Educate Me On Axle Ratios

[star2323]

Hey everybody. Explain the differences between axle ratios. Especially 3.73 vs. 4.1 since those are the two sizes which come standard in the 2500 HDs.

[vranasaurus]

Hey everybody. Explain the differences between axle ratios. Especially 3.73 vs. 4.1 since those are the two sizes which come standard in the 2500 HDs.

 

 

The 4.1 is a lower gear than the 3.73 so it is going to be easier on the engine when starting with a heavy load but it is also going to require the engine to turn higher RPM's at highway speeds.

[Zembonez]

The ratio referrs to the difference between input and output shaft rotation.

 

With a 3.73 to 1 ratio, the driveshaft makes 3.73 revolutions to the axle's 1. 4.10 does 4.1 revolutions... and so on. Engine, transmission, etc turn at a higher rpm to go the same speed as the number increases. (or lower as it decreases)

 

Normally this has a direct effect on MPG, but this isn't always the case, It really depends a lot on what you are hauling / pulling.

[star2323]

So the 3.73 should get better gas mileage all other things being the same and the engine is not overworked and the Duramax and 8.1 should perform better with the 3.73 since they have more HP and torque right?

[Wingnut]

Really depends on how you're driving, where you're driving, how fast you drive, how much you tow, etc.

[Daniel T]

still depends on the load...

 

and by the way. the gas mileage difference is on the order of 1-2% according to some tests....

 

with the 6 speed auto tranny, you have overdrive final drive ratios and lock up torque converters, so the mileage difference is almost negligible

 

I have 4:10s in my Burb, and have spoken to folks with the same truck with 3:73 with virtually no differnece in mileage.

[Zembonez]

So the 3.73 should get better gas mileage all other things being the same and the engine is not overworked and the Duramax and 8.1 should perform better with the 3.73 since they have more HP and torque right?

"Should" is a relative term in the truck world. I've given up trying to guess what gets better mileage. Simple matter of fact is that most of the folks in here report between 13 and 17 for their mileage results regardless of engine size. You can expect less if you are towing heavy stuff.

 

4.10s should give you more grunt off the line since that ratio offers the best torque multiplication...

[Kenbow]

If you are towing or planning to tow anything go with the 410, you will not regret it.

[msova2]

Also, the 4.10 has a higher tow rating than the 3.73... (with the 6 liter) The DMAX only comes with the 3.73, but the increase in torque is compensated by the engine

[thecraft]

 

 

Really depends on how you're driving, where you're driving, how fast you drive, how much you tow, etc.

Plus the size of your tires.

[pm26]

I you have a 4.10 gear ratio and install tires that are about 10% larger in diameter than the OEM tires, you are effectively changing your gearing to 3.73. The opposite is true if installing smaller tires.

[star2323]

Thanks everybody.

 

I'm looking at an 8.1 with the 3.73.

[eprovenzano]

I just went through this same deicsion making process. Here is how I boiled it down:

 

4.10 advantages:

- quicker/easier acceleration from stops

- power band is quickly acheived when towing, especially from stops

- reaches the top gear quicker

 

In my opinion most suitable for Urban use especially if towing.

 

 

3.73 advantages:

- lower rpm in top gear for high speed efficiency

 

In my opinnion, most suitable for Highway use, especially if not towing or towing a light RV.

 

So based on your circumstances if you choose the appropriate gear you theoretically should see improved fuel economy, all other things being equal.

 

Good luck!

[eprovenzano]

I you have a 4.10 gear ratio and install tires that are about 10% larger in diameter than the OEM tires, you are effectively changing your gearing to 3.73. The opposite is true if installing smaller tires.

 

I agree. However I'd like to add a word of caution to anyone considering increasing your tire size, if your intention is raising your gear ratio, and improving fuel economy. This will likely back fire. I've found simply increasing the tire size even slightly (say from 265 to 285) will reduce fuel economy. I believe this is due to the extra mass of the tires and the required force required to turn the heavier rubber.

 

Good luck!