Overdrive or Taller Gears for Fuel Savings

[Bernie]

I posted this in the "no engine, no trans" third gen forum. It kind of belong there (diffs) and here as well (trans).



I have an 06, HO, 6 speed manual 4x4 with 3. 73s. The truck needs another gear at highway speeds! I'm turning about 2400 RPMs just to keep up with traffic at 75 MPH. If I'm late and I need to move, it's even worse.



Please, save the e-mails and posts telling me to slow down. The safest speed is with the traffic around you. If that is 65 MPH, I go 65 MPH. If that is 85 MPH, I do 85. If it's an empty highway, I do about 10 over the posted limited (maybe a little more if I'm late).



I drive about 45k miles a year, mostly highway, so if fuel is $3 a gallon a 3 MPG savings (from 16 to 19) means about $1300 a year.



I have found this overdrive:

http://www.drivetrain.com/new_overd...dodgmanual.html



I figure (with shipping, handling, shortening the drive shaft, and $400 for an install) this unit will cost me about $3700. It will take me three years to pay it off (in fuel savings).



The problem is:

-I want to wait until my warranty is over to modify the truck (2 years)

-Three more years to pay for the unit (truck would then be 5 years old and have 225k miles on it)

-If I keep the truck until 300k miles I've only saved about $2200 in fuel total.



My questions are:

-Has anyone used this overdrive? What do you think? What type of milage do you see?

-Is the final drive of 2. 13 (with my trans and axels) possibly too tall?

-Would it be easier/less expensive to change my diffs out to a taller ratio? Is there a 3. 53 (front and rear)for my truck? I belive I have the 11. 5" rear end.

-Any other thoughts?

 

[Bertram65]

Other thoughts?

If you do not need the truck for all your daily driving get a car that gets decent mileage and save on gas and wear and tear on the truck. It does not have to be a econobox either, used late model Camaros and Corvettes are pretty reasonable and get close to 30mpg on the highway.

 

[BigDan]

Why dont you do like most of us and get taller tires.



I have a 6 speed with 3. 73 and rarely see over 2K rpm with 35's



Ive always had 34-35 on all my trucks even on my 02 6 speed with 4. 10's.



295's are a good choice because the're the same with as stock just taller and you'll get better mileage.



You dont need to lift your truck with either 295 or 35's



There have been many many posts on the cost benifit of aux OD and it truns out you will have to drive something like 300K+ to save a dollar in fuel. Of course this was a few years back when fuel was cheaper.



It sounds like you dont want to void your warranty and it seems now day's dealers have been knowen to void warranty's for off road lights.



Try the taller tires first.



I know what you mean about having to drive fast in certia regions. Out here in CA consider yourself lucky if you can do 65, but when driving back from TX and trying to get the best MPG possable which is at 65mph its hard because big rigs are all going 80mph.

 

[Bertram65]

Why dont you do like most of us and get taller tires.



I have a 6 speed with 3. 73 and rarely see over 2K rpm with 35's



Ive always had 34-35 on all my trucks even on my 02 6 speed with 4. 10's.



295's are a good choice because the're the same with as stock just taller and you'll get better mileage.



You dont need to lift your truck with either 295 or 35's



There have been many many posts on the cost benifit of aux OD and it truns out you will have to drive something like 300K+ to save a dollar in fuel. Of course this was a few years back when fuel was cheaper.



It sounds like you dont want to void your warranty and it seems now day's dealers have been knowen to void warranty's for off road lights.



Try the taller tires first.



I know what you mean about having to drive fast in certia regions. Out here in CA consider yourself lucky if you can do 65, but when driving back from TX and trying to get the best MPG possable which is at 65mph its hard because big rigs are all going 80mph.

The new '06 trucks have the G56 6 speed which is roughly the same gearing as the old NV5600 with 4. 10s, also 295 are wider and taller than the stock tires.

 

[BigDan]

also 295 are wider and taller than the stock tires.

Yeah that's the point taller tire = higher gear ratio = lower crusieing rpm = better mpg.



Yeah I knowthe g56 have a lower 6th gear but its not as bad as my 02HO 6speed 4. 10's close but not as bad. The 295's helped my 02 alot, or you can go with 35's for even lower rpm

 

[DGamelin]

US GEAR is the OD that I would like to have. For a different reason then yours. It has a 22% OD at 75 in OD you would be turning 1875 RPM. That would be great as long as your clutch will hould up. I am not saying it wont, but you know if it gos 85 easly how munch faster are you going to drive it? At 85-90 there is a lot of wind drag let alone its weight, and you're not going to run out of power. I wonder?



04. 5 3500 6x6 Quad cab 6speed 373 25k

93 250 2wd xcab auto 355 240k

 

[KParsons]

tdi

a,jetta tdi will get 50 to 60 mpg. a good used one is 8to10k$.

 

[SKneeland]

a little off topic, but got a speeding ticket yesterday. had the cruise set at 2k rpm..... ticket is for 140km/h (roughly translates into about 87mph) speedo showed about 115



i didnt realize the new 6speed final drive was so low

 

[Bernie]

Other thoughts?

If you do not need the truck for all your daily driving get a car that gets decent mileage and save on gas

Thanks, but I need the truck for my job. I am a firefighter and I call on Fire Departments and sell them the equipment they need to do their job. I often have to carry large amounts of equipment for demonstration and delivery. I don't always need the weight rating of the Dodge 2500, but it is rare that I can see out my back window because the equipment is stacked to the top of my Leer cap.



I have a 1995 BMW 318ti (1. 8 liter, normally aspirated) that gets 32 on the highway that I use for personal stuff.

 

[Bernie]

Why dont you do like most of us and get taller tires.

Thanks, but there are a few things I don't like about taller tires:

-Taller truck! I don't go offroad anymore, so the stock height is overkill.

-Taller truck! More wind resistance .

-Taller tires are heaver and need more power to get them moving.

-Even though I'll be at less RPMs, the additional fuel consumption because of the above items will probably negate the advantage.



Also:

-Taller trucks don't handle as well (not that I bought this truck for its handling). In an emergency maneuver they are more likely to roll over.

-Taller tires are wider, and worse in wet conditions and really bad in snow conditions.

-Taller tires cost more than stock sizes. You buy new gears or an overdrive once, but have to keep buying more expensive taller tires for the time you own the truck.

-Taller tires wear suspension/wheel bearing parts faster.

 

[Bernie]

G56 Compared to NV5600

So, If the above posts are correct, I've been looking at info for the wrong transmission. I was under the impression I had a NV5600 in my truck. If what you guys are saying is correct I have the G56.



I was able to find info on the ratios of a NV5600, but I can't find anything about the G56. Any more info?



Thanks

 

[DGamelin]

The NV5600 has a 0. 730 OD andtheG56 has a 0. 790, G56 has 6% less OD.

 

[RHuby]

I had a Gear Vendor in my last 3 trucks and wouldn't be without one. What I like is the fact that I can cruise at 80 MPH while registering 2K on the tach. Makes a big difference in cab noise. I also pull a 32 ft 5th wheel on long 6% grades, and having all the optional gears available makes an easy job of keeping the CD in the sweet spot. For me, it added an overall average of 3 MPG. While expensive on the buy in, the benefits are really nice if you're going to keep the truck.

 

[Bernie]

G56

I found these ratios online. Are they correct?



1st - 6. 29

2nd - 3. 48

3rd - 2. 10

4th - 1. 38

5th - 1. 00

6th - 0. 79

Rev - 6. 29

 

[GColeman]

US GEAR is the OD that I would like to have. For a different reason then yours. It has a 22% OD at 75 in OD you would be turning 1875 RPM. That would be great as long as your clutch will hould up. I am not saying it wont, but you know if it gos 85 easly how munch faster are you going to drive it? At 85-90 there is a lot of wind drag let alone its weight, and you're not going to run out of power. I wonder?



04. 5 3500 6x6 Quad cab 6speed 373 25k

93 250 2wd xcab auto 355 240k

I ran a US Gear unit for years on my 97 CTD that had 4:11s and NV4500. Splitting gears with a heavy load was great and running at 80mph was easy with the extra OD.

 

[wsurf]

Bernie, I answered in the ' no engine, no trans' forum.

 

[DGamelin]

Yes thoes are the ratio for a G56. I have a NV5600 with 373, I wished I would have looked for 4. 10 it works better with the two speed.