4:10 or 3:73 ?

TxGearhead wrote:
I'm borderline payload, rated 4018#, with my cabover. I know how 5th wheel pin weights are fudged by the Rv manufactures. I'm looking at Alpines with advertised pins of 2400-2600. I'm thinking that will realistically be 3500+ after the W/D and all the other junk we haul around. Our Montana HC was advertised at 2175# and scales around 3500.
If I do this I'm thinking 3:73 for the mix of towing and empty mileage. Probably best to cool my heels and see where we end up with a 5th.

I'm saying the difference in mileage will be very minimal if even noticeable at all. Getting the 4.10s will just make pulling that much easier and easier on your equipment. Just my opinion.

I am trading a 2016 Ford DRW for a 2017 Ford DRW just because I want to. I am going with a 4:10 gear this time.

Chris is of course correct.

The added piece of the puzzle is that tire manufacturers are frequently very optimistic with listed diameters. Especially with truck tires.

Regardless of the diameter used, you will get a useful rpm delta between two potential axle ratios.

:-)

TxGearhead wrote:
3.73, Aisin in 5th at .77 overdrive, equals 1900 rpm at 65 mph.
3.73, Aisin in 6th at .63 overdrive, equals 1555 rpm at 65 mph.

3.42, Aisin in 5th at .77 overdrive, equals 1743 rpm at 65 mph.
3.42, Aisin in 6th at .63 overdrive, equals 1426 rpm at 65 mph.

385 HP at 2800 rpm and 900 ft lb torque at 1600.
I guess if you want to get higher HP the 3.73 looks better. The 3.42 in 6th gear is well under max torque.
My 3.42 works OK locked out of 6th, but the 3.73 looks like it would have higher HP. Something of a trade-off between more HP/torque and lower rpm for fuel mileage.

The problem with using most gear calculators is they do not use static load radius, and just ask for tire diameter. When the 15.5 static load radius for a LT275/70R18E is used, then your numbers come out much closer to what I see on my tach of around 1750 RPMs at 60 MPH. I used 31" as diameter not 33.1 with is the listed diameter.

So your number become when I applied the use of static load radius x2:
3.73, Aisin in 5th at .77 overdrive, equals 2023 rpm at 65 mph.
3.73, Aisin in 6th at .63 overdrive, equals 1656 rpm at 65 mph.

3.42, Aisin in 5th at .77 overdrive, equals 1855 rpm at 65 mph.
3.42, Aisin in 6th at .63 overdrive, equals 1518 rpm at 65 mph.


Chris

TxGearhead wrote:
3.73, Aisin in 5th at .77 overdrive, equals 1900 rpm at 65 mph.
3.73, Aisin in 6th at .63 overdrive, equals 1555 rpm at 65 mph.

3.42, Aisin in 5th at .77 overdrive, equals 1743 rpm at 65 mph.
3.42, Aisin in 6th at .63 overdrive, equals 1426 rpm at 65 mph.

385 HP at 2800 rpm and 900 ft lb torque at 1600.
I guess if you want to get higher HP the 3.73 looks better. The 3.42 in 6th gear is well under max torque.
My 3.42 works OK locked out of 6th, but the 3.73 looks like it would have higher HP. Something of a trade-off between more HP/torque and lower rpm for fuel mileage.

On edit using what I note in following post. 4th gear (1:1) and 3.42's provide 2224 RPM climbing a mountain pass a 60 MPH. 24500 LBS runs right up a 6 percent grade in 4th without a problem(except curves in the road). Why do some not want to use the gears provided in a 6 speed tranny. Run up a mountain pass at 60 MPH is 3rd gear(1.34) would have the engine turning 2980 RPMs, busy but doable. On highway 152 from Gilroy, Ca over to I-5 I was down in 3rd pulling a really windy slower section of the little pass, that was with the old 5th wheel and 22K combined.

I towed for years with a 2001.5 with a 47RE that was 325/650-700 at the rear wheels but was gear bound by only 4 forward gears, and much wider splits.

The difference with having 6 speeds forward is night and day.
I edited earlier post 60 MPH in 6th is around 1300 RPM.

I will take the low RPM's of 3.42's at 70-80 MPH any day over any lower gear ratio.

I tow at 800 pounds under the rated combined weight of 25,300 for CC 4x4 Aisin 2015 and just do not see an issue that I would address with a different gear ratio.

Disclaimer, before purchasing the truck I was sure that I would have gotten 3.73 if they were available. I now know that would have been a mistake, as they are not needed within the ratings of the truck.

And I repeat again I will take the low RPM's of 3.42's at 70-80 MPH any day over any lower gear ratio.

Chris

3.73, Aisin in 5th at .77 overdrive, equals 1900 rpm at 65 mph.
3.73, Aisin in 6th at .63 overdrive, equals 1555 rpm at 65 mph.

3.42, Aisin in 5th at .77 overdrive, equals 1743 rpm at 65 mph.
3.42, Aisin in 6th at .63 overdrive, equals 1426 rpm at 65 mph.

385 HP at 2800 rpm and 900 ft lb torque at 1600.
I guess if you want to get higher HP the 3.73 looks better. The 3.42 in 6th gear is well under max torque.
My 3.42 works OK locked out of 6th, but the 3.73 looks like it would have higher HP. Something of a trade-off between more HP/torque and lower rpm for fuel mileage.

I strongly suggest you go look at a gear chart for YOUR truck and tire size.

Figure out exactly what RPM you want to run and at what speed, and go from there.

The difference between 3.42 and 3.73 is basically nothing in RPM difference.

Again, go check a gear chart and let us know your thoughts.

mtofell1 wrote:

ependydad wrote:

Highway, I might peak into 13mpg. City driving, 10mph. Towing, 8-9mpg.

Wow, is this diesel? I do far better than that with my Hemi unloaded. Towing about the same but only 11,000#.

That is about normal for a pre DEF RAM. Chris

"60MPH is 1750 RPM with 3:42's."

Me Again, similar to my Tahoe.

Me Again wrote:

thomas201 wrote:
Have you tried taking it up to 65, let it make the shift to 6th, hold a minute and drop back to 60 to 63 where you feel comfortable? It should stay in 6th. Keep the girl that brung ya!

Then the engine would be way down on the torque curve and turned at to low of RPM for efficient towing and fuel mileage. 60 in 6th is around 1200 RPM and the engine would be lugging. I will verify that later today.

I tow at 24500 combined at 1750 RPM in 5th works very well at 60 MPH.

Chris

Thanks Chris. You got it.
Eh?