Question on P-metric vs. LT tires - 285/70R17's

[proquip]

Hey guys - new to the forum but have been reading and learning a lot! Just bought a new '11 Trail and have been bitten by the mod bug! :naughty:

Looking to upgrade the tires (also looking at lift kits) and I'm leaning towards the Toyo Open Country A/Ts, but can't decide between the P-metric or LT (D load range).

Would there be an appreciable difference in ride quality between the two tires as it relates to the additional unsprung weight of the LT tire (44lbs for P-metric vs. 53 for LT)? I would expect stiffer sidewalls in the LTs, but wondering if the extra weight would also make a difference? Would love to hear from those that have experienced both options. Thanks!

 

[Ryan_S]

I switched the stock tires out to GY Duratrac load E at about 200 miles. I think the ride/handling is much better than the stock tires. Whether that is due to the additional thickness of the sidewalls or just the tire design, I'm not sure.

I will say if I was going for the most MPG I could get, I probably wouldn't get the load E again, they are pretty heavy, and I haven't gotten over 18mpg this winter.

 

[muddyYota]

here's a good read on it, page 2 starts getting into the meat of it about how the LT would be safer and a better choice

"a P-metric tire may be acceptable for a light truck or SUV application, providing the tire offers sufficient load rating (to handle vehicle weight), and providing the vehicle won’t be driven in an off-road situation"

"LT-metric sized tires were specifically developed for use on light trucks, and provide the full tire load capacity that is displayed on the tire sidewall. Because of this, LT-metric sized tires are built very strong and use higher inflation pressures to carry a given load in order to provide the desired safety margin."


P metric = car
LT = truck / suv

If your getting a lift and 285/70 tires. Get some truck tires. End of story.

 

[DEKA3]

I switched the stock tires out to GY Duratrac load E at about 200 miles. I think the ride/handling is much better than the stock tires. Whether that is due to the additional thickness of the sidewalls or just the tire design, I'm not sure.

I will say if I was going for the most MPG I could get, I probably wouldn't get the load E again, they are pretty heavy, and I haven't gotten over 18mpg this winter.

18 MPG? I am getting 13 MPG on the STOCK tires and dont even punch it that much. I do live in NYC btw.... but still a big difference from all the other 4runners ive had in the past.

 

[proquip]

Thanks guys for the input. I should have mentioned that further down the road I'll be looking to get a second set of wheels with meatier tires (duratracs or something similar). I guess I was really focused on a nice riding tire for this first set.

I ordered the P-metric Toyo's and should be on the truck this weekend. I'll post my reaction to the new tires once they're on.

Thanks.

 

[proquip]

Interesting read. According to the article, Toyota designed for ~2,300lbs. load capacity per corner (2,535lbs x .91). Using the same approach, the 285/70/17 P-metrics will still be a step up in load carrying capacity (2,833 x .91 = 2,578lbs) without going all the way up to the 3,195lbs load capacity of a D load range 285/70/17.

Like I mentioned below, these tires will likely not see any severe offroading - they'll see mostly highway miles.


Thanks again for the link.

 

[JB.]

According to the article, Toyota designed for ~2,300lbs. load capacity per corner (2,535lbs x .91). Using the same approach, the 285/70/17 P-metrics will still be a step up in load carrying capacity (2,833 x .91 = 2,578lbs) without going all the way up to the 3,195lbs load capacity of a D load range 285/70/17.

Yes, and that 3195lbs is only achieved after filling to 65psi. To achieve 2300lbs load capacity in LT285/70/17 you need 40lbs of pressure. For 2578lbs, 46psi. Amazingly, the P/LT load/pressure relationship went unmentioned in the article.

Like I mentioned below, these tires will likely not see any severe offroading - they'll see mostly highway miles.

Then P all the way. Better handling, tolerates underinflation better, cost less, higher speed rated, and generally safer.

 

[proquip]

Thanks JB, that's a great point. So in the case of the stock tires (Dueler 684II's), the max load rating of 2,535 is at 44psi. In the case of the 4Runner, Toyota calls for 32psi, so the target design load is 32/44 x 2,533 x .91 = 1,678lbs per corner. In the case of the D-load 285 tires, you'd only need about 52% (1,678/3,195) of it's max load capacity during normal highway driving, which in my mind means it's not being used optimally. I can see however if you air down your tires quite a bit for offroading, or carry heavy loads or tow, then you would want a higher load rated tire.

Thanks.

 

[JB.]

Thanks JB, that's a great point. So in the case of the stock tires (Dueler 684II's), the max load rating of 2,535 is at 44psi. In the case of the 4Runner, Toyota calls for 32psi, so the target design load is 32/44 x 2,533 x .91 = 1,678lbs per corner. In the case of the D-load 285 tires, you'd only need about 52% (1,678/3,195) of it's max load capacity during normal highway driving, which in my mind means it's not being used optimally.

If you want to do it that way, the 44 should be a 35 as the official load carrying capacity of standard load passenger tires stops there. Additional inflation is allowed for special operating conditions - e.g.,speed with high load - but no extra load capacity is assigned.

 

[JB.]

JB--can you explain this one? To the average person, like me, I would never know this. I would interpret it the same way--at 44 PSI, the max load is 2,535 lbs. If I wanted to calculate the max load at 32 PSI, it would make sense to do 32/44 (.73). If we go 32/35 (.91), we're giving way more credit to the load capacity of the tire, right?

The max load is the same at 44psi as it is at 35psi (for a standard load passenger tire which I presume is what came on the truck). You can add some extra pressure past 35psi if you're going to be driving 90mph across Texas, but don't add the extra pressure to carry more load.

There's a load/inflation table linked to in this thread and you might find the whole thread interesting.

LT vs P inflation article - Toyota 4Runner Forum

 

[SeattleMike]

The max load is the same at 44psi as it is at 35psi (for a standard load passenger tire which I presume is what came on the truck). You can add some extra pressure past 35psi if you're going to be driving 90mph across Texas, but don't add the extra pressure to carry more load.

There's a load/inflation table linked to in this thread and you might find the whole thread interesting.

LT vs P inflation article - Toyota 4Runner Forum

I read all that and I just got more confused.

I'm running on stock size "E" rated LT tires at 44 PSI. Is this correct or not?

 

[JB.]

I read all that and I just got more confused.

I'm running on stock size "E" rated LT tires at 44 PSI. Is this correct or not?

Right on the money.

 

[SeattleMike]

Right on the money.

Awesome. Now, based on the both the thread and the pdf file, am I supposed to be adding 10 psi for highway driving (65-75mph) and reduce the load capacity by 10% if I plan on doing more than 75?

 

[Falls]

I personally would never run anything more than a C rated tire on the 4R ....... unless the tire I want comes in a "D" .

I off roaded the heck out of my last runner with 2 sets of "P" rated Revos and although traction is/was not great off road they made it through some narly stuff.

Im currently running "P" rated Firestone Destination AT's in stock size (temp fix to stock tires) but my stepson and I are looking at GY Dura's . He's getting me hooked on them.

Just my .02 , everyone has a tire opinion .

 

[JB.]

Awesome. Now, based on the both the thread and the pdf file, am I supposed to be adding 10 psi for highway driving (65-75mph) and reduce the load capacity by 10% if I plan on doing more than 75?

Sorry, didn't see this.

Yes, if you want to follow things to the letter. Not a bad idea but few do, myself included. I assume those standards come from the commercial trucking industry where frequent, heavy loads are the norm and I'm comfortable not paying too close attention on them.

As I read again what I wrote in that thread, I remember it was from the viewpoint of trying to come to grips with, but resisting, what I had recently learned and verified about the extra pressure requirements of LTs. I didn't want to run 44 or more psi but couldn't see how it could be legitimately avoided, thus the chart, trying to put the situation in context. There's a lot of load reserve with the stock passenger tire size, so even though that reserve goes down a bit with LTs that aren't up to full pressure and violates the idea of not going less than OE, I'm pretty comfortable being in the upper half of a typical OE installation (the chart). I currently run 38psi but am always on the lookout for situations where I think I need more pressure, especially important here in the desert. Just going ahead and using the right pressure from the start, as you're doing, is even better.

As long as people aren't running door sticker pressure on LTs, I don't think it's a huge deal. Most people aren't frequently loading their trucks heavily. I just hate to see people with Ps somewhat reluctantly thinking they need to spend the money on LTs as a highway upgrade or something.

 

[SeattleMike]

Sorry, didn't see this.

Yes, if you want to follow things to the letter. Not a bad idea but few do, myself included. I assume those standards come from the commercial trucking industry where frequent, heavy loads are the norm and I'm comfortable not paying too close attention on them.

As I read again what I wrote in that thread, I remember it was from the viewpoint of trying to come to grips with, but resisting, what I had recently learned and verified about the extra pressure requirements of LTs. I didn't want to run 44 or more psi but couldn't see how it could be legitimately avoided, thus the chart, trying to put the situation in context. There's a lot of load reserve with the stock passenger tire size, so even though that reserve goes down a bit with LTs that aren't up to full pressure and violates the idea of not going less than OE, I'm pretty comfortable being in the upper half of a typical OE installation (the chart). I currently run 38psi but am always on the lookout for situations where I think I need more pressure, especially important here in the desert. Just going ahead and using the right pressure from the start, as you're doing, is even better.

As long as people aren't running door sticker pressure on LTs, I don't think it's a huge deal. Most people aren't frequently loading their trucks heavily. I just hate to see people with Ps somewhat reluctantly thinking they need to spend the money on LTs as a highway upgrade or something.

Thanks. I'll stick with 44+ around town, it helps with the MPGs.

I'm not on the side of pushing LT tires or higher load ratings for most people. I just knew what I needed regarding weather conditions and future weight requirements and purchased accordingly. Now, my wife is thinking of getting a Limited and while I might replace the wheels, the tires will remain P and not LT

 

[Falls]

I also forgot with Revos you have to go "P" metric or "E" (LT) load range .