Just wanted to share my recent experiance on gears. About 2 years ago I upsized my tires to 35's, nothing unusual. And left the gears alone with 3.73's. It was after that when I bought my 28ft toy hauler made of lead and stone I think. Point being I never had the chance to tow it with stock tires. I pretty much got used to the heavy load on all the local hills. Well I took it with me to Oklahoma, and that was just brutal. Could not hold any speed on any hills. Always kicked off the cruise control and was just working really hard in general. It could climb the hill fine, but I actually had to drive the truck as opposed to along for the ride. So when in Tuttle, I decided it was time to change the gears, ordered up a set of 4.56's from Randy's R&P(Awesome Place!) and did an on the spot change. WOW!! HUGE improvement in towing and engine load. Most hills were now done in overdrive, the truck was obviously happier, and my mileage went up by about 3 mpg. If I were to do it again, I would probably go with 4.30's. As it is I do 70 right around 2400rpm.

All I can say is if you haul anything up a hill larger than a mole hill, and are on the fence, then do it. Really brings back the concept of letting torque do the work, and not horsepower.

 

Moving to Colorado convinced me in a hurry to swap in a new set of gears. So glad I did it now.

 

couldnt agree more best mod i ever done was the 430 gears.

 

Thanks for the input! I would love to swap gears to run my 35's. I really seem to notice more and more the effects of larger meats.

What ratio do 4.56's give you w/ 35's? How about 4.30's? Care to say what a gear swap costs?

 

fn74, did you install lockers or anything like that? i have a front axle seal leak sooo i am thinking about a gear swap and lockers. also in about 20,000 more miles i will be installing 35's.

 

Yeah, now that Im runnin 38 inchers I really need to change my gear ratio. Im not sure what to go with though...here in about 3 months I will most likely be running 40's. Any suggestions?

 

Exactly, proper gearing is proper gearing. I swapped in 4.30s with my 35s and it helped so much here in hilly california. With this setup my overall gearing is around 3.90.

 

i have an 88 F150 2wd and am also thinking about gears, how much does it cost and how long does it take to install? im just tryin to get a lil torque boost as i am in the process of lifting 4 inches with 35 inch all terrains or mud tires

 

Lower gears resulted in improved MPG? That doesn't make sense to me. Not saying it didn't happen, just doesn't make sense.

 

It would make sense if he was working the engine really hard all the time and switching gears lightened the load. Maybe not that much, but I could see it happening.

 

Unlike swapping gears on a small displacement gasser, the immense torque of a diesel does not make big tires undriveable at all, but you still lose a lot of performance, increase drivetrain and engine loads, and usually lose fuel economy. So most Duper Duty's come with 235/65/16 tires, or which equates to a 31.7" tall tire. Wheel sizes change through the years, but the overall tire height is close to the same.

So if you started with 3.73 and went to a 35" tire, your effective gear ratio just went from a 3.73 to about a 3.37!!. Now change that to a 4.56 with the 35's and your effective ratio is now 4.13, or basically a 4.10. 4.30's would give you an effective ratio of 3.89, so almost close to stock. The choice between the two depends on a few things. Future tire size and use of truck.
If you think you might do 37's then go with the 4.56's without a doubt. If you plan to tow heavy loads close to the trucks limit with 35's then do the 4.56's. otherwise you will lose MPG in a unloaded daily driver. I do a lot of towing of my lead brick for a camp trailer so opted for the lower gears, which is almost equivalent to having 4.10's from the factory. A gear Swap should not cost you more than 350 per end for labor. Closer to 250 for the rear. Right now I noticed that Randy's is having a 4wd special.

 

For the most part lockers are not a viable daily driver application unless you go with an ARB air locker. I chose to go with a Detroit True Trac that is a clutchless limited slip and strong as they come. It has been a perfect setup for my use of daily driving and occasional offraod. They do not make them for the Dana 50, but do for the 60 in the front.

For you to get back close to the stock 3.73 final ratio you will need 4.88's. If you tow then the next step lower.

Depends on what kind of mileage you want. Us with the diesels have ample torque and do not need to go lower than stock. However on the Gassers, going a few ratios lower than sotck can net some major off the line response at the expense of fuel mileage. At the minimum you should go with 4.10's, and for the most bang for your buck, 4.88's will net you some head snapping off the line acceleration. If you plan on some engine mods, then go with the 4.56's. If fuel economy is key and you do not tow, then 4.10's will prove useable. Keep in mind, I am speaking on a combination of Mustang and recent truck experiance, not actual results. However i feel the info I gave you is a solid educated guess.

Unloaded, sure I would also say I am full of wood shavings. However under a heavy load is an entirely different scenario. Lower RPM does not always mean better fuel economy, otherwise cars would come from the facory with a final drive ratio that put them at idle. It is all about engine load. There are a lot of other variables such as BSFC, Peak torque, speed and so on. With my 3.73's and tall tires, the engine was under heavy load all the time. It took longer to get to speed, and required more throttle to hold the speed and to do hills. Think of it this way. Every ride a good ol 10 speed bike? Ever go up a hill? Chances are you shifted down to increase the torque to the tires and to make the load lighter at the pedal, and on the chain(transmission). Even though your legs were going faster, it was easier work requireing less overall power and energy to maintain the same speed or close.

The higher gearing better mileage comes into play going down hill on that same bike. Your weight just got lighter(thank you gravity) and now your leags are pumping about as fast as they can go. You are now fighting your own limits, and burning a whole lot of energy to pedal as fast as you can. Shift up to 10th gear and you are now back in your comfort zone again.

So long story short, my unloaded freeway trips at the same speed will suffer from the motor spinning faster unloaded. However under load, my mileage will increase due to the gears allowing the motor to "pedal" easier. That is why transmissions keep coming out with more and more gears. It is all about keeping the motor at it's peak, be it for torque or for fuel efficiency.

 

Awesome FN74 Thanks for the advice. I was also looking at this site: http://www.4wheelparts.com/gear_ratio.html

According to this chart, im looking for a 5.29 or 5.38 ratio. Is this even possible?

 

Thanks for your help, Jason!

 

By looking at that chart, the RPM doesn't change as much as I thought it would with a gear swap. Makes me actually think about changing my gearing. Great, another thing to add to the list.