Changing from 3.73 to 4.10 gears

[oakmandan]

Hello all,
After towing our new Reflection 320MKS from Eastern Iowa to Estes Park Colorado and back, I need more power for the hills. I have a 2015 F-250 with the 6.2 Liter engine. I have 3.73 years. Can they be swapped out for 4.10 gears, and will it help ?
Thanks

[RCMAN46]

"If the same truck is expected to pull 35000 lbs down that same highway it can be determined that 440 HP can only pull the hill at about 52 mph. It would be desirable for the transmission to again be in 4th gear while the engine is running near 2800 rpm.

This truck will have a little smaller diameter tires and should have a 4.30 rear gear ratio."

Ok but lets assume I have enough horsepower go 60 mph or the hill is a little less grade. Then a 3.73 gear would be best at 2800 rpm and 4th gear.

[Turtle_n_Peeps]

4x4ord wrote:

Turtle n Peeps wrote:

noteven wrote:
Anyone know why pickup OEM’s give higher trailer weight ratings with a spec change to lower rear axle ratio only?

It's about duty cycle. The more gear a truck, tractor or motorcycle has the more duty cycle it has.

My tractor has a gear into a gear into a gear. Wide open in low it will go an amazing 1/2 MPH but it puts down tens of thousands of ft/lbs to the ground.

The formula is this for 1 horse power: Lifting 33,000 lbs one foot in one minute. Now a horse can't lift 33,000 lbs without "help." So if the help comes in the form of gears or block and tackle or anything that will "help" the horse lift lets say 500 lbs 66 feet in one minute. (I think I did the math right on that?) :R

It doesn't matter if that horse can lift 33,000 lbs one foot in a minute or if that same horse lifts 500 lbs in 66 feet in a minute or any other combination..............that horse is still putting out 1 horse power.

That is all a gear is doing with a tow rig or my race car or whatever...........it's still putting out the exact same HP to the ground........same as the horse example above.

So part of the reason OEMs give higher trailer ratings to truck's with lower speed gear ratios is, as T and P points out, the torque multiplication to get the load moving but I believe an even more important aspect of specing the right gear ratio is to start with an assumption of how the truck will be used including the weight of the load, the grades to be climbed and the power available. Say a 25,000 lb diesel truck/trailer with a 440 HP engine is being speced to pull an RV down highways with 6% grades and 70 mph speed limits. It can be determined that 440 is capable of moving a 25000 lb load along at 65 mph going up a 6% grade. The ideal gear ratio for this application would cause the transmission to shift into direct or closest gear available to direct (4th) and allow the engine to run close to the rpm where maximum power is available (2800 rpm). The 3.55 ratio in my truck puts me at 69 mph at 2800 rpm.

If the same truck is expected to pull 35000 lbs down that same highway it can be determined that 440 HP can only pull the hill at about 52 mph. It would be desirable for the transmission to again be in 4th gear while the engine is running near 2800 rpm.

This truck will have a little smaller diameter tires and should have a 4.30 rear gear ratio.

^^^^ Yep! Just like my horse example above, big trucks get more gear because they will haul very heavy loads and need the gear to "lift the load" just like the horse. That horse is still just "one horse power" but the gears or block and tackle give that 1 horse power the ability to lift 33,000 lbs at the expense of time OR distance.

When it's at the expense of time OR distance power will remain the same.

[thomasmnile]

Turtle n Peeps wrote:


That is all a gear is doing with a tow rig or my race car or whatever...........it's still putting out the exact same HP to the ground........same as the horse example above.

But without leaving a trail of road apples! Sorry, couldn't help myself..:B

[4x4ord]

Turtle n Peeps wrote:

noteven wrote:
Anyone know why pickup OEM’s give higher trailer weight ratings with a spec change to lower rear axle ratio only?

It's about duty cycle. The more gear a truck, tractor or motorcycle has the more duty cycle it has.

My tractor has a gear into a gear into a gear. Wide open in low it will go an amazing 1/2 MPH but it puts down tens of thousands of ft/lbs to the ground.

The formula is this for 1 horse power: Lifting 33,000 lbs one foot in one minute. Now a horse can't lift 33,000 lbs without "help." So if the help comes in the form of gears or block and tackle or anything that will "help" the horse lift lets say 500 lbs 66 feet in one minute. (I think I did the math right on that?) :R

It doesn't matter if that horse can lift 33,000 lbs one foot in a minute or if that same horse lifts 500 lbs in 66 feet in a minute or any other combination..............that horse is still putting out 1 horse power.

That is all a gear is doing with a tow rig or my race car or whatever...........it's still putting out the exact same HP to the ground........same as the horse example above.

So part of the reason OEMs give higher trailer ratings to truck's with lower speed gear ratios is, as T and P points out, the torque multiplication to get the load moving but I believe an even more important aspect of specing the right gear ratio is to start with an assumption of how the truck will be used including the weight of the load, the grades to be climbed and the power available. Say a 25,000 lb diesel truck/trailer with a 440 HP engine is being speced to pull an RV down highways with 6% grades and 70 mph speed limits. It can be determined that 440 is capable of moving a 25000 lb load along at 65 mph going up a 6% grade. The ideal gear ratio for this application would cause the transmission to shift into direct or closest gear available to direct (4th) and allow the engine to run close to the rpm where maximum power is available (2800 rpm). The 3.55 ratio in my truck puts me at 69 mph at 2800 rpm.

If the same truck is expected to pull 35000 lbs down that same highway it can be determined that 440 HP can only pull the hill at about 52 mph. It would be desirable for the transmission to again be in 4th gear while the engine is running near 2800 rpm.

This truck will have a little smaller diameter tires and should have a 4.30 rear gear ratio.

[Turtle_n_Peeps]

noteven wrote:
Anyone know why pickup OEM’s give higher trailer weight ratings with a spec change to lower rear axle ratio only?

It's about duty cycle. The more gear a truck, tractor or motorcycle has the more duty cycle it has.

My tractor has a gear into a gear into a gear. Wide open in low it will go an amazing 1/2 MPH but it puts down tens of thousands of ft/lbs to the ground.

The formula is this for 1 horse power: Lifting 33,000 lbs one foot in one minute. Now a horse can't lift 33,000 lbs without "help." So if the help comes in the form of gears or block and tackle or anything that will "help" the horse lift lets say 500 lbs 66 feet in one minute. (I think I did the math right on that?) :R

It doesn't matter if that horse can lift 33,000 lbs one foot in a minute or if that same horse lifts 500 lbs in 66 feet in a minute or any other combination..............that horse is still putting out 1 horse power.

That is all a gear is doing with a tow rig or my race car or whatever...........it's still putting out the exact same HP to the ground........same as the horse example above.

[rhagfo]

Well part of the issue is final destination is Estes Park Colorado about 7,500' a NA gas engine will be loosing a fair amount power at that elevation.

[4x4ord]

If you're having trouble getting rolling in 1st gear lower gears help but once rolling it makes little difference. Lower gears are not better if you don't need them.

[noteven]

goducks10 wrote:

noteven wrote:
Anyone know why pickup OEM’s give higher trailer weight ratings with a spec change to lower rear axle ratio only?

Lower gears (4.10-4.30) put less stress on the running gear.
Try towing the same load with 3.42 as 4.10 and you can feel the truck straining just to get it moving.

.... but...but....people always post “your transmission gears will look after the gearing you need....and no lower rear ratio will improve towing performance...” don’t the OEM’s know this? 🙂

[4x4ord]

rhagfo wrote:

4x4ord wrote:


To pull your 20500 lb unit up a 7% grade at a steady 55 mph would require very close to 290 rear wheel horsepower. (Exactly 210 HP to raise the load up the elevation gain plus another roughly 80 HP to overcome wind and rolling resistance) That means something like 342 engine horsepower. So long as the vehicle is geared appropriately it makes no difference whether that 342 HP is being generated by a diesel engine running at 2500 rpm, a gasoline engine running 4500 rpm or an electric motor running 1750.


Edit: I corrected a calculation error but even if your truck is capable of putting 85% of its engine's power to the pavement it would only be capable of 50 mph pulling 20500 lb gcvw up a 7% grade... and this assumes only 65 hp is being used to overcome wind and rolling resistance. I'm thinking the hill you've measured your speed on is not marked accurately or is not a constant 7% grade.

I forgot to mention that at the base of this climb is a 45 mph corner that is truly 45 mph when towing so I also accelerated to 55 while going up this grade.

At 2500 rpm your engine is only capable of about 90% of its peak HP which comes in at 2900 rpm. So either your engine is capable of making very close to 380 peak HP or that grade is not 7%.

I'll bet if you check the elevation gain between the bottom of the hill and top on this map and measure the distance along the road from the same two points in Google maps you'll find the hill is more like a 5 or maybe 5.5% grade.

https://www.freemaptools.com/elevation-finder.htm

[goducks10]

noteven wrote:
Anyone know why pickup OEM’s give higher trailer weight ratings with a spec change to lower rear axle ratio only?

Lower gears (4.10-4.30) put less stress on the running gear.
Try towing the same load with 3.42 as 4.10 and you can feel the truck straining just to get it moving.

[noteven]

Anyone know why pickup OEM’s give higher trailer weight ratings with a spec change to lower rear axle ratio only?

[RCMAN46]

Here is a calculator that the OP can use.

Engine RPM calculator

Notice there is no hp or torque in the calculator.

Just determine what RPM and speed you are comfortable with or the RPM where your engine makes the most HP and have at it with axle ratios and the transmission you have.

[mkirsch]

What's saying you MUST stay in that gear?

As long as you aren't in 1st, you can always drop down another gear to accelerate. If you're running out of power in 1st, you probably shouldn't be where you are, OR you've got serious mechanical problems.

In the case of the OP, where he's locking out 6th AND 5th for a majority of the trip, I agree, a gear change is a good idea, and I agree, 4.30 or nothing.

[Huntindog]

The people with their charts attempting to show that just dropping a gear in the tranny will do the same job are ASSUMING that they will be able to stay in that gear at that speed all the way to the top of the mountain.

In the world that I tow in, there is almost always something that prevents this.... Usually two semis side by side drag racing up the hill at 5-15 MPH. If you have lower rear end gears, you will be able to regain speed much better after slowing for whatever reason.
The world isn't always flat, and traffic doesn't always cooperate either.

As I keep saying, drive identical trucks with each gearset.... Then judge for yourself.

A chart or math calculation won't produce in the real world like it does on paper, or the computer screen.

[wnjj]

Turtle n Peeps wrote:
Ben, here is where I'm at. These guys say it much better than I can in limited time.

Here is a calculator you can play with.

As Thomas Andrews would say: "tiz a mathmatical certainty."

If you play with this calculator for awhile you will know if you have an engine that makes 1000 ft/lbs at 1000 RPM you "will" make 190.4 HP. "Tiz a mathmatical certainty." If you jump the RPM to 2000 and keep the torque at 1000 ft/lbs tiz a mathmatical certainty you will get 380.8 HP.

I "know" 5252 is the point that torque and HP will cross on a chart. "tiz a mathmatical certainty."

All the above are mathmatical certaities just as one will never make power (read HP) with gears.

You cannot make HP with gears, but since your engine does not have a flat HP curve you can certainly affect the amount the HP your engine is producing at the time by using gears to change the RPM it runs at for a given load & road speed.