rear axle gear ratio

Turtle n Peeps wrote:
Maybe, maybe not. The 3.73 gearing might work out better on some hills where the 4.10's might work out better on others.

This is exactly right.

I think it would be nice to be pulling between 2300 and 2800 rpm.

A 3.73 equipped truck would put excellent power to the ground between 44 and 53 mph in 3rd gear and between 59 and 71 mph in 4th.

The 4.10 equipped truck would pull it's best from 40-49 mph in 3rd and 53-65 mph in 4th. So with a heavy trailer the 4.10 will have an advantage but while running empty and maybe even while loaded on the flats the 3.73 will save a little fuel.


Edit: @2100 rpm the new Cummins is likely able to produce close to 360 Hp so it would still be pulling very well down to 2100 rpm/53 mph in 4th gear.

Anyone ever wonder why just making one thing...gear ratio...changes MTWR and GCWR???


Hotrod..How gears work


How do gears multiply torque?



How does gear ratio affect torque


Wikipedia Gear train

Maybe, maybe not. The 3.73 gearing might work out better on some hills where the 4.10's might work out better on others.

An example: The car I'm driving right now. It started out as a 4.56 car. Then went to a 4.10 car and then a 3.73 gear. Can you guess with gear the car was the quickest with?

I'll give you a hint. The 3.73 gears are in this car to this day. :B

In the above example it is clear the 3.73 gear put more "power" to the rear wheels than the 4.56's contrary to popular belief in what was going to happen.

Turtle n Peeps wrote:
I must have said it here 20 times:
Gears don't make power! In fact, if you want to get technical about it, they make slightly less power.

I have also said this numerous times: Torque is not power. You can have 1,000 ft/lbs of torque of and 0 power out put.

Put a set of 3.00 in you truck and chassis dyno it. Then put a set of 4.56's in and dyno it. Want to bet me a $100 bucks which gear set puts out the most power to the rear wheels? :B

To much work for you? Fine, just dyno your truck in 1st gear and then dyno your truck in 4th gear or whatever gear is closest to a 1 to 1 ratio. What puts out the most power to the rear wheels?

Turtle n Peeps wrote:
I must have said it here 20 times:
Gears don't make power! In fact, if you want to get technical about it, they make slightly less power.

I have also said this numerous times: Torque is not power. You can have 1,000 ft/lbs of torque of and 0 power out put.

Put a set of 3.00 in you truck and chassis dyno it. Then put a set of 4.56's in and dyno it. Want to bet me a $100 bucks which gear set puts out the most power to the rear wheels? :B

To much work for you? Fine, just dyno your truck in 1st gear and then dyno your truck in 4th gear or whatever gear is closest to a 1 to 1 ratio. What puts out the most power to the rear wheels?

You're right on, gears don't make power. . .gears multiply torque. However, under certain conditions pertaining to pulling an RV things aren't always that simple.

Say the OP hooks up his new truck to his 20,000 lb RV and hits his first hill, a 6% grade. It can be determined that 312 Hp are required to be delivered to the rear axle in order for the truck to maintain 50 mph climbing the grade. It can also be determined that at 50 mph with 32" tall tires the rear axle will be turning 525 rpm. In order to have a hope of getting 312 hp to the rear axle while turning it 525 rpm the truck will necessarily be in 3rd gear. With 4.10 gears the engine will be running 2885 rpm. With 3.73 gears the engine would be running 2624 rpm. The engine will definitely be able to make more torque at x2624 rpm than it can at 2885. Without a torque curve for the Cummins it is impossible to know for sure but it looks as if the 4.10 equipped truck could deliver the 312 hp to the rear axle the 3.73 equipped truck could as well. So in this situation both trucks flat out would be capable of delivering exactly the same power and torque to the rear axle.



Edit: to further develop this argument. Consider if the truck could only pull the hill at 48.5 mph. The 4.10 equipped truck would have its full 385 hp available @2800 engine rpm. The 3.73 equipped truck would be able to deliver less power. Steepen the hill to the point where the 3.73 runs flat out in 2nd gear at 2800 rpm and it will be able to deliver more power to the rear axle.

I must have said it here 20 times:
Gears don't make power! In fact, if you want to get technical about it, they make slightly less power.

I have also said this numerous times: Torque is not power. You can have 1,000 ft/lbs of torque of and 0 power out put.

Put a set of 3.00 in you truck and chassis dyno it. Then put a set of 4.56's in and dyno it. Want to bet me a $100 bucks which gear set puts out the most power to the rear wheels? :B

To much work for you? Fine, just dyno your truck in 1st gear and then dyno your truck in 4th gear or whatever gear is closest to a 1 to 1 ratio. What puts out the most power to the rear wheels?

gmc6000 wrote:

tinner12002 wrote:

4x4ord wrote:

tinner12002 wrote:
Go with 4.10s and don't fall for the hype of getting better fuel mileage with the 3.73 because you'll likely not see a difference. With the new trucks they are geared to nearly the same high gear for mileage. I'd also recommend getting the Aisin trans if they have it. Just my opinion.

What do you mean by stating "with the new trucks they are geared to nearly the same high gear for mileage"?

The difference between the 3.73 and the 4.10 trucks, and I'm referring to trucks in the last 3-4 years, I drove was as close as I could tell, 150rpm, not enough to make a significant difference in MPG even as calculated. 3.73s give up about 5-6K pounds of tow capacity also. You can tow with any ratio you want but in my opinion the 4.10s are the way to go. On a straight and level road at 55mph my truck empty will get 22-24mpg and have seen it as high as 25. Hand calculated vs comp was only .5 mpg off so I've checked both ways.

There is no way in hell you are getting 22-24 MPG with a dually truck, unless the straight and level is downhill all the way.

He's cruising the internet. It'll be less when he's out on the hwy.

tinner12002 wrote:

4x4ord wrote:

tinner12002 wrote:
Go with 4.10s and don't fall for the hype of getting better fuel mileage with the 3.73 because you'll likely not see a difference. With the new trucks they are geared to nearly the same high gear for mileage. I'd also recommend getting the Aisin trans if they have it. Just my opinion.

What do you mean by stating "with the new trucks they are geared to nearly the same high gear for mileage"?

The difference between the 3.73 and the 4.10 trucks, and I'm referring to trucks in the last 3-4 years, I drove was as close as I could tell, 150rpm, not enough to make a significant difference in MPG even as calculated. 3.73s give up about 5-6K pounds of tow capacity also. You can tow with any ratio you want but in my opinion the 4.10s are the way to go. On a straight and level road at 55mph my truck empty will get 22-24mpg and have seen it as high as 25. Hand calculated vs comp was only .5 mpg off so I've checked both ways.

There is no way in hell you are getting 22-24 MPG with a dually truck, unless the straight and level is downhill all the way.

Torque multiplication

4.10 delivers more power to the rear axle than does a 3.73 diff....that needs a little explaining.

Most diff ratios offered are about 10% apart...meaning about 10% more or less
power delivered to the drive axles...meaning that going from a
3.73 to 4.1 will have MORE power delivered...or going from a 4.1
to a 3.73 will have LESS power delivered

Sure, the new close ratio trannies does have lower first than before, because
they can with those extra gears...but going too low numerically on the diff can
have higher stresses on the diff gear teeth...'can', not for sure...it depends

Since new gear boxes has more gears and are close ratio...they on the other
end of 1st gear...has double OD's on most...so if me, I'd go lower (higher
numeric) diff ratios