Tire PSI FJ Cruiser - Load Range E

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Nick1994

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My dad has a 2007 Toyota FJ Cruiser with oversize 285/70-17 BFG All Terrains (basically 33" tires). He got them in Load Range E and it doesn't ride like a truck and actually rides nicely. He runs them at 40 psi now and they wear evenly after a few thousand miles. It sees ALOT of off-road driving, not a lot of mud usually very rough dirt roads/rock roads. He doesn't really care about the ride quality so if it's a little bumpier or softer it doesn't matter, we're just wondering what the optimal PSI is since they are Load Range E. It rarely tows and when it does it's a 1,000 pound trailer so that doesn't matter.
 
This is copied from a thread on ClubXterra.org:

OK, the rule of thumb is that you need, at a minimum, to support ~ 35% of the GVWR at each corner.

For your X, that's about 5,200 lb GVWR, so ~ 1,820 lb per tire.

If the max load for the tire is 2,270 lb, 1820 lb, that's ~ 80% of the tire's max load.

80% of 50 psi (50 psi is the psi NEEDED to support the max weight) = 40 psi.

That means that the MINIMUM psi, for that tire on your rig would be ~ 40 psi, and you were UNDER INFLATED at 35 psi.

Generally, if driving over 60 mph, etc, you add another 5 psi or so to the minimum to help reduce heat build ups, etc....

So, really, 45 psi would probably make the most sense for your use.

An issue to consider is that you are running these tires at 90% of their load capacity.

That's a bit aggressive, and, it means the tire may suffer premature wear/damage more easily than a more lightly loaded tire...and, running at the upper edge of its capacity also means its ride may be a bit bouncy when inflated enough to carry you safely.


So you need the GVWR of the FJ and the max inflation of the tires.

link to the thread if you want to read it all: http://www.clubxterra.org/forums/showthread.php?t=113657
 
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Looking online the GVWR is 5,330 pounds. They are an 80 psi max tire and are capable of 3195 pounds each. So 35% max load per tire is 1865 pounds. So 35% of 80 psi is 28 psi? Sounds like way too low to me.
 
No, 1865/3195 = 58% x 80 psi = 46.6 psi. Add the 5 psi for highway and you're at 50-52.

The psi makes sense, the tires are rated the same as what I have on my 2500HD Duramax. He could try 50 and see how he likes it. No idea where the formula came from. I did it for my Xterra and got 34 and I've been running 35.
 
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Wow, what a bunch of [censored].

First, the pressure vs load curve may be more or less linear, but it isn't directly proportional. I demonstrate that here:

Barry's Tire Tech - Load Tables

And the load tables show that!

Second, I am NOT a fan of the chalk test. Tires aren't necessarily designed to give good footprints, but in EVERY case, the load carrying capacity of a tire IS part of the design.

At the very least, the inflation pressure needs to be capable of generating enough load carrying capacity, and for that you need to consult the load tables.

The right way to do this is to calculate the load carrying capacity of the placard tire size and pressure, then back calculate what pressure is needed to match that. If I have this correct, one version of the 2007 Toyota FJ Cruiser came with P285/70R17's inflated to 32 psi, front and rear. Since this is the same dimensions as was replaced, but a switch from P to LT, it makes the calculation easier - 15 psi more. Making the value, 47 psi.

If the original tire size was different than P285/75R17, the above calculation would need to be adjusted.
 
Originally Posted By: CapriRacer
Wow, what a bunch of [censored].

First, the pressure vs load curve may be more or less linear, but it isn't directly proportional. I demonstrate that here:

Barry's Tire Tech - Load Tables

And the load tables show that!

Second, I am NOT a fan of the chalk test. Tires aren't necessarily designed to give good footprints, but in EVERY case, the load carrying capacity of a tire IS part of the design.

At the very least, the inflation pressure needs to be capable of generating enough load carrying capacity, and for that you need to consult the load tables.

The right way to do this is to calculate the load carrying capacity of the placard tire size and pressure, then back calculate what pressure is needed to match that. If I have this correct, one version of the 2007 Toyota FJ Cruiser came with P285/70R17's inflated to 32 psi, front and rear. Since this is the same dimensions as was replaced, but a switch from P to LT, it makes the calculation easier - 15 psi more. Making the value, 47 psi.

If the original tire size was different than P285/75R17, the above calculation would need to be adjusted.
Thanks for your help CapriRacer! The stock tire size was 265/70-17. So does 47 psi still work?
 
Barry, I spent some time on your website and while much of it is beyond the attention span and understanding of an average car guy you do say something often that I'm curious about. You demonstrate the great difference in rolling resistance in different tires and say one should research them carefully. Where does one find the information to make this comparison and others? Also, is the average guy able to determine an optimal tire pressure or is that a moving target?

thanks
 
Also, if you're in the question answering mood, my Xterra has GVWR of 5200, original tire is 265/70-16 with placard of 30 psi. I replaced with 275/75-16 with rating of 2766@ 44 psi. What psi would be correct?

thanks again
 
Tire pressure can depend on if your on or off road and what off roading you are doing so a one fit answer is not always correct.
 
Originally Posted By: Nick1994
Thanks for your help CapriRacer! The stock tire size was 265/70-17. So does 47 psi still work?


What we really need is the info from the door sticker concerning the tires that came on the vehicle from the factory. Specifically:

Were the factory tires:

1. P or LT rated
2. Size (265/70-17 is correct?)
3. Recommended Cold Tire Inflation Pressure (Front and Rear)

To be on the safe side, it would be helpful to include the front and rear GAWR (Gross Axle Weight Rating)

All this info is on that door jamb sticker and will allow us to recommend a safe tire pressure for your LT285/70-17 tires Load Range E

HTH

P.S. I run those same tires on my Land Cruiser:

ToyotaLC200_2_19JAN13_zps219185e3.jpg
 
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Originally Posted By: gaijinnv
Originally Posted By: Nick1994
Thanks for your help CapriRacer! The stock tire size was 265/70-17. So does 47 psi still work?


What we really need is the info from the door sticker concerning the tires that came on the vehicle from the factory. Specifically:

Were the factory tires:

1. P or LT rated
2. Size (265/70-17 is correct?)
3. Recommended Cold Tire Inflation Pressure (Front and Rear)

To be on the safe side, it would be helpful to include the front and rear GAWR (Gross Axle Weight Rating)

All this info is on that door jamb sticker and will allow us to recommend a safe tire pressure for your LT285/70-17 tires Load Range E

HTH

P.S. I run those same tires on my Land Cruiser:

ToyotaLC200_2_19JAN13_zps219185e3.jpg

Unfortunately, my dad lives 100 miles away in another city. Next time I'm up there I'll look at the placard.
 
Originally Posted By: AZjeff
Barry, I spent some time on your website and while much of it is beyond the attention span and understanding of an average car guy you do say something often that I'm curious about. You demonstrate the great difference in rolling resistance in different tires and say one should research them carefully. Where does one find the information to make this comparison and others? Also, is the average guy able to determine an optimal tire pressure or is that a moving target?

thanks


First, the tire manufacturers are required to publish UTQG ratings on their tires. Those are a good starting point.

Tire Rack has some good comparisons - consumer surveys and their own ratings. Others do as well.

Unfortunately, there is no government requirement to publish rolling resistance. Long explanation on where that stands. So you will only rarely find a comparison.

Tire pressure? Every vehicle sold in the US is required to have a vehicle tire placard that will list the original tire size and the specified inflation pressure for that size. I recommend people use that pressure unless there is some specific reason not to.

For example: Up until 2008, I thought that the amount reserve capacity on tires was too low (as specified by the vehicle tire placard), especially for pickups, SUV's and vans. Plus, I prefer a crisper turn-in. So I used 3 to 5 psi above the placard pressure.

However, starting a few years before 2008, and ending in 2008, the vehicle manufacturers re-evaluated the reserve load capacity and I am now confident in that value. When I get a new vehicle, I may revise my usage pressure.
 
Originally Posted By: Nick1994
Thanks for your help CapriRacer! The stock tire size was 265/70-17. So does 47 psi still work?


According to Tire Guides, the vehicle tire placard ought to say 32 psi as well.

If your dad is using an LT285/70R17, then the math works out to 38 psi.

Please note: That is a different answer, so the methodology makes a difference.
 
Originally Posted By: AZjeff
Also, if you're in the question answering mood, my Xterra has GVWR of 5200, original tire is 265/70-16 with placard of 30 psi. I replaced with 275/75-16 with rating of 2766@ 44 psi. What psi would be correct?

thanks again


A 265/70R16 inflated to 30 psi has a load carrying capacity of 2048#. If you use 275/75R16's then the equivalent pressure would be ........ ah ....... there seems to be a problem. 275/75R16's don't exist - not in P type or LT type!

You did give me the load rating - 2766# - BUT - 44 psi isn't the rating pressure. 35 psi is, (long explanation for that!), but that tells me we are dealing with a P type tire. I looked to see what tire size this could be, but came up empty. I suggest you check that again!

But assuming the values you gave me were correct (Big "IF" there!), then I made an educated estimate, and got a value below 26 psi - which is the lowest pressure I recommend for P type tires.
 
Originally Posted By: CapriRacer
Originally Posted By: AZjeff
Also, if you're in the question answering mood, my Xterra has GVWR of 5200, original tire is 265/70-16 with placard of 30 psi. I replaced with 275/75-16 with rating of 2766@ 44 psi. What psi would be correct?

thanks again


A 265/70R16 inflated to 30 psi has a load carrying capacity of 2048#. If you use 275/75R16's then the equivalent pressure would be ........ ah ....... there seems to be a problem. 275/75R16's don't exist - not in P type or LT type!

You did give me the load rating - 2766# - BUT - 44 psi isn't the rating pressure. 35 psi is, (long explanation for that!), but that tells me we are dealing with a P type tire. I looked to see what tire size this could be, but came up empty. I suggest you check that again!

But assuming the values you gave me were correct (Big "IF" there!), then I made an educated estimate, and got a value below 26 psi - which is the lowest pressure I recommend for P type tires.


OOPS. Cooper AT3 265/75-16 and 2756 @ 44
 
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