I am not 100% sure but o/d on the 03's locks the trans in 3rd. I have an 04 Tow/Haul button. I only loose over drive. At 60 (4.56 gears) 2300. I also pull about 8000 lb travel trailer. I did the re-gear specificly for towing. I am sure someone with more knowledge will jump in.

 

On my 03' I dont have a tow/haul button. Just a o/d off button. If I push that button my torque converter will lock in 3rd gear and I will loose 4th and 5th gears. At 60 mph the rpms are right at 2500 with the torque converter locked and the o/d button pushed. You say you are running 2300 rpms with 4.56 gears. Is that with your tow/haul button pushed or not?? When you say you only loose overdrive are you saying you loose 4th and 5th gear? Or do you just loose 5th???

 

The FIRST best thing you can do for towing is to lose those 20" wheels. First of all, by DODGE specs, towing capacity is 1000 lbs. greater with 17" wheels vs. 20" wheels. There are a few reasons for this: A) stock tire size on 20s is larger and the larger a wheel, the lower you effective gearing becomes. B) Even with the same diameter tire, sidewall and air is lighter than steel and without doing a physics lesson - 10 lbs. of extra weight on a wheel acts like 50 lbs. on the engine so take this times four wheels. C) The farther out from the hub the weight is placed, the harder it is to rotate that mass (also physics).

Yes going to 4.56 gears will help immensely, but going from 20" wheels to 17" wheels will help considerably as well.

BTW: I tach 2050 at 70 MPH with 4.56 gears, but I run 35" tires. As I stated, larger tire diameter lowers effective gearing, so even though I have 4.56 gears, after compensating for tire size I'm running like I have 4.11 gearing. IF I stayed with my stock 3.92 gears after going to 35" tires, my effective ratio today would be a pathetic 3.52:1 which I had - for all of about 10 days and I felt like I couldn't get out of my own way, LOL...

 

Hey Hammer, thanks so much for your reply. I have been researching this dilemma for months, and I originally came up with the idea to switch to 17 inch tires like you mentioned......then I found this on the net. (Dont get me wrong, Im not arguing, and appreciate everyones input). Does this open up more discussion.....???

This is a copy and paste from ;

http://www.outbackers.com/forums/ind...pic=29961&st=0



A 275/60/20 tire makes 634 revolutions per mile. If you times this by the gear ratio, 3.92 the driveshaft would spin 2485 times in a mile.

A 265/70/17 tires makes 658 revolutions per mile. If you times this by the gear ratio, 3.55 the driveshaft spins 2335.9 times a mile.

The 20 inch wheels give you a better towing ability since the driveshaft spins faster. This means that a 20 inch spec'd dodge has a lower final gear than the 17 spec'd dodge.

Now if we go to a 17 on a 3.92 ratio. your driveshaft would spin 2579 times in a mile. This would also increase towing capability.

But as you can see its less than 100 revs more per mile going to the 17/3.92 combo.

WHY? The 17 inch wheel uses a 31.7 tire versus the 20 that has a 33 tall tire. There is less difference using a 33 versus a 31.7 tall tire than using the 3.92 versus 3.55 ratio.

It is not going to be worth your time and money to switch your 20 inch wheels back to 17's. Just not enough difference

 

JJ Tow/Haul Engaged (Dash light on) . You don't want to tow. with o/d or tow/haul which ever you have engaged. Way to hard on the drive train. And I only loose 5th. Shoot me a PM if you need more info. I'll give you as much as I can.

 

Towing in OD won't kill you unless you're in a hilly area. It hunts for gears too much and heats up the gear box. That's the only reason they say not to tow in OD.

 

This guy is using proper math but not taking all factors into account. First of all, he's not even factoring the sheer weight of 20" wheels vs. 17" wheels PLUS his using completely different variables because of different tire diameter. To give true numbers you need to assume the same tire diameter - a 33" tire is 33" in diameter whether it's on a 15", 17", 20" or 24" wheel.
His other MAJOR flaw is that nowhere is he accounting for higher engine RPM at a rated speed when going to taller gearing. So his "less than 100 revs per mile" theory is all wet because assuming traveling at the same speed, the engine RPMs will be higher when gearing is numerically higher so that "100 revs per mile" will be dramatically higher - increasing power/towing capacity much greater than he claims. Again, he's using proper math, but NOT factoring in nearly all the variables that come into play.

Go to Dodge - where THEY spec a 1000 lb. greater towing capacity using a 17" wheel vs. a 20" wheel. I think the guys who make the thing would know.

 

Ok, thanks for all your help Hammer. Problem is I have two sets of 20's, nice set for summer, older set for winter. Will think about it.

Back to my original post...When towing my trailer, with OD off, (about 60mph) Im usually running torque converter unlocked(unless down grade or tail wind).

With my current 20's and switching to 4.56, would you guess the trans controller will allow the converter to lock in 3rd???

If not, Im probably going to be running 3400 RPM at 60 mph.

 

Why you'd get a 2nd set of 20" wheels for a truck designated for tow use is beyond me, but it is what it is. There is a reason 3/4 and 1 ton trucks ship with the smallest wheels that clear the calipers. IMO running 20s makes 4.56 gearing all the more important.

No, with 4.56s and 33" tires you'll be taching somewhere around 2100 rpm at 65 if my math is right. I'm taching 2050 at 70 with 35" tires and 4.56 gears.

 

Got the second set of wheels....prior to becoming a tow vehicle....

Hmm, with OD off and torque converter locked, Im running 2500 RPM now as it is....with 3.92 ???