3.73 or 4.10 gears?

[eridenour]

Buying new '06 CTD 4x4, auto, and planning on 4. 10 gears for 35" tires. According to a chart it looks like the 4. 10's turn 2200 rpm @ 81 mph, and the 3. 73's turn 81 mph @ 2000 rpm. What engine speed do you folks like to run your diesels at on the highway? This will be my first, long sought after diesel.

 

[Dieselnerd]

I've got 4:10's for towing, I don't drive 80 MPH. Cruising at 2000 or 2200 will make little difference to your engine. You MAY get slightly lower mileage with the 4:10's or you MAY NOT. Depends more on your driving style than gear ratio and how heavy a load you have. I've always had 4:10's on my Cummins, better performance taking off and better hill climbing with a trailer. If you don't plan to tow anything heavy the 3:73's will probably work fine.

 

[nick05]

i had a ram gasser 5spd. with stock 3:55 gears and 35's and i couldn't go anywhere in 5th on the xpress way. just bog. even in 3rd which is 1:1 until i get up over 2500rpms. so i would go with the 4:10 because your speed will be closer to the speedometer than 3:73's and you will have much better response with the taller gears. ideally with 35's you want 4:56 gears that come in the new power wagon but minus the great engine. i agree as above that the higher rpm's the lower the mileage.

 

[cerberusiam]

If you are set on 35" tires get the 4. 10's. The auto, 3. 73 and 35" tires is not a good match. Low speed driving mpg will suck, its really hard on the trans and TC, OD is useless for anything over 3k, and anything under 70 mph causes way too many up and down shifts.



If you can live with a shorter tire do not intend to tow much over 15k GCVW then go with the 3. 73 gears. Driveability and mpg will be much better.

Cruising at 2000 or 2200 will make little difference to your engine

Only if you consider 2-3 mpg little difference. The sweet spot for 610 HPCR is about 2000 rpm's. Below 2000 your getting into lugging and harmonics. Above 2000 the mileage starts to go down. Try to tailor your rpm's to around 2000 for sustained empty driving and 2400 for sustained towing rpm's and you will be close to having the best of both worlds.

 

[10-9jc]

Decisions, decisions -

I have an '05 3500, SRW, 4 x 2 - with 4:10 - cause I plan to

tow a heavy 5th wheel. With the stock tires, 70 mph is

right about 2100 RPM.



If you are going to haul, tow heavy loads, go with the 4:10.

If you're going to do a lot of driving empty - no load, or light loads -

the 3:73 would be fine.

With either, taller tires will raise the overall ratio, and lower the RPMs.

And . . . unlike the '05, whichever you decide on, you will be able to

lock out OD if you wish. [If I had that ability, think I would have 3:73].

JC

 

[Hoefler]

I have stock tires and 3. 73, I tach at 2050 at 70 mph in overdrive

 

[Nate]

To give you an idea, 35s and 3. 55s... 70mph is 1600rpm. It sucks pulling a trailer.

 

[klenger]

You want the 4. 10's.

 

[Bertram65]

If you are getting the auto 4. 10s are the only gears to have. From experience with my truck the 2000rpm as the turing point for mileage is a myth, I have run whole tanks of fuel empty at 1900rpm up to 2500rpm and all between and noticed very little difference in mileage. As far as towing anything less than 2000rpm and you will be downshifting to 3rd on the hills. With the auto, 4. 10s and stock tires I am running 2150rpms at 70mph that is about as fast as I feel safe towing, and I can hold that speed on most hills. With the automatic 4. 10s and stock tires are the way to go if do any towing, you can up the power if you put on 35" tires but you will be shortening the life of the automatic.

 

[jwduke]

I tow a 8,600 lb 5er with 3. 73's with no problems, but I think if I was going to fulltime, I would have 4. 11's.

 

[JEly]

http://www.dakota-truck.net/TIRECALC/tirecalc.html This is a program that helps you decide what size tires and gear ratios



JIM

 

[mconstable]

I can tell you for a fact that my mileage drops pretty quickly at and above 2000 RPM,s.

i have an '03 6 spd. with 3. 73's that I love, but when towing I'd like to have the 4. 10's, and if you're going with any tire bigger than stock, I'd recommend the 4. 10's hands down.

 

[sweeda]

i've had two (2) trucks with an automatic trans. and changed both to the 4. 10 rear gear. because i haul a load of about 1000 to 1500 lbs. all the time and the stop and go traffic killed the average mpg. after the change i increased the average mpg to 14. 8 from the 13. 5. you must be honest with your type driving. on long trips 80 miles or more 3 times a week the 3. 73 is what you want. shorter than that with a lot of city driving with an auto trans do your self a favor and go with the 4. 10's. manual trans are a lot more forgiving due to you the driver can do the gear selecting and not the computer.