Tire PSI FJ Cruiser - Load Range E

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Originally Posted By: Miller88
So what would you recommend for a ~3500 pound Jeep Cherokee with LT 235/85-16 on it? E rated.


A little more info please. Model year? What does the vehicle placard say for original tire size and inflation pressure?

And one last word of note: The pressures I am calculating would be for street usage. They would be different for off road usage or for racing purposes.
 
Originally Posted By: AZjeff
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



Ah ...... Mmmmmmmm ........

I don't see on Cooper's web site that they make a P type AT3 in a 265/75R16. They list 2 LT's - LR C and LR E.

I did find it on Sears' web site, but it appears to be discontinued.

Nevertheless, I get below 26 psi, and 26 psi is the lowest pressure i recommend for street usage.
 
I realize all "P" type tires are max load rated at 35 psi, even though many are max pressure rated for 44 or even 51 psi. It seems that a tire inflated to max pressure would be able to support much more that the rated load. Never understood the reason for having the higher max pressure listed on the tire, when they are load rated for 35? Why are they not load rated at 44 or 51 psi? LT tires are. After all it is the volume and pressure that supports the load even if it was a balloon.
 
Last edited:
Originally Posted By: CapriRacer



I don't see on Cooper's web site that they make a P type AT3 in a 265/75R16. They list 2 LT's - LR C and LR E.

I did find it on Sears' web site, but it appears to be discontinued.

Nevertheless, I get below 26 psi, and 26 psi is the lowest pressure i recommend for street usage.


Go to: http://us.coopertire.com/Tires/Sport-Utility/Discoverer-A-T3.aspx
and look at tire sizes & specs

Here's a cut/paste:


265/75R16 116T 560 A B STD OWL 7 - 9 7.5 10.5 31.57 7.72 2756 14
 
Cooper AT3 265/75-16 Nov 2014 born-on date

b5e3cf4a-8177-454c-88c6-59b43859d578_zpsvtlq1evs.jpg
 
Originally Posted By: CapriRacer
Originally Posted By: Miller88
So what would you recommend for a ~3500 pound Jeep Cherokee with LT 235/85-16 on it? E rated.


A little more info please. Model year? What does the vehicle placard say for original tire size and inflation pressure?

And one last word of note: The pressures I am calculating would be for street usage. They would be different for off road usage or for racing purposes.



It's a 2000 Jeep Cherokee. Placard says 32 for the original equipment Goodyear Wrangler RT/S P215/75-15.

I generally drop to 15 off road to get a bit better sidewall flex.
 
Originally Posted By: Miller88
Originally Posted By: CapriRacer
Originally Posted By: Miller88
So what would you recommend for a ~3500 pound Jeep Cherokee with LT 235/85-16 on it? E rated.


A little more info please. Model year? What does the vehicle placard say for original tire size and inflation pressure?

And one last word of note: The pressures I am calculating would be for street usage. They would be different for off road usage or for racing purposes.



It's a 2000 Jeep Cherokee. Placard says 32 for the original equipment Goodyear Wrangler RT/S P215/75-15.

I generally drop to 15 off road to get a bit better sidewall flex.


OK, at 32 psi a P215/75R15 has a load carrying capacity of 1664# - an then adjusting by 1.1 for light truck usage = 1513#.

In order to carry the same load, an LT235/85R16 needs to use ....... ah ......Mmmmmmm, well the value is below 35 psi, which is the smallest inflation pressure I think should be used for LT tires.
 
There has to be more to inflation pressure than trying to match it up to load/inflation tables. When you look through all the different makes, models, weights, pressure, and optional tire sizes in Tire Guides, the pressures are all over the map. For example a Chevy truck comparing the standard 245/70-17 108 load, and optional 265/70-17 113 load they list the same 35 psi for a 6800 GVW. That's a 330 pound difference per tire in load capacity for the same vehicle. Some Jeeps spec 29 psi on a LT tire. Why so many difference in pressures other that weight?
 
Last edited:
Originally Posted By: AZjeff
So sorry to hijack your thread OP, but this is good stuff.

Barry, is there a formula you use for the inflation pressure for a non-oem spec tire or is it part black art?


There is a formula for inflation pressure vs load carrying capacity, but it is so complex, it is always shown as a table.


Originally Posted By: Traction
There has to be more to inflation pressure than trying to match it up to load/inflation tables. When you look through all the different makes, models, weights, pressure, and optional tire sizes in Tire Guides, the pressures are all over the map. For example a Chevy truck comparing the standard 245/70-17 108 load, and optional 265/70-17 113 load they list the same 35 psi for a 6800 GVW. That's a 330 pound difference per tire in load capacity for the same vehicle. Some Jeeps spec 29 psi on a LT tire. Why so many difference in pressures other that weight?


There is more to it.

First step is matching the load carrying capacity.

Second step is: If the calculated inflation pressure is LOWER than the spec inflation pressure, use the placard pressure.

And some Jeeps specify 29 psi for an LT tire? Not exactly. The tire in question is a Flotation tire, which is a bit different than an LT metric - and a different set of rules apply to those kinds of tires.
 
Okay, another 09 Chevy truck example. 265/70-17 113S 35psi. With the optional tire with a lower load index, 275/55-20 111S 30psi. Why are they different?
 
Back to the OP's original question, I think 32 psi would be more than enough for the bigger tire, since an optional tire for the FJ Cruiser is LT 265/75-16 D 116S at 32 psi.
 
Originally Posted By: CapriRacer
Originally Posted By: Miller88
Originally Posted By: CapriRacer
Originally Posted By: Miller88
So what would you recommend for a ~3500 pound Jeep Cherokee with LT 235/85-16 on it? E rated.


A little more info please. Model year? What does the vehicle placard say for original tire size and inflation pressure?

And one last word of note: The pressures I am calculating would be for street usage. They would be different for off road usage or for racing purposes.



It's a 2000 Jeep Cherokee. Placard says 32 for the original equipment Goodyear Wrangler RT/S P215/75-15.

I generally drop to 15 off road to get a bit better sidewall flex.


OK, at 32 psi a P215/75R15 has a load carrying capacity of 1664# - an then adjusting by 1.1 for light truck usage = 1513#.

In order to carry the same load, an LT235/85R16 needs to use ....... ah ......Mmmmmmm, well the value is below 35 psi, which is the smallest inflation pressure I think should be used for LT tires.


I bumped these up to 35 and they don't seem to want to destroy the Jeep. My last tires were also load range E but on Bridgestone M775 carcasses - those things at anything above 28 would just beat the living daylights out of the Jeep. These tires at 35(cooper carcasses) don't seem to be near as hard as the old ones at 29.

Unfortunately, I have a bad valve stem ... so looks like I am going to have to break it down and change a valve stem.
 
Originally Posted By: Miller88
So what would you recommend for a ~3500 pound Jeep Cherokee with LT 235/85-16 on it? E rated.


I'll add my recent experience w/ LR E and inflation.

I recently selected BFG Commercial Traction TA A/T tires in 235/85r-16 for my French spec LR90, (later sold as a Defender here), ~3,600 lbs GVW. After reading various opinions on E tires on lighter vehicles, I had some concerns and contacted BFG directly. After getting shuffled around a bit, I received an email that stated something to the effect of '...factory inflation pressures are acceptable for you application...the tires will air down for sand...nice truck...'

Been running the recommended road and soft surface pressures w/o any problems.
 
Lol poor CapriRacer getting drilled for pressure recommendations.

Thanks CapriRacer! You're always here to the rescue on our tire questions!
 
Originally Posted By: wings&wheels
Originally Posted By: Miller88
Tall and skinny tires unite!


Long Live the 7.50x16
laugh.gif



I was considering a set of 7.50-16 for the Cheorkee! The problem was it would have been a bit taller than I can run with the gearing I have right now. I didn't want to drop $1000 on a set of tires, then have to drop $1200 to get the axles regeared.
 
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