different size of LT-Rated tires (LT285/70-17).
In our case it is P285/60-18 tires @ 33psi = 2,512 pounds of load carrying capacity and LT285/70-17 tires @ 39.3psi = 2,286 pounds (adjusted for a P-Rated application 2,286 x 1.1 = 2,514.6 pounds of load carrying capacity)
Even in our case, with different sized tires, your quoted statement is still true - for the same application the LT-Rated tire requires a higher pressure - but it is coincidental because of the different sizes involved.
Did you have a particular point with that quote that I'm missing?
- Thread starter
- #25
i should have quoted the previous post because that was what I was responding to but I was just showing the GVWRs of an LC and a Crew Cab 4x4 Tundra, a Rock Warrior edition to be precise, to show that the GVWR for the LC is higher and therefore wouldn't require less pressure.
Thays exactly what i was thinking. If toyota recomends 46 for a lighter tundra why heavier LC would need lower psi for a bigger load per tire? Unless we say toyota was wrong. I dont think i would like driving with psi of 50.. unless trd tundra had a different suspension..
- Thread starter
- #27
I don't want to post the guys name and drag him into this but maybe he will see this and post a picture of it but this was his response to my PM:
"According to my MDC label 00602-60110
46 PSI all around. Based on a LT285/70R17
Funny thing is, they label the spare as a P285/60R18 (assuming the stock spare) and that is 33 PSI."
- Thread starter
- #28
Thats exactly what the author was saying, I was just responding to the comment quoted and pointing him to an article that explained it.
Markuson
SILVER Star
This thread is making me melon hurt... 
- Thread starter
- #30
Pretty sure it has to do with that factor of 1.1. If you take that out of your equation you get 46. Im wondering if that wasnt already factored in, based on the highlighted part of this section of the article I linked.....
P vs. LT
Although originally developed for cars, most vans, pickups and SUVs are used primarily to carry passengers and P-metric tires are typically lighter, with lower rolling resistance and less aggressive tread designs than typical LT-metric tires.
The combination of better ride, greater fuel efficiency and less noise has resulted in P-metric tires being used extensively for light truck applications. However, vans, pickup trucks and SUVs typically have a higher center of gravity and greater probability of being overloaded than passenger cars.
In order to accommodate this, vehicle engineers are required by Federal Motor Vehicle Safety Standards to specify P-metric sized tires rated to carry 10% more weight than would be required if they were used on a passenger car. This is the equivalent of dividing the tire’s sidewall branded load capacity by 1.10. For example, a P265/75R16 114S tire has a maximum load rating of 2,601 lbs. at 35 psi. However, when this tire is installed on a light truck, the load rating is reduced by a factor of 1.10 to 2,365 lbs. at 35 psi.
So the same exact tire can have two different "load ratings", even at the same PSI. It depends on if its mounted on a Passenger Car or a Light Truck/SUV.
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gaijin
GOLD Star
That's exactly what I've been saying.
The Toyota recommended pressure for the OEM P285/60-18 tires results in a load carrying capacity of 2,512 pounds which is 10% higher than it would be if it were mounted on a passenger car. So, at 33 psi 2,512 / 1.1 = 2,283 pounds which is the unadjusted load carrying requirement for the Land Cruiser.
Therefore ...
We do not have to increase the LT-Rated LT285/70-17 load carrying capacity because it is being installed on a truck. So, at 39.3 psi = 2,286 pounds which is the same as the unadjusted load carrying capacity of the P-Rated tire.
Here it is in a nutshell:
The load carrying capacity required for tires on the Land Cruiser is 2,283 pounds per tire.
Since the Land Cruiser is not a passenger car, if P-Rated tires are installed, this load carrying capacity must be increased by 10% (2,283 X 1.1 = 2,512 pounds. To meet that load limit for P285/60-18 tires, 33 psi is required.
But, if we install LT-Rated tires, which are designed to be installed on trucks, no adjustment to the load carrying capacity is required - it can stay at 2,283 pounds. To meet that load limit for LT285/70-17 tires, 39.3psi is required.
Clear as ... mud, right?
gaijin
GOLD Star
One final thought.
Bearing all the discussion above in mind, just for the sake of discussion, if the 46psi figure were correct for the LT285/70-17 tires, what should the correct pressure be for the OEM P285/60-18 tires?
LT285/70-17 @ 46psi = 2,550 pounds load carrying capacity
P-Rated tires must be increased by 10% so 2,550 x 1.1 = 2,805 pounds load carrying capacity.
OOPS!!!
Max load on those OEM tires is only 2,601 pounds @ 35psi - not possible.
So either the sticker on the door jamb is incorrect for the OEM P-Rated tires, or the fudged number for the LT285/70-17 tires in incorrect. My money's on the latter.
HTH
Bearing all the discussion above in mind, just for the sake of discussion, if the 46psi figure were correct for the LT285/70-17 tires, what should the correct pressure be for the OEM P285/60-18 tires?
LT285/70-17 @ 46psi = 2,550 pounds load carrying capacity
P-Rated tires must be increased by 10% so 2,550 x 1.1 = 2,805 pounds load carrying capacity.
OOPS!!!
Max load on those OEM tires is only 2,601 pounds @ 35psi - not possible.
So either the sticker on the door jamb is incorrect for the OEM P-Rated tires, or the fudged number for the LT285/70-17 tires in incorrect. My money's on the latter.
HTH
I understand that this thread is about E rated tires. Gaijin introduced P rated considerations. When I added a set of 17" RW wheels I elected, somewhat at odds with the typical choice, to install P rated Toyo AT2 tires in the recommended 285 size. When we looked at the load rating charts we concluded that I might be about to run about 30 psi and be in conformance. I started at 30 and gradually moved to 33 based on chalk tests and tire shoulder wear. 33 seems to work well. Now, please realize that this applies to my lightly loaded rig used most on the street. I recently returned from Ouray and after 5000 miles the tires showed no appreciable wear and maintained their Road Force balance. Yes, I realize that my sidewalls are somewhat more at risk than with E rated tires. It is all a tradeoff.
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I ordered the tire inflation sticker this week for the Land Cruiser. It was $1. Plan to use my 15% off coupon. This should help when I go to any tire place from adjusting them down to 33 every time.
I'm going to set them to 44-46 since I have the Rock Warriors and LT 34x10.5x17 and ARB bumpers, winch, drawers, Fridge, roof rack, extra battery.
They seem to fluctuate with temperature here at sea level a couple of pounds when they get hot verses ambient.
It is odd that the spare is still shown lower at 33 on sticker. I throw that out there as the next topic to discuss/debate. Go.
I'm going to set them to 44-46 since I have the Rock Warriors and LT 34x10.5x17 and ARB bumpers, winch, drawers, Fridge, roof rack, extra battery.
They seem to fluctuate with temperature here at sea level a couple of pounds when they get hot verses ambient.
It is odd that the spare is still shown lower at 33 on sticker. I throw that out there as the next topic to discuss/debate. Go.
gaijin
GOLD Star
Spare is shown as the OEM P-Rated P285/60R18 for which the recommended pressure has always been 33psi - so that part is not odd at all.
HTH
So they assume you upgrade your 4 wheels to RW and not your spare? That's lame.
- Thread starter
- #38
10-4, got it. But there can be other factors involved in coming up with a recommended tire pressure. Would you happen to have the Load Limit Table for the LT265/70R16 E 121? The reason I ask is because that is the tire fitted to the 16" TRD wheel for the Tacoma, a BFG AT KO with same load rating as the BFG LT tires we are discussing. The Tacomas GVWR is only 5500 pounds, but Toyota recommends 46 PSI for that application also. Im guessing that tire at that PSI is going to give a load rating well above what the Tacoma requires. But they obviously came up with 46 for some reason. Maybe it has to do with some peculiarity of the TRD wheel/tire combo?
The RW technically doesn't fit the stock spare mount (requires minor modification as has been discussed elsewhere) so Toyota may not officially consider the RW sized spare... I wouldn't consider running two different size tires on a full-time 4WD vehicle and find it odd that they do.
gaijin
GOLD Star
I guess (and I use that verb advisedly) that if one were to order the RW wheels/tires as a port installed option when purchasing a new vehicle, one would get 4 RW wheels/tires mounted and the stock spare would remain. As stated, probably because the RW wheel/tire combo does not fit in the spare tire location without some minor modifications.
Yes, I agree that's lame. And yes, I agree that I would not want to run a different sized spare - and I don't.
It's a shame the RW wheels are not a factory option - the label and spare tire anomalies would probably not exist. However, the RW wheels/tires are probably not offered as a factory option in Japan because they don't meet the strict Japanese road laws.
HTH
