3.73 or 4.10 with 68RE for towing?

[klenger]

I've been doing some "what if" thinking (my wife hates it when I do that) regarding a new truck and was wondering what the sweet spot gearing would be with the 68RE 6 speed auto for towing heavy. I'm thinking a 3500 SRW SWB 2WD to get the max payload w/o going dually, and towing a 5er in the 12-13k catagory (Hitchhiker class). With the double overdrive with the 68RE, some interesting possibilities are available. If you look at the RPM vs Speed numbers on the worksheet on my website ( http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls ), for the 3. 73s, it looks like you could tow in 5th gear at 2100 RPM at 65 MPH all day and use 6th gear only when empty. With the 4. 10s, you're at 1800 RPM (too low?) at 65 MPH in 6th or 2300 RPM (too high?) at 65 MPH in 5th.



While the 4. 10s should be a better choice for towing, the 3. 73's are an interesting possibility if you consider 6th gear a non-towing gear only.



What say you?



#ad
#ad

 

[EMD-Run8]

I'd stick with the 3. 73s and let the transmission do the work. You ain't towing all the time and the 3. 73s will make a better everyday ratio. Looks to me like 4. 10s are a little above the torque peak.

 

[Mel Swanson]

I've been doing some "what if" thinking (my wife hates it when I do that) regarding a new truck and was wondering what the sweet spot gearing would be with the 68RE 6 speed auto for towing heavy. I'm thinking a 3500 SRW SWB 2WD to get the max payload w/o going dually, and towing a 5er in the 12-13k catagory (Hitchhiker class). With the double overdrive with the 68RE, some interesting possibilities are available. If you look at the RPM vs Speed numbers on the worksheet on my website ( http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls ), for the 3. 73s, it looks like you could tow in 5th gear at 2100 RPM at 65 MPH all day and use 6th gear only when empty. With the 4. 10s, you're at 1800 RPM (too low?) at 65 MPH in 6th or 2300 RPM (too high?) at 65 MPH in 5th.



While the 4. 10s should be a better choice for towing, the 3. 73's are an interesting possibility if you consider 6th gear a non-towing gear only.



What say you?



#ad
#ad

Thanks for that piece of work. I always enjoy your contributions to TDR members.

When I ordered my truck I assumed that 4. 10s would be the better choice for fuel economy while pulling. You verified that with the spreadsheet. However, most of my driving will be unloaded so I went with the 3. 73 ratio. I may well live to regret that decision.

mrs

 

[Wolfy]

Whoops!!

... I went with the 7. 73 ratio. I may well live to regret that decision.

mrs

:-laf



Regret is a sure, thing, I'd bet!



(but the stump-pullin will be a cinch!

 

[PGarrett]

3.73 or 4.10 with 68re for towing

Plug in the numbers with a 3. 42 rear tow in 5th should be about 1900. Before you shoot me remember peak tork is 1400 on the 6. 7

 

[Wolfy]

Goin' with the 3.73 for my particular use.

I've been doing some "what if" thinking (my wife hates it when I do that) regarding a new truck and was wondering what the sweet spot gearing would be with the 68RE 6 speed auto for towing heavy. I'm thinking a 3500 SRW SWB 2WD to get the max payload w/o going dually, and towing a 5er in the 12-13k catagory (Hitchhiker class). With the double overdrive with the 68RE, some interesting possibilities are available. If you look at the RPM vs Speed numbers on the worksheet on my website ( http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls ), for the 3. 73s, it looks like you could tow in 5th gear at 2100 RPM at 65 MPH all day and use 6th gear only when empty. With the 4. 10s, you're at 1800 RPM (too low?) at 65 MPH in 6th or 2300 RPM (too high?) at 65 MPH in 5th.



While the 4. 10s should be a better choice for towing, the 3. 73's are an interesting possibility if you consider 6th gear a non-towing gear only.



What say you?

Thanks, Klenger. Nice to have this info in easy-to-see form.



I've ordered the 3. 73, using similar thinking:

The slowest tow-speed(or unloaded speed) I expect to use on the flats, traffic permitting, will be 60 or just over (in the too-frequent 55mph zones).



This will put me just at the beginning of the top-torque range(in 6th).



Higher speeds will keep the good torque, with the higher rpm/hp for additional wind resistance, etc.



Heavier loads, headwinds or hills, of course will be covered by the lower gears.



Seems to me this offers the best potential for good mpg combined with adequate power.



Talkin 3500 6. 7/65RFE 4WD dually, two people,w/camper and (sometimes) heavy trailer boat.



I figure 4Wd double-granny, or reverse if needed (front hitch) will get the rig up any boat ramp.



With this much power and torque, I can't see the 410 as needed, at least in my case, except for exceptionally heavy (near max) hauling.



You have proposed 2-3000 lbs. more (5ver) than my rig will weigh (plus more in cab/bed?). This may change things re. the decision.



[No offense intended nit-pic on the excellent chart: Nothing indicates to the viewer that the white columns are mph numbers ;-) ]



Thanks again!

 

[Wolfy]

Peak torque auto/man

Plug in the numbers with a 3. 42 rear tow in 5th should be about 1900. Before you shoot me remember peak tork is 1400 on the 6. 7

1400 is for the manual trans.



Per chart/text on page 24 of new '07 Ram catalog (black truck on cover), Auto is 1500(looks like 1600 on diagram).



OP specified auto.

 

[Sky]

Hey everyone, Been awhile since I have posted here on TDR. I have been reading a lot on the new 6. 7 and I am just about ready to order. My 2001 has over 200k on it now so its time to get a new although I think I will keep the 2001, I love it to much to get rid of it. Anyway I was wondering if anyone could tell me what my gear ratio would be on both 4:10 and the 3:73's with 35" tires for the 68RFE? And what the RPM's would be say at 70mph?

 

[klenger]

Sky, see the link in my 1st post for an Excel worksheet that will do the math for you.

 

[Sky]

Sky, see the link in my 1st post for an Excel worksheet that will do the math for you.

Well I did but in line 10 they all said manuals so I was a bit confused?

 

[Jeb_H]

My vote on this was the 3. 73 and was what I got. This new 6. 7 is a beast of a motor and unless your going to be pulling 25-30K and often, I don't really see a need for the 4. 10 with the 68RFE and the 6. 7 motor guys...



Heck I pull my gooseneck in 6th gear quite often and with very little to no down shifting on grades too. Its really impressive how the transmission and 3. 73's work with the 6. 7...

Can't say enough about the 68 RFE as of yet.



One thing I forgot to add here about my setup, at idle speed when I go from forward to reverse or from park to reverse, the idle speed actually goes even slower when put into reverse, and with the reverse gearing the 68RFE has its awesome for backing the trailer into some really nasty places if need be LOL...

 

[Jaysyl]

Ken: Is the Hitchhiker part of the "what if" your wife likes so much?:-laf :-laf

 

[klenger]

Ken: Is the Hitchhiker part of the "what if" your wife likes so much?:-laf :-laf

Shhhh :-laf :-laf

 

[TKeeler]

4.10's Here

I plan to bump the tire size up a bit when the stockers wear out so that's why I went with the 4. 10's. I have the 4. 10's in by 98. 5 with auto and have had no regrets.

 

[MRosinski]

I plan to bump the tire size up a bit when the stockers wear out so that's why I went with the 4. 10's. I have the 4. 10's in by 98. 5 with auto and have had no regrets.

That was my dads thinking too when he ordered his w/4. 10's.

 

[cerberusiam]

Plug in the numbers with a 3. 42 rear tow in 5th should be about 1900. Before you shoot me remember peak tork is 1400 on the 6. 7

You won't tow a 12k load at 1400 rpm's on the back side of the TQ curve. The trans will find the right gear according to the programming in the ECU.



If the programming runs true to what Cummins has normally done the sweet spot should be between 2100 and 2300 rpm's. Dependinging how fast you want to go, the 4. 10's look like an excellent choice for towing.

 

[SBeretz]

Seems like both ratios would be nice for average everyday use, the 4. 10s might be nicer for really heavy trailers, whereas the 3. 73s would be nice for average 10-12K trailers traveling on the Western Highways around 70MPH. Looks like it would be a hard decision either way. 4. 10 would probably be about perfect if you were going to go up any in tire size though. Scotty