Towing sweet spot '06 w/3:73 vs '15 w/3:73

[TCollier]

I know the rear ends have been talked about plenty of times and have read most of the latest threads concerning it. But I'm trying to get an idea with a direct comparison to my current truck.

I'm probably within 2 months of getting a '15 DRW CC LB w/Aisin.

With my stock '06 2500 MC 4x4 with 48RE & 3:73 and towing my current 5th wheel (11,500#) it feels like 70 to 73 mph is the sweet spot. Where is that on the new ones with an Aisin 3:73 combo? I'm hoping to get the same feeling starting at 60 because I've heard the new trucks have a flatter torque curve. With the family in the truck, 70+ just feels fast while dragging a 38' camper. I plan on upgrading to a heavier camper in a few years too. The truck will be my daily driver though I will be doing a lot more camper towing with the new truck. I don't see me ever towing anything over 20k and the 3:73 just makes sense. But I don't won't to have to fly down the highway to feel I'm in stride.

 

[CBari]

He is my opinion and that is what it is just an opinion. My LQ horse trailer weights between 16-19k depending on how many horses we are hauling. With my 03 that has 3.73 I had to run about 72-73 to keep it from downshifting going over overpasses and small hills of course larger hills or mountain grades it will down shift. All of this is with the cruise set. Now my 13 also has 3.73 it takes running at 76-77 to keep it from down shifting on the same roads. I have a friend that has a 14 with 4.10 and his never down shift when I have driven it. His and my 13 get almost the exact same mileage pulling the same trailer of the same roads. If I had it to do over again I would get the 4:10. All that being said my truck with the 3:73 does not have any trouble pulling my trailer I just don't like it down shifting.

 

[AH64ID]

The 5.9 HPCR "sweet spot" for towing seemed to be centered around 2200 rpms, and 2000 rpms makes towing much better. Stock tires 71 is 2000, 2200 is 78.

The 6.7 is quite a bit lower due to the VGT and increased displacement... and the added 200+ ft/lbs of OEM torque. The 6.7 seems to be happy at 1800-2000 when heavy. The double OD's also really help as the single 48RE OD is pretty tall. With 3.73's 1800 is 6th is 70 and 65 is 1665 in 6th or 2035 in 5th.

If your planning to tow a heavy 5th wheel get the 4.10s.

 

[CThomsen]

I have to be going 70+ to avoid downshifts pulling either my 5er or 4 horse trailer with 3.73 gears. Not a problem on interstates. I usually just select 5tth gear on other roads with lower speeds.

 

[cerberusiam]

You will loose some MPG in DD with 4.10's but gain it towing. If you are upgrading the trailer size and doing more towing, the 4.10's would be a good choice. Will be less shifting and less strain over time on large loads. Adjust the tire size to adjust rpms but 1800-2000 is still a good choice for target rpms.

 

[TCollier]

Thanks guys. There are two trucks I'm looking at hoping they'll be around when my ducks are in a row. One has the 4:10s, the other has 3:73s. The 3:73 has the trailer prep and the auto level option which is nice. But the 4:10 is being advertised with a deeper discount and the auto level isn't a got to have item for me. This will be at least a 15 year truck. The one I have now was also going to be a 15 year truck but the wife and kids got involved in my 5th wheel camper itch and helped me scratch up more camper than truck (for long hauls anyway).
My drive to work is about 3.5 hours all interstate and highway. But I'm at work for two weeks, then home for two weeks so it's one round trip a month. The rest is short stuff around town.
So the only down side to the 4:10s I would think is the monthly drive to from work where I'm usually running about 75 to 77 mph. What are you guys with the 4:10s turning at that speed when light? Does it feel like it's too much?

 

[cerberusiam]

The difference between 4.10's and 3.73's is going to be neglible, driving style will sway that one way or another. Where you see the difference is the 3.42 to 4.10's on unloaded driving. If you are not considering the 3.42 I would not even hesitate at grabbing the 4.10 truck for better over all usage. You might gain any loss loaded as you would be able to run higher trans gear more often.

 

[RustyJC]

75 MPH with 4.10 gears (standard 3500 DRW tire sizing) will be around 1980 RPM. With 3.73 gears, 75 MPH would be around 1860 RPM. Both in 6th gear, of course.

Rusty

 

[NDanecker]

75 MPH with 4.10 gears (standard 3500 DRW tire sizing) will be around 1980 RPM. With 3.73 gears, 75 MPH would be around 1860 RPM. Both in 6th gear, of course.

Rusty

FYI: My truck runs about 1950 rpms at 70mph. At 75mph I am way over 2000 rpms. I have the AISIN and 4.10s.

 

[RustyJC]

If your truck is indeed turning 1950 RPM at 70 MPH, then it would be running 2089 RPM at 75 MPH. That's hardly "way over 2000 RPM" and only a 109 RPM difference from my calculations. Tire rolling diameters vary from brand to brand, so I'd expect some variance. The 6th gear ratios of the Aisin AS69RC and the 68RFE are both 0.63:1 (see HERE, although some other sources state 0.625:1 versus 0.630:1), so any significant variance would have to be due to tire diameter or speedometer/tachometer calibration/readout accuracy.

My calculation is from an Excel spreadsheet using (1.) the published effective rolling diameter of the tires calculated from tire revolutions/mile, (2.) rear axle ratio and (3.) transmission 6th gear ratio to determine engine RPM at a given speed.

The relative difference between the two axle ratios will remain constant. Not worth debating, AFAIC.....

Rusty

 

[AH64ID]

75 MPH with 4.10 gears (standard 3500 DRW tire sizing) will be around 1980 RPM. With 3.73 gears, 75 MPH would be around 1860 RPM. Both in 6th gear, of course.

Rusty

What size tires are you using?

OEM DRW tires are 649 rev/mile.

4.10's and an Aisin in 6th is 1956 at 70 and 2095 at 75.
3.73's and an Aisin in 6th is 1779 at 70 and 1906 at 75.

 

[Cummins12V98]

Dually towing heavy get the 4:10's lighter get the 3:42's.

 

[TCollier]

Thanks fellas.
I'll probably go for one with 4.10s. The main reason I'm looking at new trucks is because of our enthusiasm toward going farther with the 5er.
I average only 7500 miles a year with regular non towing use. I plan on towing the wheels off the camper during the summer and school holidays.

 

[mpaulson]

This is a snapshot of a spread sheet that I have. It is for the AS68RC transmission but the 6th gear ratio's are the same. So you can pick your speed and see what your rpm's would be on the left of the chart. I see that it doesn't show up in the layout that I see it while posting so it is a bit confusing and I can't find a way to share the actual excel spreadsheet here. You can see the RPM line down the middle that separates the 3.73 from the 4.10 speeds on the left.
Axle Ratio 3.73 Axle Ratio 4.10

Aisin AS68RC Aisin AS68RC
Gear 1 2 3 4 5 6 Gear 1 2 3 4 5 6

1000 7 13 19 25 33 40 1000 6 12 17 23 30 37
1100 7 14 21 28 36 44 1100 7 13 19 25 33 40
1200 8 16 23 30 40 48 1200 7 14 21 28 36 44
1300 9 17 25 33 43 52 1300 8 15 22 30 39 48
1400 9 18 26 36 46 56 1400 9 16 24 32 42 51
1500 10 19 28 38 49 60 1500 9 18 26 35 45 55
1600 11 21 30 41 53 64 1600 10 19 28 37 48 59
1700 12 22 32 43 56 68 1700 10 20 29 39 51 62
1800 12 23 34 46 59 72 1800 11 21 31 42 54 66
1900 13 25 36 48 63 76 1900 12 22 33 44 57 70
2000 14 26 38 51 66 81 2000 12 24 34 46 60 73
2100 14 27 40 53 69 85 2100 13 25 36 48 63 77
2200 15 28 42 56 72 89 2200 14 26 38 51 66 81
2300 16 30 44 58 76 93 2300 14 27 40 53 69 84
2400 16 31 45 61 79 97 2400 15 28 41 55 72 88
2500 17 32 47 63 82 101 2500 15 29 43 58 75 92
2600 18 34 49 66 86 105 2600 16 31 45 60 78 95
2700 18 35 51 68 89 109 2700 17 32 46 62 81 99
2800 19 36 53 71 92 113 2800 17 33 48 65 84 103
2900 20 38 55 74 96 117 2900 18 34 50 67 87 106
3000 20 39 57 76 99 121 3000 19 35 52 69 90 110
3100 21 40 59 79 102 125 3100 19 36 53 72 93 114
3200 22 41 61 81 105 129 3200 20 38 55 74 96 117
3300 22 43 62 84 109 133 3300 20 39 57 76 99 121

 

[AH64ID]

This is a snapshot of a spread sheet that I have. It is for the AS68RC transmission but the 6th gear ratio's are the same. So you can pick your speed and see what your rpm's would be on the left of the chart. I see that it doesn't show up in the layout that I see it while posting so it is a bit confusing and I can't find a way to share the actual excel spreadsheet here. You can see the RPM line down the middle that separates the 3.73 from the 4.10 speeds on the left.

What are you using for tire size? Your speeds seem to be about 2.5% fast.

 

[mpaulson]

What are you using for tire size? Your speeds seem to be about 2.5% fast.

Tire Specs
Size 235.00
Profile 80.00
Rim 17.00
Dia 31.80
Cir 99.90
Revs/Mi 634.22
K 0.025

 

[AH64ID]

Tire Specs
Size 235.00
Profile 80.00
Rim 17.00
Dia 31.80
Cir 99.90
Revs/Mi 634.22
K 0.025

Dodge/Ram publishes 649 rev/mile for the 235/80R17 up until 2014. In 2015 they go to 675!!! I think that is a typo, or the Nexen's are really small or soft.

634 means there is zero loss to diameter, which doesn't occur.

Those numbers also look like a direct conversion from 235/80R17 and not actual tire size. That's the general size, but each tire is different.

Look at my 245/70R19.5's

Tire size conversion puts them at 33.0"
Toyo lists inflated size as 33.2"
Rev/Mile has them rolling on a diameter of 32.3"

 

[MattandLana]

(Sorry if this comes up twice. Post vanished from my phone). Newbie question : why avoid downshifting? I wouldn't hesitate to drop a gear in a manual, for an incline, if the engine needed it. Especially given we have two overdrives.

 

[kthaxton]

I'm wondering the same thing....what's the big deal with the trans shifting down once in a while? If it's doing it constantly, I can understand that being an issue, but why is it so bothersome for it to shift down a gear on a grade?

I think with today's available torque, we are getting spoiled. I've only had mine for 6-months and I'm still giddy with the power...coming from towing with a half ton gasser.

 

[MattandLana]

I'm still giddy with the power...coming from towing with a half ton gasser.

I'm with you there! I was in a Toyota Landcruiser 100 series tdi. Superb machine in its class, but boy oh boy I'm grinning lots with this freight-train of power. Hope I get used to it eventually because my mileage is suffering big time. I keep planting the foot away from lights - yeehah!