I am a fairly new member here and so far have been mainly just looking and learning. I bought the truck in my sig a couple of months ago and will retire my Ford as soon as I get this one rigged out to pull my 5er. I bought a used superglide hitch that came in late yesterday and will be installing it this next week.

My problem is that when I bought this truck it had a lift and 35's on it. I have noticed that the RPM's are about 1600 @63-65 mph, will the 35's force me to change the gears or will i have enough torque to tow my 5er. Will it drop out of OD on every small hill? How will it affect MPG's? I really like the way the truck looks just like it sits and don't want to have to take off the lift or the tires. Give me your thoughts guys.

 

I looked up the specs for your trailer and 10500lb empty with 13993lb gross. My last trailer was a Cardinal just under 12500lb gross and my truck had a hard time pulling it. No mods and stock 245 tires but 3.55 gears, I would have to change down (5spd) on most small hills and EGTs up to the amber. With a tail wind it would tow very well but hills and or a head wind

 

I regularly pull 18K, no problem as far as power. I have a 6 speed, on hills I am usually in 5th (which is the towing gear), have yet to have to shift down into 4th. My EGT's are right around 1K on steep hills.

I cannot tell you about how an automatic does, but probably OD is not your towing gear.

I generally get right around an average of 15mpg's pulling that 18K load.

CD

 

Sounds like you have the 48RE with 3.73s. With the 35s at highway speeds pulling approx 14K you will probably find you will be unable to hold OD on the hills. The six speed (G-56) manual guys will have a little easier time with the bigger tires because of the gear ratios of the G-56 (acts more like 4.10 gears).

 

I pull my 34 ft Challenger - 11000 dry weight - as much as the average person. I took it last year to Alberta and south thru Great Falls Montana, Butte and Boseman. There are some pretty nasty, long inclines and declines there. Cant remember the grades on them, but posted speed on the down was "25mph if over 10000 pounds". It actually handled it better that i thought it was going to..... it shifted out of OD, then I would turn OD off so it didnt jump back and forth. Your not going to win any races in the hills. But it will do it. Just take your time and dont push it hard. 3.73 and 35's are nice to cruise with on the hiway, as long as there isnt a huge wind.

 

This is what I'm figuring also,(that the truck has 3.73's). I have a very heavily modded 7.3l that i have been pulling with (it has 3.73's and 33" tires). The rest of the guys that I travel with all have the Dodges and they seem to tow very well and I had been pulling the race car trailer with the brother in laws mega and loved the way it pulled bone stock so I bought me one. If I were to change the gears in mine to 4.10's, would it help or hurt the MPG's while towing? while empty? Would I then be able to keep the auto in OD when I get into the hills and the truck be able pull like it did when it was stock? Thanks in advance for the responses.

 

Very good info. Where I live it is as flat as a table top so I don't really have a place to test out my set up before leaving out on a trip. I have no illusion of pulling a mountain in OD just didn't know if it would kick out at the first little incline.

 

With the 4.10s, I think you would have a better time pulling with 35s. But that route may be very costly. It really does depend on what you primarily use your truck for. If you tow often, the 4.10s may be the way to go. If you drive unloaded often, the sticking with the 3.73s would be the best choice. Also, the speed at which you travel on the highways is going to have a significant effect on your mileage. If you enjoy 75 MPH, the 3.73s are a better choice. If you stay in the 60-65 MPH, the 4.10s. Like others have said, you can pull with the 35s, just requires action on your part by switching off the OD on the hills, and probably some energy management on the smaller hills. Since your truck already has the 35s best bet would be to head out and give it a try. Worst case, you could sell off the 35s and downsize to a 33. Like you already know, just don't want the truck to continually kick out of OD and heat up the trans.

 

I think you're right. I guess I'll probably know a whole lot more about it when I get the hitch installed and can get out and give it try and it won't cost anything to give it a try. I am not so much worried about the labor cost to install the gear sets as I am the cost of hard parts. I think I'd have to strongly consider putting in new ball joints, updated steering etc. while I'm in there. Again, Thank You for your response.

 

I asked Cummins about the recomended RPM range for the ISB, and they basically said it shouldn't be run with a load below 1600...

If you are turning 1600 at highway speed, I'd bet you will be downshifting quite a bit.

There's nothing to loose trying it as it is, but if it is going to tow with the 48RE and 3.73's and those tires, I suspect you might be happier if you converted to 4.10.

 

I was in your situation not that long ago. 35's and less weight, 7k, yet more hills for sure. I hated it. Tried the OD off, and it did fine. But it reved to high for decent mileage. I ditched the tires for OEM sized. It is the bomb now. With no load it would downshift on some hills (35's) adn now it pulls great.

Like others have said, try it, costs nothing. But have a contingancy plan. The difference between 35's and stock tires felt like I picked up 50-60 hp.
I had 65hp box at the time, wasn't enough. Felt like I had to tow at 70-75 with the 35's just to be in the power.

Good luck

Changing tires was cheaper for me, I actually made money in the trade from 35's to OEM. And lots less $ when it comes time for replacing them.

 

Thanks for all the replies guys. I'll be installing the hitch tomorrow and may drive it to Houston to pick up a brake controller the next. I'm suspecting that it will be as most have suggested that the rpm's will be too low. In the case that it is too low, I'll have to make a decision on whether to ditch the lift and tires for stock stuff or go to 4.10's.

 

WhiteMule,

The 35s are a bit tall for heavy towing, but you can just run in Tow/Haul when needed.

Two problems with tall gearing and the 48RE. One is the 1st gear is a bit high. So starting out with a load on an upgrade is slower than I'd like it to be. And the OD gear is so high that you have no throttle response left. The TC lockup clutch is the weak link in the system so be careful! Try to keep your pulling RPM up around 2000 or 2200 when you are on a grade. My TC clutch began to slip at 1600 RPM while towing my 9000 lb trailer. Don't let this happen or it will be toast. It seems like you can pull in any gear if you have to with the Cummins, but if you give the tranny a break it will be happier, and higher RPM helps it.

I have the 3.73 gears and am running 1500 RPM at 60 MPH. It's tall for towing heavy but great the rest of the time.

I added a lockup switch to mine and use it a lot where I'm on and off the throttle in the hills. When it's time, get a built tranny.

 

With a 5" lift and 35's I would be interested to see how you are gonna get the trailer under it without overloading the trailers rear axle and maintain some bed to trailer clearance.

On my set up I put a lift on the trailer, lowered the back of the truck by pulling out the oem lift plates and now use a 285 tire. The trailer rides pretty level now and I have 7" clearance. I was running with 5.5" clearance and damaged my bed top with the trailer.

IMO on your tire size you will probably find towing in OD will not work well. I just pulled off a set of 295's that were 33.5 off my truck and found it towed in OD ok if you were doing 65 or more. Towing in "D" will sacrifice fuel mileage. I find 1800 rpm is a nice sweet spot for good towing mpg's.

You can play with the numbers here:
http://www.csgnetwork.com/multirpmcalc.html just scroll to the bottom and plug in .69 for the overdrive ratio and your 3.73's along with the speed you plan on running. Plug in 1.0 for a "D" ratio.

To get 1800 rpm in D you would be at 50 mph
To get 1800 rpm in OD you would be at 73 mph

 

I've got 315/70/17's, with 3.73's and a 48RE, and I don't often tow as heavy as you (my normal trailer/load totals about 6K), but on the occassions where I have pulled 10K plus to the Dunes, I haven't had any problems. On the long (boring) flat drive from Phoenix the truck holds OD just fine, only dropping out of it when going up the small grade about 25 miles east of Yuma. I've got just under 80000 miles on the truck now, well over half of them towing, and I haven't had the slightest hint of any issues with either the engine or the transmission.