4:10 or 3:73 ?

[TxGearhead]

Possible upgrading to Ram dually. I'm pulling 12,500# gvw with SRW and 3.42 rear end. Usually lock 6th gear out. Plan is to move up to new 15,000# gvw 5th. Not sure if I want to get 4.10 or 3:73.
Whata ya think?

[bluegrass_smoke]

The tire size is 245/75SR17.

So far what I am reading is the truck will work with either gear ratio since the weight is 16500? The 3.55 will make less RPMs when driving at highway speeds without the trailer load?

I am a wood/building guy, I know where the fuel goes in on my truck and that's about it.

[4x4ord]

bluegrass smokers wrote:
OK someone help me out here and let me know if this is the correct line of thinking. With a 4.10 I can tow easier but driving unloaded the truck will work harder at high speeds and with the 3.55 it works harder towing but easier at unloaded highway speeds? Basically right? My fifth wheel is about 16500lbs.

I am looking at 2 2017 Ford DRW F350s. Both trucks are close on equipment but the rear ends are different. I am trying to figure this out. And the truck will have to be my daily driver along with family trips without the fifth wheel.

The 2017 DRW with 3.55 gears is rated to handle a 27,000 lb trailer. You don't need to consider 4.10 gears for a 16,500 lb trailer. Even the 2017 SRW is rated for an 18,000 lb rv with 3.55 gears.

The weight of the trailer, the wind resistance and incline of the road determine how much power is required to tow your trailer. The gear ratios just allow the engine to run at a suitable rpm. If your towing a 16,500 rv down a level highway you only need to be making about 100 hp. The 6.7 can produce 925 lbft of torque at 1600 rpm. That means it is capable of making 282 HP at 1600 rpm. This engine can very easily handle a 16500 lb trailer. Your tire size and speed dictate the rpm of your rear axle...so a 2017 Ford dually at 60 mph will have its rear axle turning 640 rpm. With a 3.55 axle ratio the transmission can select any of any of 4 different gears to obtain that rear axle speed:

3rd gear - the engine will be turning 3453 rpm .... it might select 3rd gear for grade braking going down a steep hill.

4th gear - the engine will be turning 2613 rpm ... it will select this gear for pulling up a steep hill where maximum power can be obtained. This is a good gear to be in when the engine is working hard as there is the least amount of power lost in the drive line while running in 4th gear. (the ratio which is closest to 1:1)

5th gear - the engine will be turning at 1954 rpm....the transmission will select this gear in a high wind situation or when pulling up a moderate hill.

6th gear - the engine will be turning 1522 rpm ... this gear will be selected while cruising down the highway, pulling in light winds or slight inclines.

[goducks10]

Which size tires are on the truck you're looking at? That will make a difference in what RPM's you'll see.

[john_bet]

Wow, 7 pages of discussion about ratios. Guess I will just keep my '04.5 5.9L 325 HP 600# torque,3.73 ratio truck with 210K and counting. I tow 19-20K combined at 65 MPH and 1800 RPM on the interstates or two lane roads where allowed at 10-11 MPG. I mostly tow from Indiana to east of the Rockies, west central Montana. Current trip has taken us from Montana thru the Black Hills into Colorado and on into eastern N.M. I have towed from Utah on I-70 to Indianapolis with this set up and not worried. Current trip will take us across TX, Ok, to Tn., to southern ILL, to Indiana on US-50 to home. Oh, the best part about the truck is it has been payed for for years. Good day ye all.

[RCMAN46]

bluegrass smokers wrote:
OK someone help me out here and let me know if this is the correct line of thinking. With a 4.10 I can tow easier but driving unloaded the truck will work harder at high speeds and with the 3.55 it works harder towing but easier at unloaded highway speeds? Basically right? My fifth wheel is about 16500lbs.

I am looking at 2 2017 Ford DRW F350s. Both trucks are close on equipment but the rear ends are different. I am trying to figure this out. And the truck will have to be my daily driver along with family trips without the fifth wheel.

If we use the Cummins with the Aisin transmission when going about 60 mph.

Rpm with 3.42 in 5th gear 1712
Rpm with 4.1 in 6th gear 1680

If anything the Ram will do better with the 3.42

16500lbs will be nothing with all three of the current diesel pick-ups with any of the available rear gears.

[bluegrass_smoke]

OK someone help me out here and let me know if this is the correct line of thinking. With a 4.10 I can tow easier but driving unloaded the truck will work harder at high speeds and with the 3.55 it works harder towing but easier at unloaded highway speeds? Basically right? My fifth wheel is about 16500lbs.

I am looking at 2 2017 Ford DRW F350s. Both trucks are close on equipment but the rear ends are different. I am trying to figure this out. And the truck will have to be my daily driver along with family trips without the fifth wheel.

[Me_Again]

I owned a 2001.5 with 4:10 gears for 14 years. I have to say after getting the new RAM, I would never want to have to be limited on ease of freeway cruising again.

[jaycocamprs]

RCMAN46 wrote:

Never understood why we have to tow in 6th gear or the top gear.

That is the whole purpose of a transmission. I agree the 3.42 is the ideal rear gear for the Cummins with the Aisin.

Unloaded as said you can cruise at a comfortable and fuel saving rpm even at 80-90 mph which I often see out here in the west with speed limits at 80 mph.

Never said I have to tow in high gear. What I was trying to say is not everyone needs the gearing for high speed unloaded use. Gear for the speed you drive. The amount of non towing miles that I drive my truck is very low, and most of that is below 60. And I get that seat of the pants the 3:42 in 5th is equal to the 4:10 in 6th. Either would be a big jump from the 305 hp 5 speed truck I now have. I would rather have the extra gearing down low, even though I know it's not really needed.

[RCMAN46]

Me Again wrote:

jaycocamprs wrote:
The DW and I have begun talking about replacing the current 05 Duramax with a new truck. Question is another GM or the Ram, it won’t be a Ford. I get what yall are saying, at the 12k scaled weight that we are running I could get by with a SRW 6.4 Hemi. But we have a DRW diesel truck, and we don’t want less than we now have. I know that the Cummins with a 3:42 will pull this or even a larger trailer just fine. I also don’t need a DRW truck that cruises 80 MPH empty. I just don’t drive that fast. In this part of the country that will get you face time with a LEO, and that is something I try to avoid. Fact is I want a TV pull my trailer up to 65 MPH in comfort on cruise control. I rarely drive my current truck long distance or on the interstate not towing. I have other vehicles for that. So a truck that won’t shift into top gear below that speed towing does not make sense to me. So if a Ram with a Cummins and 4:10 gear tows it like it’s not there, it’s ok. I won’t come back and complain about having too much truck. And if we ever buy a larger trailer, I won't have to worry if I have enough truck.

You are still not understanding the beauty of the 3:42's and Aisin tranny. You do not have to be in 6th to tow 65 RPM with the RAM set up that way. 5th will be about the same RPMs and 4:10's in 6th.

Unhook the trailer and you cruise at comfortable low RPMs in 6th at 60, 65, 70 etc. It will shift to 6th at lower RPMs when not in tow haul.

Chris

Never understood why we have to tow in 6th gear or the top gear.

That is the whole purpose of a transmission. I agree the 3.42 is the ideal rear gear for the Cummins with the Aisin.

Unloaded as said you can cruise at a comfortable and fuel saving rpm even at 80-90 mph which I often see out here in the west with speed limits at 80 mph.

[Me_Again]

jaycocamprs wrote:
The DW and I have begun talking about replacing the current 05 Duramax with a new truck. Question is another GM or the Ram, it won’t be a Ford. I get what yall are saying, at the 12k scaled weight that we are running I could get by with a SRW 6.4 Hemi. But we have a DRW diesel truck, and we don’t want less than we now have. I know that the Cummins with a 3:42 will pull this or even a larger trailer just fine. I also don’t need a DRW truck that cruises 80 MPH empty. I just don’t drive that fast. In this part of the country that will get you face time with a LEO, and that is something I try to avoid. Fact is I want a TV pull my trailer up to 65 MPH in comfort on cruise control. I rarely drive my current truck long distance or on the interstate not towing. I have other vehicles for that. So a truck that won’t shift into top gear below that speed towing does not make sense to me. So if a Ram with a Cummins and 4:10 gear tows it like it’s not there, it’s ok. I won’t come back and complain about having too much truck. And if we ever buy a larger trailer, I won't have to worry if I have enough truck.

You are still not understanding the beauty of the 3:42's and Aisin tranny. You do not have to be in 6th to tow 65 RPM with the RAM set up that way. 5th will be about the same RPMs and 4:10's in 6th.

Unhook the trailer and you cruise at comfortable low RPMs in 6th at 60, 65, 70 etc. It will shift to 6th at lower RPMs when not in tow haul.

Chris

[jaycocamprs]

The DW and I have begun talking about replacing the current 05 Duramax with a new truck. Question is another GM or the Ram, it won’t be a Ford. I get what yall are saying, at the 12k scaled weight that we are running I could get by with a SRW 6.4 Hemi. But we have a DRW diesel truck, and we don’t want less than we now have. I know that the Cummins with a 3:42 will pull this or even a larger trailer just fine. I also don’t need a DRW truck that cruises 80 MPH empty. I just don’t drive that fast. In this part of the country that will get you face time with a LEO, and that is something I try to avoid. Fact is I want a TV pull my trailer up to 65 MPH in comfort on cruise control. I rarely drive my current truck long distance or on the interstate not towing. I have other vehicles for that. So a truck that won’t shift into top gear below that speed towing does not make sense to me. So if a Ram with a Cummins and 4:10 gear tows it like it’s not there, it’s ok. I won’t come back and complain about having too much truck. And if we ever buy a larger trailer, I won't have to worry if I have enough truck.

[dubdub07]

The charts and data are not in perspective as values are different. The Cummins has a redline of 3K. That is a short and flat power curve, really. The 8.1 doesn't compare to the diesels.

The Duramax is a sweet motor and I love the GM trucks. But I will stick to my Cummins. I do not care if my 8.3 or 6.7 Cummins is popular with the "in" crowd, I just like that they keep plugging along, cool and quiet.

W

[Me_Again]

RCMAN46 wrote:


If anything the 8.1has a flatter torque curve than the Cummins.

At less a half of the Cummins.

Chris

[RCMAN46]

The Cummins torque curve looks more like the 8.1 than the Duramax.

If anything the 8.1has a flatter torque curve than the Cummins.

It is interesting that the Duramax gets to max torque at a lower rpm than the Cummins.

[dubdub07]

I would stay with the 3.42s. The new transmissions compensate for the lower rear end. IF I DID......go ahead and take the time to swap them out.....I would go straight to 4.10s.

William