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Discussion Starter · #1 ·
I have wondered about this since I bought the truck and haven't really had time to do any researching but I figured someone here that is a final drive expert would have the answer.

A truck with the off road package has a lower gear ratio on it but then again it has appx 1.5" taller tires which would raise the gear ratio. Anyone have final drive ratios figured out for both? I was thinking maybe Nissan desinged them to be the same.

The other thing too is that the bigger tires would mean more weight which would take more to get the truck moving although it may be offset with the gear ratio.

The non off road trucks have 245/75/17 tires with a differential ratio of 2.94:1

The off road trucks have 285/70/18 tires with a differential ratio of 3.36:1 (I think)
 

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I've read your question several times and I'm still not sure of what your asking. Maybe it's still too early.. :(

Can you rephrase it any to help it make more sense?
 

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The 265/75/18 tires in the standard 4x4 truck and the 285/75/17 on the off road are exactly the same diameter so the 14% gear reduction does lower the final drive gearing in the truck by that amount. You can go to Tirerack.com and look up tire specs. it will show the revs per mile and diam.
 

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Discussion Starter · #4 ·
Sorry for the confusion - I'll try to reword it.

A non OR has a higher (numerically lower) gear ratio of 2.94:1

An offroad truck has a lower (numerically higher) gear ratio of 3.36:1.

1st part of the equation: the OR truck definitely has a lower gear ratio than the non OR truck at the differential.

The 2nd part of the equation is in reference to tire size. It is my understanding that the OR truck has a taller tire than the non OR truck which would also change the final drive ratio. The taller the tire, the lower the gear ratio. Most people say the final drive is at the differential but in fact the gear ratio can also be changed by tire size so in reality the final drive is the tires. This would mean that even though the OR truck has a lower gear ratio at the differential it then has taller tires (than the non OR truck) which means the final drive at the tires would bring the gear ratio closer to the non OR truck.

Hope this helps. If not, anyone else know what I'm referring to?
 
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If you line the wheel/tire set ups side by side (off road and non) you will see virtually no size difference. The off road tire is larger in numbers size, but is also on a 17" wheel vs 18" on non off road.
 

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Discussion Starter · #6 ·
They are a bit different. I went to 1010tires.com and here's what they show on tire sizes:

245/75/17 (non OR tire)= 31.46 inch overall diameter. 661 revolutions per mile.

285/70/18 (OR tire)= 33.7 in overall diameter. 617 revolutions per mile.

That shows to be quite a difference. A little more than 2" taller by their calculations.
 

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Discussion Starter · #8 ·
Maybe we need to confirm tire sizes then.

I have a non OR and just went to check tire size - it is definitely 245/75/17. Can someone verify the OR tire size?
 
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OK, appearantly the XE have different tires. I have a SE, no off road, I just went out in the cold to double check.

265x70x18
 

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Discussion Starter · #10 ·
Well maybe we'll hear from an OR guy to confirm their tire size to. I did mention in my previous post that I wasn't positive about the OR size. We learn something new everyday...

Bill, Here's how the non OR XE and SE model tire sizes compare:

245/75/17 (XE non OR): Diameter is 31.46 inches. 661 revolutions per mile.

265/70/18 (SE non OR): Diameter is 32.6 inches. 638 revolutions per mile.
 
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I wonder if 23 rev per mile is really a significant enough number to really mean anything so far as gear ratio, or even speedometer calibration.
 

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Discussion Starter · #12 ·
That is why I was hoping we had a final drive guru here. Between mine and the OR tire it was showing a difference of around 6.7%. The difference between yours and mine was around 3.3%. The final drive thing can get complictaed sometimes.

I've been looking on the web at final drive calculators but they all seem to want to include trans gearing and transfer case gearing also. I was hoping to find a final drive calculator that assumed a 1:1 ratio into the differntial and using differntial gearing / tire size to figure the new ratio.
 
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To obtain a true ratio, I don't see how you can eliminate the transfer case. I would think that actual ratios will very between 4wd and 2wd with the same rears and tires? Our teannys would remain a constant, but appearantly you not only have the off road vs non off road variance, but also the different models. (XE, SE, LE)
 

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wow, you all are really getting deep into this topic.....cooooool

The transfer case only comes into play when lo range is selected, other then that it's a straight through design. Gear ratios are the same for both 4x4 and 4x2 when the 4x4's are left in hi4 range or 2hi mode.

Now what was the question... :lol: :lol:

I'm completely, totally, 100% exhausted tonight. Been quite a week..
 

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BiXLL said:
What is your tire size JT?
Well let's see.....there are 3 tire sizes available and 2 different rear end ratios.

The 3 tire sizes are:

285/70/17 - OR Package
265/70/18 - Standard 18" tire offered on SE's and LE's
245/75/17 - Standard size on the Steel XE wheels.
 

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my XE OR tire size is 285/70R17
 

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According to a popular tire size calculator the 285/70/17 is 32.7, the 265/70/18 is 32.6 and the 245/75/17 is 31.5.

So all in all the biggest difference we're looking at 1.2" from the XE 17"s and the OR 17's.
 

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if the gears are the same in the trans ,then the drive shaft turns the same amount of time per revolution of the engine. so you can take tire diameter times pie diveded by the axle ratio to determine the distance in inches of inches per 1 drive shaft revolution

ex.
a non OR 245/75R17 has 31.46 in diameter
31.46 x 3.14 \ 2.94 = 33.6 in per 1 drive shaft revolution

a non OR 265/70/18 has 32.6 in dia
32.6 x 3.14 \ 2.94 = 34.8 in per 1 rev

OR with the 285/70/17 with a 32.7 in dia.
32.7 x 3.14 \ 3.36 = 30.55 in per rev

hope this helps a little
 

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SMOKEDYA2 said:
if the gears are the same in the trans ,then the axle turns the same amount of time per revolution of the engine. so you can take tire diameter times pie diveded by the axle ratio to determine the distance in inches of inches per 1 axle revolution

ex.
a non OR 245/75R17 has 31.46 in diameter
31.46 x 3.14 \ 2.94 = 33.6 in per 1 axle revolution

a non OR 265/70/18 has 32.6 in dia
32.6 x 3.14 \ 2.94 = 34.8 in per 1 rev

give me exact # of 285/70/17 and you can figure the OR #'s

hope this helps a little
WOW smoke, you the man!! I'm impressed...
 
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