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  #21  
Old 12-15-2010, 12:17 PM
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Originally Posted by AxleIke View Post
but if you are running a 35 and a 35.2, due to pressure difference, no problems will crop up.
I think the pressure difference is meant to do exactly the opposite on an 80...

more air in the back to keep the effective diameter the same as the front when loaded.
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  #22  
Old 12-15-2010, 12:36 PM
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Originally Posted by DaveInDenver View Post
Toyota definitely uses a Torsen-type and I'm pretty sure that I agree totally with you. Just throwing it out there for discussion.
To be clear the US 80 series (most of the references in this thread) had two t-cases, for the FZJ80 a HF2AV w/Viscous Coupling or in the FJ80 the HF2A which only has the diff lock. The Torsen-type were used much later, i.e. your 4R, and are very different systems.

I have heard many discussions about the operation of the Viscous Coupling but I have only seen one situation where a V/C went bad due to different size tires and it was one a Previa All-trac. The customer had replace the tires on the front axle with a different size than the rear. The engineer said there was enough difference in the output shaft speed that the VC was constantly trying to over come the "slipping" it sensed. Initially the V/C would "lock up" (aka hump) while trying to turn tight turns but got worse unitl any turn would do it ( pretty odd sensation at 55 mph ) it was replaced and no further issues.
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  #23  
Old 12-15-2010, 01:24 PM
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... The 100 is a VC, right?
No, I beleive the 100 series use the HF2A t-case like the early 80.
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  #24  
Old 12-15-2010, 02:29 PM
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Originally Posted by rover67 View Post
I think the pressure difference is meant to do exactly the opposite on an 80...

more air in the back to keep the effective diameter the same as the front when loaded.
Sure. I just am saying that say you got to camp and unloaded. Running with the rears over inflated isn't going to hurt anything.
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  #25  
Old 12-15-2010, 03:01 PM
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oh yeah.. no way. I agree.
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  #26  
Old 12-15-2010, 04:33 PM
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Originally Posted by Inukshuk View Post
Will check.

What about the inflation difference for P metric vs. LT. Nitto says:

"Please note that size-for-size, LT-metric tires require higher air pressures to carry equivalent loads of P-metric tires, and that any failure to adjust air pressures to achieve the vehicles load requirement will result in tire fatigue and eventual tire failure due to excessive heat build-up. Due to the higher PSI requirements of LT-metric tires, they may not be suitable for replacing O.E. P-metric tires because of the ride harshness that results from higher PSI requirements.
P265/75R16 114 Max Load = 2,601 lbs @ 35 PSI. In order to carry the equivalent load, a LT265/75R16 Load Range C must be inflated to 50 PSI. Using this
example, even LT265/75R16 Load Range D, or E must be inflated to 50 PSI to carry the P-metric load at
35 PSI. LT tires do not offer any benefits of being "heavy duty" when under-inflated."

http://www.nittotire.com/assets/safe...t%20Trucks.pdf

Not sure about what others do but I typically run around 6-10 psi more in my LT tires than I did with P tires. Most threads I've read stipulate +10 over stock when running LT tires on a vehicle originally placarded for P tires.

The reality is running 42 psi in tires makes the 80 ride like a brick so I've experimented and with my Toyo MTs found that 38 psi for around town driving works best. When loaded for CM etc. and pulling the trailer, I add more air to the rear tires.

Here is another .pdf file with charts etc. for doing the conversion from P to LT tire size.
Attached Images
File Type: pdf Discount Tire - Load Inflation Tables.pdf (114.1 KB, 65 views)
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  #27  
Old 12-15-2010, 05:50 PM
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Neat chart. I'll check that out. I typically ran my BFG A/T's at 36-38.

Now we need some Denver snow so I can see how well they work.

Quote:
Originally Posted by corsair23 View Post
Not sure about what others do but I typically run around 6-10 psi more in my LT tires than I did with P tires. Most threads I've read stipulate +10 over stock when running LT tires on a vehicle originally placarded for P tires.

The reality is running 42 psi in tires makes the 80 ride like a brick so I've experimented and with my Toyo MTs found that 38 psi for around town driving works best. When loaded for CM etc. and pulling the trailer, I add more air to the rear tires.

Here is another .pdf file with charts etc. for doing the conversion from P to LT tire size.
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  #28  
Old 12-16-2010, 10:48 PM
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Originally Posted by corsair23 View Post
Here is another .pdf file with charts etc. for doing the conversion from P to LT tire size.
So, stock for a 1993 FZJ80 is P275/70 R16 114H (owners manual) at 32 PSI per the door jamb sticker, which, for the 114 Load Index you get 2355 as standard load.

My new Nitto Terra Graplers are LT285/75 R16 122/119Q in a "D" Load Range. (I cannot figure out why there are two numbers here "122/119Q" where I think there should be one. This is the Load Index spot, and the Q is the speed rating. anyone know?)

Going to the Discount Tire tables, for the 122 Load Index there is the closest to stock load rating of 2340 in the 40PSI column and for the 119 Load Index there is the closest to stock load rating of 2330 in the 45PSI column.

I will see what 40 PSI rides like.
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  #29  
Old 12-16-2010, 11:16 PM
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Quote:
Originally Posted by Inukshuk View Post
<snip>My new Nitto Terra Graplers are LT285/75 R16 122/119Q in a "D" Load Range. (I cannot figure out why there are two numbers here "122/119Q" where I think there should be one. This is the Load Index spot, and the Q is the speed rating. anyone know?)
Q = 99mph so I dunno. Maybe load for 2 different rim widths?
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  #30  
Old 12-16-2010, 11:59 PM
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Quote:
Originally Posted by Inukshuk View Post
My new Nitto Terra Graplers are LT285/75 R16 122/119Q in a "D" Load Range. (I cannot figure out why there are two numbers here "122/119Q" where I think there should be one. This is the Load Index spot, and the Q is the speed rating. anyone know?)
Dunno about the dual numbers but looking at Nitto's sight for the 285/75R16 D load range they only list 122Q so I'd go with that. Looks like 119Q is for the 265/75R16 D tire
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:

"...anything else i can do for you guys, how about i wash your car or mow your lawn while you figure out your firewall system? I am now boarderline insane/unibomber." Kipper

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