advice on gear ratios

[Fireman]

I have a stock '01 auto-3. 55 and I tow !0-12K depending on how many toys I must have. I know I'm over the GCVWR. I am very unhappy with this setup and plan on ordering a new truck with a 6 speed man. I calculated vehicle speed/engine speed based on 265/17s 3. 73=70mph @2002 rpm and 4. 10= 70 mph @ 2200 rpm. I'm concerned with fuel economy ( 300 rpm can make a 1. 8 mpg difference on my current rig loaded) but I want enough gear to pull the load. Who has towed with a 3. 73, what is your opinion? Who has towed with an auto and manual, is there a big difference? Any other opinions or advice? I don't want much, just to be able to easily pull my load and get the best milage possible.

Thanks
Fireman

 

[TowPro]

you only have 2 choices, and I have the 3:55's with a 5 speed. I tow an 11K 5er and love it. 1st is only good to get rolling as its so low, The 6 speed would be nice as it fills a gap I have between 3rd and 4th if I heard right.



I get around 20 MPG empty with the 3:55's

 

[Rob Thomas]

fireman,



I tow pretty much daily with a variity of weight. I have the 3. 55's and the 6-speed, and love it! I have no complaints about the set-up I have, I cruise at 80mph @2000rpm, keep in mind I have 315 75 R16 tires and still have no complaints, however smaller tires would be even better, but I dig the 315's. I would never get the 4. 10's, don't need 'em. Hope this helps



Later, Rob

 

[cmckinney]

3.55 5-Sp 265/70/16

I have the 5-Sp 3. 55 with the stock wheel and tires and at 70 MPH I'm right at 2000 RPM how do you get a tad over 2000RPM with 3. 73 gears? Seems like it would be closer to 2125RPM

 

[Fireman]

Thanks for the replies. I'm looking at the 03's and 3. 55s aren't an option. The figures I quoted were only calculations, but keep in mind that the new trucks will have 17" wheels and tires. The only way that I can keep my rpms above 2000 is to run 80 mph and that is too fast for me on SRWs with that load. Anybody out there run 3. 73 ?

Fireman

 

[Fireman]

cmckinney,

The OD on the auto is slightly taller than the manual therefore I turn slightly less than 2000 @ 75 mph. This makes great mileage empty but it doesn't tow well in OD and I hate using 3rd

Fireman

 

[BarryG]

My personal opinion is go with the 373'S. DC should have been offering those from the git go. The 354's are a little to low and and the 410's are little to high. I have had 373's in several trucks in the past and thought they were great. Even my last dodge had the 390's in it and I liked them better than the 410's I have had in the past.

 

[pwknapp]

Don't get the 4. 10's. After paying at the pump for over 410K I sure wish I had gotten 3. 55 or the new 3. 73's. At 70 with 235/85 tires I am at 2450 rpm. The torque on the CTD more than compesates for a bit lower rpms, and the fuel savings can surely be used elsewhere.

 

[Fireman]

Thanks

I asked alot of guys that pulled rvs about their ratios and trans, and the overwhelming majority said that 3. 55/auto pulled great ( they also claimed 16 mpg towing). I was worried that the4. 10s would be too low, so I got the 3. 55s and the auto and have been unhappy every time I tow. That is a pretty costly mistake that I dont want to repeat so I appreciate all of the input. Now its time to take the big plunge again.

Thanks all
Fireman




i

 

[BILLYGEE]

Perfect set-up as i see it

The six speed is the ultimate for towing, but as I understand and like it... the new Common Rail Cummins HO with the new 5555555peed Automatic is the way to go... 3. 73 sounds closest to about right. Guys with the older trucks I would order or prefer the 4. 10's and go with larger tires to get the final ratio just right and change the alb computer to compensate(I don't know if the 3500's can do this-my '98 I couldn't).

My '98 3500 w/5 speed and 4. 10's and 235 tires was just about right except for the missing gear(I figured final drive ratio about 3. 90). That truck(24V) turned it's best 19mpg empty and towed everything I had and got 10-15 mpg towing at 70-75mph... My 2001 w/auto and 3. 55's best empty 20mpg, towing my 6000# 22' travel trailer at 60-80 and mostly out of od because of heavy and slower traffic just did 12mpg. Both are 4WD.

The 4. 10 3500 was turning 2500rpm at 75mph which is the range that the current CTD purrs the best but generates a lot of engine noise in the cab which ain't no good if your'e trying to listen to your favorite Alan Jackson CD and sing along to it and the little lady thinks I'm deaf! Oh well, go figure. The 3. 55 w/auto does less than 2000 rpm at 75 and ain't at it's best towing a load there but the engine noise ain't there. I THINK WE ALL WILL SEE DC IS LISTENING WHEN THE NEW QUIET QUIETER, STRONGER CTD w/5spd(PROBABLY MERCEDES) AUTO W/4DRS is a nice pkg. MY . 02 BILL GOo.

 

[DHawthorne]

Just finished a 1700 mile trip with my 5fer. The truck is stock with 3:54's. My 70 mph rpm is 2000. 235x85x16 Michelins. Fuel mileage

light varies depending on speed. Generally around 17. 5-18. Good fuel in other parts of the country will yeild 19-20. No good fuel in FL.



Towing at 55 is tow much load on engine in OD with the 6sp in my opinion. When I have run 55 I do it in 5th gear and show 13-14 on the computer. In OD 11-12. 62-65 seems to be the best for mileage in OD. Above that its 10mpg. If you have ever been to New Orleans and crossed the Industrial Canal Bridge on I-10, you know its a good grade. How much grade I don't known. Going over I tried in in 6th and hit the bottom at 65mph, just under 1900rpm. Before I half way up I had to downshift to 5th. Coming back I started at the bottom in 5th at 63-65 (2250-2300 rpm) in fifth and never lost a mph.



That told be alot. For me one of two things must happen. Either I install the EZ and hope the extra HP and torque will carry the load, or go lower to 4:10's. I will loose on the road running light, somewhat. In towing gear, I think I would be able to run 65mph at 12 or better with the 4:10's. I'm leaning toward the Easy right now because of mileage. I also like running down those power chokes with 3:73's, even when I give them a head start with the higher rear which makes the torque and hp come on hard in the top end.



Dave

 

[Fireman]

And the winner is.....

3. 73. I went to the dealer to order and told them that Iwanted to drive a 6 spd before I orded. They had one '02 with a 6 spd left, so I got to drive it, Wow! I couldn't belive the difference. That was a 3. 55, so I believe (hope) the 3. 73 should fill the bill, I'll let you know in a couple of months.

Thanks again
Fireman

PS
it's gonna be RED

 

[Jumbo Jet]

I will only have a TRUCK with 4. 10 gears, 4x4, and Limited Slip. Just a personal preference from years of owning pickups and pulling loads. Had a 1973 Dodge Adventurer SE 360ci with 2. 94 gears. Would move down the road, but never pulled much with it.



You can hardly justify the expenditure for the GearVendors Overdrive, but it sure is a great addition to my Auto with the 4. 10 gears.



With transmission OD off and GV OD on, my RPMs are 2,250 at 65mph pulling my 9,000lb. 5th wheel TT. I've found that to be a great RPM while pulling. Very little RPM and MPH loss even on tall hills.



3. 73 will be a real good ratio for a lot of people too!

 

[klenger]

I really like teh 4. 10's for pulling our 5er, and I am now getting about 19 MPG driving empty around town on the freeways. I don't think that the MPG loss with the 4. 10's is as big of a deal as a lot of people think, and it sure tows great. I think the engine is getting quiter at higher RPM's now that I have a few miles on the truck.



I'm not sure if 3. 73 would be the trick or not. Might be too low for towing in OD, and still too high for running empty. It'll be interesting to hear reports for that combo.

 

[DHawthorne]

I fully agree with you guys that tow with 4:10's. Two of my last three trucks had 4:10's. 4:10's is the right gear for getting the load down the road with the ISB. My last truck was a 96 CTD with a 3:54 rear. I really got use to the 22-23mpg on the hyw. I gave that to my son and bought the the 2000 ISB with the six speed. I known the big rigs have gone from lower gears to 3:54's. Our Kenworth twin screw

has 4:10's with a 13sp. The truck has a Cat 3406 @ 400HP. It has enough HP to pull the 3:54's with the load we carry.

Just have not changed them out yet. I just feel the extra HP with the EZ may be enough to do the job without changing the rear. If the EZ don't do I will drop the rear end to the lower 4:10 Ratio.



Just a note and not criticism but rear ratios are backwards when speaking HI and Low. A low ration rear would be one like a 4:10 or 4:56. A higher ratio

rear would be 3:73 and 3:54 would be a higher ratio. Lower ratios turn the drive shaft more at the rear. 4:10 turns the rear axle one time for every

4. 1 times on the drive shaft. 3:54 is 3. 54 times on the shaft to the rear axle rotation. Because the 4:10 requires more imput from the transmission than the 3:54, it is said to be a lower ratio causing the engine to turn more RPM's at all speeds. The 3:54's which is a higer ratio requires less imput and lower rpms at all speeds resulting in better fuel mileage.



Again this is not criticism, just information.



Dave

 

[Steve M]

I had a '95 auto with 3. 54 ratio. It was pretty sluggish with only 160hp/400lbs/ft torque. But it was quiet and nice for the long trips. I traded it for a '98 5spd/4. 10 12v. It was like night and day for towing on the interstate at 70. Nothing slowed us down. But at 2500rpm for 10 hours a day, the headaches ruined the trips for me. Mine was acceptionally noisy for some reason. I drove others with 5spds that weren't nearly as loud. So at 89,000 trouble free miles, I traded for another auto/3. 54. With 235hp and 460lb/ft of torque, we do ok towing our 5th wheel. I can lock out O/D at 65mph and be in the same rpm as the 5spd/4. 10 at 70mph. To me it's like the best of both worlds. On all but over 4% grades, we cruise at 68mph/1800rpm. It's quiet and 13. 5mpg ain't too shabby. Over 4% grades I lock out O/D and climb at 2500 rpm. So really nothing slows us down now either. Just my humble opinion based on our own experience with both ratios.