You and me, both! I can't ever understand the gear sizes for this or that !!

 

Yes but 4.56's would be way too low for 265/75r16's and taking off faster is the whole reasen i want 4.10's.

 

oh okay gotcha

 

If you had stock size tires or even slighty larger tires and ran a 4:56 gear you would launch faster but as you got up to speed your engine would be screaming(super high rpms). But if you ran 4:10's it would be a livable rpm.
Think of it like this, 4:56 gears with stock tires would be like running in 3rd gear at 55 or higher mph

 

4.11 in the front and 4.10 in the back is fine. as long as it falls within one percent there will be no problem. (also for reference, Jeep wranglers have been using the 4.11/4.10 setup for years.

the bigger the gear, the more you can vary. for example, my Jeep is currently running 5.38 in the front and 5.41 in the rear. no issues what so ever.

 

You guys with the 4.7 have an advantage. You have the 5 speed. At 55 miles per hour you would not be doing too bad. You need your overall gear ratio to find out. I have bee contemplating gears for my 05 with a 3.7L. Gears are the only real performance enhancement for it.

Anyway it is all about RPMs. The five speed final ratio is.67:1 in fifth gear. It is an overdrive. The original poster has 3.55 rear gears and his tire size is 30.6 inches. There are several good calculator tools to find your rpm for a given speed with a given gear ratio. At 55 with the 3.55 gears you should be seeing around 1436.43 RPMs give or take a few. At 55 with the 4.10 gears you should see about 16.58.97 RPMs. With the 4.56 rear gear you will be at 1845.1. The difference is a net gain of 408.67 RPMs if you go with 4.56 from the stock 3.55 rear gears. I think your V8 at 1845.1 RPM is still lumbering along. This assumes you are on flat ground and in fifth gear at 55 MPH.

Now if you drive like a normal person you are at least driving 65 or 70 then you start to see higher RPMs. At 70 you will see about 2348.21. Still not over revving by any means but you are not sipping fuel at this steady RPM.

I have gone crazy with this. Because I have the four speed and my final tranny ratio is slightly higher than the five speed. For me at 55 I would see 1900.18 RPMs with the 4.56. At 70 I would be 2418.41 RPM. This is why I am having so much trouble deciding between 4.10 and 4.56. I believe the 4.56 in town would be optimal. But once you reach true Highway speed it may indeed be "screaming" like you said.

I am no expert on this and these are just numbers on paper. I am try to find people with real world experience to see how they liked their gears.

superdak05: $1600 sounds pretty good for both ends. Did you do anything else besides gears? (like limited slip unit) How do you like the 4.10s?

 

first let me preface this with I have never had a 6cyl dakota, but I have had experience with gears in the past. I can tell you that going from 3.55 to 4.10 is a fairly drastic change and going from 3.55 to 4.56 would scream on the highway

Best and easiest way I can explain it is this:

Get in your truck. look at your rpms at any specific gear/speed preferably higher top end/gear speeds. (55mph to 70mph)

Now, here's a cut down chart. its kinda crude and just shows a 1 to 1 ratio for final drive, but it will give you an estimate of what a gear change will actually do to your RPMS.

Find your current Gear ratio, then RPM. look across the chart to see what it will be with the higher gear set.



again, this is a rough chart and very crude example, but it should put it somewhat in perspective.

A good/easy example for me is a Jeep wrangler 4cyl. has 4.10 gears stock and 29" tires. when tires are changed to 35" a 4.88 gear ratio becomes the factory equivalent of the original ratio. Without tie tire change, top end would be gone, and drivability would be shot.

I know the numerical numbers look like they go in small increments, but keep in mind, they do make drastic changes when you start moving up 2 places on the chart.

Torque will be increased and fuel consumption will suffer, as will top speed.


Also, its not a bad idea to give the guys over at Randy's ring and pinion a call as they are very familiar with the caveats of the wrong gear vs the right one and what your hoping to achieve by swapping.

 

good break down! well we shall see what happens when i decide to get gears!

 

Thanks, that does indeed put it into perspective. I was only looking at the final drive ratio of .67 to 1 which is what the V8 dakata has in 5th gear. At that ratio with 4.56 gears and 55 MPH you would see 1845.1 RPMs. Not too bad. However, what I was failing to look at was the RPMs in lower gear at various speeds. I guess to even figure that out you need to know your shift points and other variables that I am not considering. Also, as I did point out when you go beyond 55 like most of us would do you then start getting into some screaming RPMs.

Your chart is for a 1 to 1 final gear which for both the V8 and V6 Dakota is 3rd gear. For you V8 guys you have 4th gear at .75 to 1 and fifth at .67 to 1. The V6 guys end at 4th gear with a .69 to 1 ratio. Even with that in mind your chart does snap you to attention with the RPM differences between your current gears and what you are contemplating.

For me with the V6 it looks like 4.10s may indeed be the best compromise. Otherwise, it might be like driving a!!!!!

I don't want to hijack this thread from Ruger226 as they just had a simple question, but this is a pretty good discussion. I am sure that there are plenty of threads on the subject if I look. That being said, I think there are enough of us that are still a little clueless of the gear thing. I am very new to this board so I enjoy the fresh info that I may not have considered. I can also bet that a lot of these threads were started toward the beginning of the 3rd generation. There must be more that have done the gears by now that might have more information than before.

Thanks again Ueland for you perspective on this. You have given me one more thing to kick around.