Thinking of starting to build up my axles. Im leaning towards the 5.13's. Ive got 40's now, possibly going to go bigger in the future. The 4.56's would probably work for the 40's but any bigger and I'm worried I'll wish I had gone lower.
Im thinking 5.13's lock the rear, and posi unit for the front. I dont want to lock the front, ive had/heard bad experience from it and I think that a posi will prevent breakage right??
The truck will still be driven on the road, so what am I lookin at for a top speed here with 5.13's? Guessing around 55-60 at 2500-3000 rpm. (ive got a 4-speed man. with 205)

 

I swapped out the 3:55's in my truck with 4:88's. I have 38 inch Hawgs and I think I wish I had gone with 4:56's. I dont have a tach but my motor sounds like its revving way high at anything over 70 mph and when I left off the gas any it starts slowing down real fast as if I just down shifted. My truck has a c6 though so Im not sure how much difference that would make. Im hoping 40 or 42 inch tires will make it seem better. It does got gobs of bottom end now I just dont like driving it on the interstate now.

 

i think 4.88's would be wise...

 

Some will say that there is no such thing as overgearing, but I disagree. I like them to have some highway capability. I also think that 4.88s would be good.

 

I'm running 4.88's with 41's. Thats just about right for street and offroad. If the truck was all offroad I would would go to 5.13's.

 

This probably has more to do with actual application rather than what others are running and what some believe to be reasonable.
Here is what I mean:
You have a 4 speed, which means that you already have a pretty low first gear and a reasonably low second gear. This can be better than an auto and would be capable of using a higher ratio (numerically lower).
While the auto will still have a 1:1 final rive ratio, and it will slip at cruise speed, it will have some HP losses, and require a little more gear.
You also have to consider that you are running 40" Ground Hawgs right? These are not a true 40" tire. SInce they are undersized, you should be considering the gearing for a
37.5" to 38" tire.
Perhaps this would make a difference. You also have to consider the powe you are making. Even a 38" tire might require a real deep gear if it were to be powered by a little 302. A decent 460 could pull more gear, and still make some tire speed, or even spin the tires when in the deep stuff.
A rig equiped with lockers will be spinning all 4 wheels, and the weight of these turning masses will require more gear than one equiped with open diffs.
Lets not forget to throw in the weight of the vehicle. A fullsize long bed pick up will require more gear than the exact same vehicle with the same tire size, same trans, same t-case, and weighs 25% less.
General rules of thumb are a decent way to get close, but knowing and considering all of the variables will put you right on the money.
A 4 speed powered by a decent powerplant and 38" tall tires will be alright with 4.56's.
4.88's might be better for an auto, and the same size tires, or if you run heavy steel wheels with beadlocks, or heavy tires.
5:13's if you are a little low on power and have lockers with heavy wheels.
Different combo's will require a different set of gears, but you kind of get the idea.

I am one that believes that most undergear, and it is difficult to overgear a heavy rig.

 

Many good points Ed, rep to ya when i can...

 

https://www.ford-trucks.com/calculat...php/p-mph_rpm/
mph/rpm/ratio calculator

 

Tinian, here's where Ed and I disagree. His points are good for an offroad only truck, but since you said you want to drive on the street, then different rules apply.

Since an auto slips, then your rpms are up. However, the slipping can burn stuff up. You don't have an auto, so it doesn't matter.

I don't run big mud, but Ed does, so if you are looking at heavy duty mudding, then consider his points.

Here's my experience: I put in 4.10s with 33s and hated it. It revved too much on the street. 10 miles at 65 felt like forever. I switched 36s and never looked back. With the 4.10s and low range, I can do most anything I want, but still drive on the interstate reasonably comfortably.

I would measure your current tires, consider your level of happiness with your current gears, and look seriously at how much on/offroading you do. Also, do you live where you never hit over 55? 65? 70? If I lived in the mountains where all the roads were curvy and 55 was fast, then I would consider lower gearing.

We all have good points, but you need to consider them for your own personal application. I listened to people, and didn't like it.

 

I was hoping Ed would chime in on this thread. I didnt think about the tires not actually being the size they are. I think that might be why I feel im too low geared. My 38's aint really 38. I do feel like my truck would be perfect right now if I had an overdrive. Its great stop light to stop light but it sure seems like it wants to shift again real bad on the highway.

 

I do believe that Ted brings much to the table, and that was why I suggested that different combos and different applications all require a different ratio.
Many factors come into play, and I used a small 302 as just one example, but even this would be different if a 300 I6 was used. Imagine that the low end torque of a straight six would not tolerate turning higher rpms on the highway, so this sewing machine would sound and maybe even struggle to turn a constant 3000 rpm for extended periods of time.
A larger displacement engine, that is capable of such rpms might be right at home in this range.
I see Teds point, and understand (agree) with everything that he has to say. I beliieve the diffrences that we share are based upon engines combos, and the type of wheeling that we do.
He is a driver with finesse and asteady foot, while I am just a giant "run you over" monster that relies on wheel speed to manupulate obstacles.
I need a ratio that can get giant heavy tires rolling, and I rely on big power to keep them rolling.
It would not make sense to gear an engine to such a degree that it has to work out of its power / rpm band, but at the same time, the same is true for low end. Too low an rpm at cruise speed will greatly compromise the vehicles ability to accelerate, (especially a heavy truck) and too l ow an rpm might put the engine far too low in the power band. This would require a bunch of throttle input, and this in itself would be a compromise.

Sure would be nice if we could test drive gears huh?

 

My particular 300 seems to really like 2700 rpms. If I hit a hill and am doing faster, it will slow to that rpm. If I am going slower, it will accelerate to that. Based on this, with the 33s, I would slow down a lot, but the 36s fit it well.

I know it really isn't the same comparing my 33s-36s to Tinians 40s-44s, but the idea of figuring what works is the same.

Testing gears would be so cool Save some money too.

I just hate to see Tinian spend money only to be disappointed. That's what happened to me.

 

You know, we kind of cheat here. I have enough buddies that have similar trucks, and we can use a rear axle from another truck to see what a gear set up is like.
Fortunately I also have enough stuff in the stable to run a slightly different gear.
I do understand teds point of view, and agree in every way.
Gear selection is always a tough call. There is always that "what if factor".

 

Test driving sure would be nice... too bad huh?
I was also thinking ahead of the game, thinking I'll upgrade to a larger tire than the 40's right now. Maybe 5.13's are too much, which is exactly why I posted here before going and wasting more money.
I have a mild built 360 powerplant, its no 460, but also no 302 like mentioned earlier.... but a motor swap isnt out of the question either. (Ive got so many project I want to do with this truck right now it drives me crazy somethimes...lol).

So maybe a happy medium at the 4.88's?
Most of my driving here varies between backroads going no more than 40, and highway at about 60.

 

what kind of wheeling and tires are you gunna do/run