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Old 02-24-2014, 10:51 PM   #1
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Rear axle ratio explained

Can somebody please clarify something that I hope a few other than me don't understand? What is the rear axel ratio and discussion all about?

3.36, 3.73, 4.10?

I drive a 2010 Nissan Armada SE 4x4 with a 3.36, what does that mean? How does that relate to the towing capacity? Along that line, how does torque and HP play in? I mean each measurement of torque is at a different RPM, so how do you compare?

Can I put a larger axel on my Armada to change the ratio?

Ok, that is a lot of questions, sorry.
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Old 02-25-2014, 12:43 AM   #2
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Google it

Several articles regarding this on the net.
This one probably one of the better explanations.
All About Axle Gears - Car Craft Magazine

Bottom line is the lower your overall gearing I.E. 4:10 ratio rather than a 3:23 will give you more pulling power (torque) but worse mileage. You typically want to gear the vehicle to run in the sweet spot of your torque curve of your engine at cruise speed this will enable you to pull grades without constantly downshifting to a lower transmission gear to compensate the rear ends tall gearing I.E. 3:23 ratio. Most manufacturers settle for a middle of the road compromise for favorable numbers on advertised mileage and emissions. Gearing a vehicle correctly for a given application can make all the difference in the world. Just do the research and the math prior to spending money however.

Good luck!
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Old 02-25-2014, 05:13 AM   #3
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The number represents the number of times the driveshaft turns (input) to the number of times the axle turns.(output) The higher the number, the more times the engine rotates to move the vehicle. A higher number produces more torque because the engine fires more times per tire rotation. This also reduces MPG. The torque (power) curve of the engine and transmission gearing/shifting is factored into a differential ratio selection. The number does not affect the load capacity of the axle, tires, hitch, or frame, so don't think a higher number increases your tow vehicles towing capacity.
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Old 02-25-2014, 07:30 AM   #4
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Its not only about the rear end ratio. In a vehicle like yours you may not even be able to change the ratio. And if you did you would need to do it in both the front and back gear sets as you have a 4x4. Today there are a lot of other factors engineer into the truck including computers and sensors along with 6 speed trannies as opposed to 3 speed. Back in the day of a A truck a v8 and a rear end it may have come with say a 3.42. You could change the gear set to get to a 3.73 or a 4.10. Engines have a torque curve.they may put out more or max torque at 3500 rpms. A base truck with a 3.42 gear may have you running 2000 rpm but only part way up the torque curve at highway speed. Its designed for the average user and decent gas milage. Putting a trailer package on it from the dealer may give a 3.73 ratio now. It may run at 3200 rpms at highway speed closer to the top of the max torque curve. Sop as I stated its not just about gear ratio. You need to have a proper match and know the torque curve of that engine. Some engines torque curve looks like a nice bell curve other may ramp up nicely and drop like a stone after a certain rpm. If you put too high a ratio with the engine I last discribed you may run at 4000 rpm and have all revs and no torque. Typically you will loose gas milage as well which is not a problem for a TV but if you are trying to mod a daily driver this may also be a factor.
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Old 02-25-2014, 07:38 AM   #5
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Another factor in the rear axle ratio is the diameter of the drive tires. Larger tires mean fewer revs per mile and smaler means more revs per mile.

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Old 02-25-2014, 08:11 AM   #6
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Another factor in the rear axle ratio is the diameter of the drive tires. Larger tires mean fewer revs per mile and smaler means more revs per mile.

Ken
Yes that is correct and you could get a better ratio for towing with smaller tire. Not recommend though. In todays new vehicles with traction control and computers not only would it mess up your speedo but also your computers for slip control etc.

So that brings up another reason not to change your gearing. You would also need to change the gear in or at the tranny on the speedometer cable. I have done it and seen it done on GM and Ford truck. Not sure how or if this could be done on a Nissan. It would be cheaper and easier to trade it. Or live with it the way it is.
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Old 02-25-2014, 08:12 AM   #7
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Get a real truck.
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Old 02-25-2014, 12:11 PM   #8
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Just get a Ram 3500 dually 850lb TQ and a 4.10.
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Old 02-26-2014, 11:36 AM   #9
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Can I put a larger axel on my Armada to change the ratio?
Maybe, maybe not. As CanadianCrew explained, it's gets complicated because of all the computer-controlled things in your drivetrain. ABS, sway control, traction control and others. Since your Armada is a Titan with a station wagon body, your Nissan dealer's expert tech can probably change your computer program in the ECU (electronic control unit or computer) to allow any axle ratio that's available in the Titan. Only a qualified Nissan tech would know for sure.

If it can be done with a flash to the ECU, then you don't literally change the axle, you change the ring gear and pinion in both the front and rear differentials. But you'd still be limited to whatever axle ratios were available in the Titan unless you paid big bucks for a custom ECU program from a programming guru that would allow your choice of ratio without screwing up the electronic controls in your drivetrain. And then you'd be limited to whatever aftermarket ring gear and pinion ratios were available from some place such as Randy's Ring & Pinion

Note that for 4x4 Titans, they have front ratios of 2.94 and 3.36. So if you already have 3.36 ratio, then you'll have to find a different source to get a ratio with shorter legs. If you have 2.94 now, then the 3.36 would give you a 14% change.

For more tech talk, the axle ratio tells you the number of engine revolutions required for each revolution of your axle only when the tranny is in direct drive (1 to 1 ratio). When the tranny is in overdrive, then it requires fewer engine revs to make one rev of the axle. For example, one 5-speed automatic tranny has ratios of 3.11, 2.22, 1.55, 1.00 and 0.74. So with a 3.55 axle ratio, only when the tranny is in the 1.00 ratio will the engine turn over 3.55 times for each one turn of the axle.
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Old 02-26-2014, 01:42 PM   #10
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The rating of axles is usually done by checking the oil temperature created by pressures on the gears. The higher rating of higher geared housing gets the nod.
It can be modified by changing the oil to higher pressure and temperature rating. I had a GM housing that was bad for overheating the oil under load so synthetic gear oil was the solution.
Even driving while in lower gear to increase torque does nothing to change load on housing.
Most load capacity for TV is based on cooling capacity and mechanical modifications has to be done keeping that thought in mind.
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Old 02-26-2014, 02:23 PM   #11
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If you have the 3.36, then you already have the big tow package, which also included a rear leveling suspension and a beefier tranny cooler with a guage in the dash i believe. You should be fine to tow your trailer, the 5.6L has the best low end torque among 1/2 ton trucks of that generation. If you tow all the time, they sell different ring and pinions for the titan, they probably fit the armada too. The armada also has a 5 speed tranny, keep that in mind if people are telling you to buy 4:10 or 3.73 gears, those ratios were more for ford and chevy owners with a 4 speed transmission. Though, if you tow alot, almost full time. 3.73 gears might serve you well.
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Old 02-26-2014, 10:01 PM   #12
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I was at a week rally last summer and saw a 14000 gvwr 5th wheel towed buy a Titan. He did have airbags and proper tires and to my surprise he took off and his truck handled it very well.
My only thought at the time was that he had to be a Nissan dealer, cause no one else would get that truck to tow that unit.
If I see him again this summer I will surely be talking with him.
He might have the new diesel then.
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Old 02-27-2014, 07:24 AM   #13
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I was at a week rally last summer and saw a 14000 gvwr 5th wheel towed buy a Titan. He did have airbags and proper tires and to my surprise he took off and his truck handled it very well.
My only thought at the time was that he had to be a Nissan dealer, cause no one else would get that truck to tow that unit.
If I see him again this summer I will surely be talking with him.
He might have the new diesel then.
I've seen a titan towing a 5th wheel, the newer 08+ titans had payload capacities at about 1800-2000lbs if i remember correctly. They can technically handle lighter 5th wheels. But he's really overloaded with a 14000lb GVWR 5th.
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Old 02-27-2014, 08:17 AM   #14
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Sorry but 3.36:1 gears are not towing gears, they're highway gears meant to get maximum MPG and are not for towing. For towing you'll want gears of at least 3.75:1. The trade off with the lower gears (higher ratio) is that you're fuel economy will suffer. For example on my Dodge Dakota with 3.55:1 highway gears I would have had a towing cap of 5000lbs. but with the towing gears of 3.95:1 I have in mine I have a towing cap of 7000lbs.
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