11screw50

The ratio in the transmission absolutely does have an effect on pulling power at the wheels. The combination of transmission gear and rear end gear determines the multiplier. Why do you think downshifting helps when going up hills? It isn't just because it pushes you to a higher RPM, it is also because 5th is a different ratio than 6th and therefore provides a different multiplier. Your rear end gears have not changed and yet by shifting you've changed the pulling power at the wheels.

As for why not use the transmission to handle gearing and have a 1:1 in the rear end, it would make transmissions bigger. So you handle part of the gearing at the rear end and the rest in the transmission.

Dirttracker18

Why in the world would you think the transmission would need to be bigger. It would only be a matter of different gears, not larger or more. The point to deeper gears is to reduce the need for downshifting by keeping the engine in a more optimal RPM range. Vehicle gearing is designed for normal weight loads. An upgrade will be better under heavier loads but cost fuel mileage under normal loads.

It's clear your understanding is based on opinion and not fact so this discussion is going no where.

Suffice it to say, rear gear does make a difference in towing. Simply stating you believe it does not does not change the fact that it does. Nor does it negate the math that proves otherwise.

A chassis dyno can show the effect that a gear change makes by seeing the change in torque with different gears.

Velosprout

The purpose of the transmission is to convert the speeds of the engine at 700 to 5000 revolutions per minute into a useable speed that can be applied to the transfer case and driveshafts that can be used in all trucks; from all-highway commuters, meter-reader trucks, grocery-getters to heavy-towing camping trailer trucks, heavily laden landscape contractor trucks, and hard-worked farm pickups.


The purpose of the differential gearing is to convert the rotation of the driveshaft to the axles in a manner that is best suited for that individual truck's purpose. The harder-working, towing, payload-bearing trucks will last longer and be less strained with the 3.73 gears, but spend more gasoline in the process.


It's best to do the research and buy more truck you need initially than to be later plotting upgrades and modifications to try to increase capabilities. Even if you don't need it now, having excess towing/hauling/payload capacity allows for you to consider other uses in the future and have more potential buyers of your used truck in the future.

parcours

Good discussion...

I was not aware that Ford used 9.75, I thought they were all 8.8.

I have a 2012, FX4, 5.0. I just ordered a set of Lubelocker gaskets for an 8.8.

How can i make sure which axle I have?

Kenferg1

You are kidding me, right? I do know what I'm talking about. You can absolutely run a 1:1 differential ratio and still have the ability to tow. You simply have to build a transmission (as was noted by another poster) with enough gears to translate the torque from the engine to the wheels. The ratio in the differential simply allows for a smaller transmission with fewer gears by using mechanical advantage at in the differential. This, sir, is basic physics.

The lock-out feature has nothing to do with locking out the torque converter (preventing lock-up). It simply reprograms the transmission to keep it from going into the next higher gear(s). The torque converter can and does still lock up. If the torque demand increases beyond the programming specifications for lock-up, then the transmission decouples and reverts to the fluid coupling in the torque converter. Locking out the gears in the transmission has no effect on this. Tow/Haul mode does have an effect on lock-up, but it does not lock-out the transmission unless the program recognizes the torque demand and simply keeps it in the appropriate gear for the power that is demanded.

That is why it is my opinion, based on math and physics, that for most people who do not tow heavy on a regular basis a more fuel efficient axle ratio may be appropriate. Utilizing Tow/Haul and the transmission lock-out feature will allow them to tow most of the loads.

I have had two f150s with the 3.5 Eco. The first one, a 2011, had 3.31 open diff. My current one, 2014, has 3.73 E-locker. In daily driving my MPG is virtually the same (within 1 mpg) On the interstate at 70 mph it differs by about 2 mpg. While towing (the same travel trailer with both, about 6,000 lbs loaded), they both towed fine. There were times I had to lock out 6th gear when traveling out west with the 2011 (3.31), but there was never a problem. I walked any V8 gasser climbing out of Denver. In fact, I had to watch my speed because I could very easily have towed 75mph in 4th gear. The 2014 (3.73) tows a little better since it will hold 6th gear a little longer. But on a day to day basis, there is virtually no difference.

In the end, this is America. Get what you WANT! If it makes you feel better to have the 3.73 gears, then get them. If you want 3.31, then get them. If you want a monkey riding a tricycle, well that's fine too. But, please do brush up on your facts before you call out someone for being wrong. Otherwise, you look like an ***.

Dirttracker18

We are talking about two different features when it comes to lock-out, we are both correct in regards to the definition.

I never said the truck with lower numeric gears will not tow the load, the discussion is whether or not higher numeric gears are better for towing. Please do not put words in my mouth.

You, on the other hand stated, and I quote "As to the rear end ratio argument, I would say it's kind of pointless."

I was attempting to show you and others that it is not pointless. There is a difference and it is significant.

Next, I do know what I am talking about as I was a trained mechanic in my former life before changing careers. I have also spent 20 years building, maintaining and driving race cars in 4 different divisions. I have an excellent understanding of transmissions and their gearing as well as differentials and the advantages of different ratios.
Have you ever had a transmission apart?
Have you ever had a differential apart? I am not talking about removing the cover or changing the oil.
Do you have any formal training in automotive repair or engineering?

I speak from not only experience but training. I am not some know-it-all internet troll speaking out of his ***. There are many on here that I learn from all the time. There are other times that I attempt to help others learn and understand.

So if you want to stick to one discussion I am more than willing to debate ideas. However you went from stating that rear gear choice or difference is pointless to it's all choice and any gear will tow. Then you talk about gear differences making no difference day to day which it would do little in day to day driving.

I agree with your second statement, any of the gear choices will work for towing. However, there is no doubt that for towing any significant weight, deeper or higher numerical gears will be functionally better. There is no debate to have hear and this is the point I was trying to make.

With further regard to your trucks, both are eco boost trucks with very high torque numbers and great torque curves. They need less gear to perform the same function as a normally aspirated engine. You even note yourself that that better geared truck needed less downshifting. That in and of itself proves my point.

Finally, my truck's gears do not make me "feel" better. My trucks gears allow me to tow my heavy loads easier with less effect on the rest of the drivetrain. As you noted yourself with the difference in your two trucks.

Obviously if you had no plans to tow or haul heavy loads (relative to the truck) then less gearing would be a better choice.

Kenferg1

Now, let's get the record straight. You replied, and I quote, "Sorry but you are completely wrong here.

if this is the case why would engineers bother to have different gear ratios?

Why not set up the trans to accommodate gearing and have a 1:1 gear in the rear?

The trans does not have the same effect as the rear ratio. In the trans you run through gears to get to the speed you want and stay within reasonable RPM while doing it."

You posited as question about different gear ratios. I simply explained how that worked. You then posited about a 1:1 gear ratio in the rear differential. Again, I explained it. You then stated that the trans does not have the same effect as the rear ratio. I think there are engineers that design, develop, and test big rig transmissions that would destroy your assumption. This discussion was not about that though. The discussion was about the difference. I stated my opinion based on facts and experience.

Smokeywren made the best statement, "That 5% difference in gear ratio will make a 5% difference in engine RPM at the same road speed. And depending on the HP and torque curves of your engine, that difference in engine RPM could make a difference in pulling power." This is something that I fully understand, having used sprocket changes on motorcycles to adjust the torque multiplication on my bikes to best utilize torque. The rear end ratio is the cheapest thing to change in order to achieve the best use of torque and horsepower curves of a given engine. You see this in auto racing all the time. Transmissions are complicated and expensive; rear end gear sets not so much.

The original poster noted that he would probably not pull the max load. So I offered an opinion based on facts and my experience with two different axle ratios.

I appreciate that you clarified what you meant by lock-out and lock-up. Those were probably interchangeable, but recent automatic transmission developments have led to two distinctly different definitions.

As to your experience, I defer. I have not disassembled or rebuilt a transmission or an engine. But that does not disqualify me from understanding the fundamental principles of powertrain systems. I will maintain my opinion, that for most people - and the OP sounds like he uses his truck the same way - the big argument over rear end ratios is overblown, and with the proper use of the gear ratios in the transmission, most loads will move fine. Of course, this changes if you have special circumstances, but if you are going to tow at or near maximum capacity, then you really need to move up in truck size.

BTW, the photographs at the website (I assume it's a friend's or your wife's) are excellent. It's not easy to get good pictures of children.

Dirttracker18

To clarify, the transmissions job is to keep the engine within a specific RPM range for a given speed while the rear gear is to provide the correct gearing for the purpose of the vehicle.

The idea of using the transmission is not unheard of as this is the idea in the transaxle of a FWD vehicle which performs both functions within one device. Although, even in that instance a gear set is still utilized after the transmission.

As to your note about big rigs, keep in mind their rear gears are not 1:1 and they use both the trans and rears as I explained. As for their size (is that what you are referring too?) that is accommodate the large number of gears. Their trans still performs the same function, keeping that limited RPM diesel in the correct RPM range to maximize the torque curve. They still employ a gear set in the rear to optimize pulling power.

All I want to do is dispel the myth that rear gear is not important when considering towing. It is an important consideration.

On a totally separate note, my wife is the photographer and couldn't be more proud of her. She has found a great way to display her artistic talent and is able to combine that into a way to make a living. I wish I could say the same for my racing career which cost far more than I ever made.

Boulevard

Its the wonder of the calculator once again and people quoting engineers that they have never met nor never will be.

5% means...absolutely nothing unless you apply it to an RPM. 5% at 4000 rpm is not the same as 5% at 3000 rpm, they are vastly different because the torque/hp curves slope up quite drastically as engine RPM climbs. In my truck, at the RPMs that I tow, a 5% change in gear ratio means a difference of about 25ft/lbs torque and you are telling me that this small difference is critical when driving a 12,000lb truck/trailer at highway speeds. Look at it this way, there may be a difference of about 5% in the gear ratio but at my RPMs it means that there is only a difference in torque of about 3.5% at the engine because of where I am in the torque curve. 3.5%...think about it. That is like telling a person that if they go from 265/55r20 to 256/60r20 that they have to drop their towing capacity by 1700lbs.

Go back to your calculator and stop misquoting engineers that you have never met.

11screw50

OK, your posts makes ZERO sense. You say that you have 25 ft-lb less torque at the rpm you tow, then you say that is only 3.5% difference at your rpm.

As for my calculator, I prefer the $10 Casio that I have sitting on my desk at work.

And I generally do not quote myself (even though I have met myself)...