I am probably the only guy on this board that does not understand this.

What impact will different rear axle ratios have on a pick up.

I am about to buy a new one and can get 3.08 or 3.42 rear end ratio.

Thanks

In Minnie Soda, I'd go 3.42, in Tx. 3.08.

Lower # less rpm's per given miles per hour.

and just to be clear, higher # is better towing and acceleration

ked

I would go 3.42 regardless of were you live.Everything has overdrive nowdays.It all boils down to how many times the driveshaft has to turn to turn the tires once.a 4.11 means the shaft turns a little over 4 times to turn the tires once,and a 3.07 means the shaft only needs to turn a little over 3 times..The higher the munber of your gear ratio the lower geared you actually are .Low gears give more power,and higher gears give you reduced rpm..

I just notice were you live .I would try and get a limited slip rear differential .

What's the rest of the info on the truck (make/model/engine)? Do you plan to tow? If yes, what?

Well I am in Texas, and have a 3.73. Good for pulling power, but a bit taller than I really need. Ford sells them with 3.55's and I wish I had held out for that ratio. The engines revs at a given speed are proportionately less.

3.55 is what i like.

3,55 is good for a street rod also.

I think both our '14 F150's are 3.55, both are 5.0.

The 3.42 ratio will have your engine turning more rpm's at a given speed than the 3.08 ratio will. For example, say at 60 mph in top gear your engine is turning 2200 rpm's with the 3.42 ratio, it would run at 2000 or so with the 3.08 gears. This means that the 3.42 gears would pull a little better when towing since the higher rpm's put you more into the engine's power band. The downside is that it'll likely give you a little less fuel economy than the 3.08's.

If you're planning on putting bigger tires on the truck then you want the 3.42 gears since going to a bigger tire effectively reduces the gearing. To get an informed answer we need to know what truck, engine, and transmission you're talking about though. Everything's a compromise with gearing and what's good for one combination isn't good for another. The final drive ratio of the transmission matters as much as the rear end gearing.

As one poster said, always get the limited slip or e-locker type rear end, don't buy a truck without that.

My old super duty 250 with 5.4 has the 4.11s with 5 speed,and I run it 75,and 80 on the interstate..My Ranger has 3.73s and I wish it had a lower gear because it only has a 3.0,they do both have the limited slips though.

Definitely 3.42, especially if you need to haul anything. Bigger number means higher rpm's and more pulling power. You "might" get better mileage with 3.08s but with overdrive transmissions you'll probably downshift on the slightest of hills negating any gain.

What the number means is the number of revolutions the drive shaft will make for each revolution of the axle. There are a limited number of ratios because of how the gears mesh, 3.08, 3.55, 3.73, etc. The higher the number, the faster the driveshaft has to turn and the lower the gearing.
Since the driveshaft, hence the engine, turn faster at the lower ratios, you get more power but less fuel mileage and road speed for a given engine speed.

I appreciate all the comments

Other info-
It will be a Chev Silverado
5.3L engine
4WD
I don't tow anything
Use will be highway and hunting
The hunting will be off road but nothing extreme, farm fields etc

Don't get the 3:08 gears.

If you have need for a 4x4, then you wouldn't be satisfied with the 3:08 gearing.

3:42 is a happy medium.

I disagree, with a transfer case and low range 3.08 will be fine especially if your not towing anything. Been there had 2, a Blazer and a K1500 with 2.73 rears and 305 V8 and had no issues off road in Maine with either. YMMV

[bleep] i drove my dodge dart around with 4.88s but it would turn 8 grand no problem.

running a 28 inch tall tire.

I have run pickups with gears ranging from 2.72 to 5.42. With today's overdrive transmissions, I will never own another truck with taller gears than a 4.10. But I use a truck for hauling and towing, sometimes up to a combined gross weight approaching 20,000 lbs.

If a guy never throws more than a ton in the back of his pickup, and never pulls a heavy trailer, he could get along quite well with today's high output engines and a five or six speed tranny combined with 3.08 gears.

Just shift it into low range when you leave the road.

Run 3.55 in my dodge v8 4x4 w/low range and with the over drive it is a great highway cruiser. I do a lot of off-road driving in the Sierra's and would like the 3.90 option next time.

Can't help as I have 4.10's in my and my wife's trucks - both used to haul and tow - also get around some "interesting" country where there aren't even 2-tracks.

i can set up rear ends have all the tools to do it plus a jig to narrow danas 60s and chysler 8 3/4s

If you do much off road you will never regret the 3.42. Something around 3.50:1 is a good general use ratio. Bigger # for more pulling power, bigger tires, off road. Smaller for fuel mileage or higher top end, both of those is often theory, as someone posted you can end up not using overdrive or shifting all the time.

In real simple terms, if you are most interested in gas mileage, get the higher gear (lower number), if you are more interested in performance, get the lower gear (higher number).

You can't compare gear ratios from one truck to another if they use a different motor, transmission, or different size tires. All the different gear ratios mentioned in this thread mean nothing to the truck you are looking at unless they are talking about the exact same motor, transmission, and tires.

if you run a lift with taller tires go with 4.11s

Different sized tires????????

I did not know they made anything but 255-85-16. Doesn't everybody run those?

Since the truck in question is 4WD switching the ratio on the rear will require switching the front axle too.

yes it will

I'm pretty sure new trucks come with the same gears front and back no matter which ratio you want.

it depends if there running the same axle front and back

fords use to run a dana 44 up front and a 60 in the back

but im old so things might of changed.

While there's a lot of good information and advice here, I would agree with Idaho Shooter...with the caveat that you do indeed have a 5 or 6 speed tranny and you don't plan on towing. I had a GMC with a 5.3 and although it's a good overall engine, I found it rather anemic. That said, even the Lower ratio (3:42?) is not all that low-geared so I don't think you'll get hurt either way.

Go 3:42. If you can afford a new truck, you can afford the small gas mileage penalty to have a truck that is not a turd off the line or when crawling/accelerating/towing.

3.55

my dually has a 70 in back and a 60 up front.

A pickup might use different models of axles front and back but they still have to have the same gear ratios or you will destroy the transfer case.

no you are wrong.

He's buying a new truck. Gear ratio is an option he is considering. It's going to have the same gears front and back regardless of which he chooses. Trust me.

The ratio front and rear had better be damn close or you'll be wrecking parts in short order. Ford used to use 4.11s front and 4.10s rear and maybe 3.50 and 3.55s but really close. If you don't believe me put different sized tires front and rear and lock her into 4x4. Now go try to turn around in a circle and listen to the pops and pings.

To the OP, I'd get the 3.42 ratio on principle just because it's a pickup and you may want to tow or haul something. And it's not like they will be low enough to really have your RPMs up even at highway speeds. I prefer 3.73s for all around 4x4 pickup use but you will probably do fine with whatever you chose.

this is what i remember and tire size plays into it, but like i said its been yrs since we were building differentials,

Not an expert but thats the way I thought it worked also? Otherwise you would get "wind-up" and potentially tire wear problems as the front and rear axles would be turning at different speeds?

Anybody else see the humor in this thread? It's just like almost every other thread here. A guy asks a very specific question about a specific truck he is wanting to buy. I'll bet over half the posters in this thread never even read the original post. Was the fact that a 4WD has the same gears front and back ever in question? Does anyone think you have to specify what gears you want in the front AND back when buying a new truck? Or what axle it has front or back? Or recommending a gear ratio that the truck doesn't even come in with out even knowing any of the actual factors that go into choosing a gear ratio.

Lot like a guy asking about his 7X57 and being told he needs a 30-06 and then debating whether that 30-06 needs 165 or 180gr bullets.

will then every thread would be boring, and front and rear are not always the same.

find an online gear ratio calculator. you'll need to input the tire size and which transmission/transfer case you'll have.

much will depend on the first gear ratio of the transmission but the low range gear ratio in the transfer case will matter somewhat too.

long story short, with a tall overdrive and lousy first gear found in many trucks today, I would get 3.42 of those two, more so if you plan on going to a larger tire down the road. my Suburban came with 3.73s but when I swapped in one ton axles, I installed 4.10 gears to accommodate 33" tires. even with the transfer case in low range (NP 241 with 2.72:1 low range), it seldom gets out of low/low off road.

Dale06,
Think of it this way: say you are buying a bike. All things being exactly equal (same exact bike, just different gearing on each bike), the 3.08 is say like a bike always stuck in 10th gear. The 3.42 is like the other bike being stuck in say 5th gear. The 10th gear scenario will be slow from stop lights, harder to get moving, and your legs will work harder when you carry any weight (say a backpack in this scenario), or go up hills. But you will be fast and efficient going down the highway when it is flat. The 3.42 or 5th gear scenario would be faster out of stop lights, easier when lugging that backpack, better for hills, but it isn't as good on the open highway as you will be peddling you arse off trying to go the same speed as you did on the 3.08 scenario.

And there is the explanation of your choices.

There is no reason to get the 3.08. The 3.42 will give you more power whether you need it or not, and most likely no loss of fuel mileage. The only reason truck companies even offer those higher gears is because they can show about 1 MPG better for CAFE standards.

Strictly on interstate driving, on level ground you might actually see a faction of 1 mpg better with the 3.08. In normal driving the 3.42 will be about the same and maybe better. While the 3.08 theoretically means lower RPM, it also means the transmission will be operating in the lower gears more. Net result is about the same.

An extra high ratio, like the 3.08, can often cost you mileage, not gain it. In town, or any slower traffic, you have to run in lower gears which cut the mileage plus if you have any load, hills, or wind you'll be shifting down.

I own basically the same truck, i get 20 highway with 3.42s i dont see anyone talking about the 6spd trans these trucks have, at 80pmh im right around 2000rpm on the highway.

Dad had a 90 f150 300 six, 5speed, 4WD 3.07 rears. Gutless wonder . Bought a new 95 everything the same but with 3.55 rears. Huge difference in driveability performance and better fuel mileage. It just worked better and could now be driven in the local hills, in overdrive, without flat footing it just to go up a hill. Newer trucks have more gears but that does not change anything unless you know the ratios. Then if you have two OD's you will want the 3.42

In pickups they are, or extremely close, because pickups are equipped with the same size tires front and back. Sometimes the rear axle is very slightly shorter geared because the rear end has less distance to travel when rounding a corner. But it is very slight.

Farm tractors or ATV's on the other hand might well be equipped with different axle ratios to accommodate different rolling diameter on front and rear tires.

Even if the pickup has a dana 44 in the front and a 60 in the back (like my 75 Dodge W2500) with different size ring gears. The gear ratios will be the same.

You're just taking the fun out of it now.