Alright guys I'm making a big trip at the end of the month and I'm trying to get my truck all squared away so I won't have any problems. Heading from CT to Florida with a 39' 5 wheel. I will be hauling the trailer a dozen times or so this year. When the trailers not on I do a little bit of highway driving but mostly just open roads.

I've pulled the trailer several times before but only with 33" tires.Once everything was going the truck ran great but took a while to get up to speed. I think lower gearing will really help especially with the 35s on. I'm looking at either the 4.30 or 4.56 gears and possibly a locker while its getting done as well (TrueTrac seems to be at a good price). I did some searching and it seems like most people with 35s would go with 4.30 but I think because I tow the 4.56 would be a better option.

I already have a DP tuner, AFE intake, MBRP exhaust, gauges, 6.0l intercooler + tranny cooler, and will be doing the TC mod, getting a BTS VB and an ITP tranny pan. Thanks guys!!!

 

4.30's will bring it closer to stock 3.73/stock tire combo feel. 4.56's will make it feel more like 4.10's/stock tire combo. The 4.56's with 35's will tow better, but fuel mileage unloaded will suffer more.

 

Good to hear, I was thinking along those lines but needed to check. 4.56 is what I'll go with. I need something to slow me down when I'm unloaded on the highway lol.

 

Here's a link to a chart I made with different tires and gear ratios that shows rpms at 70mph:

http://www.FTEs diesel forums.com/fo...ead.php?t=2896

 

Two things I regret. I got 4.56 instead of 4.30s. My trailer isnt that long, but its 11000-14000lbs depending on the day. I got a truetrac instead of a locker. If I had it to do over again, thats about all I'd change. My rpms at 75 are just stupid.

 

I installed 4.10's with my 35's. (I incereased tire size by 10 percent over stock and so 10 percent of 3.73's put me at 4.08 (4.10)). It seems to be back to stock. I also have a small 5'er and I hook a boat behind that and I would like to try 4.56 or 4.30 just to see. I may just try 285/75 next set of tires.

Long story short. 4.10's works for me, and milage is about 13mph pulling 3500# . And it pulls 5500# 5er up hills in OD without down shift, especially if I stay above 75mph.

your 39' weighs a lot more though. I bet 4.30 would be a good compromise mileage==power.

Good luck,

 

Two things to consider. with 35's, will your truck bed be too tall to fit under the 5ver and still pull level? Why not consider a US Gear underdrive with a 22% ratio change you can now have the gears to pull when you are hooked to the trailer, and the economy gears when running empty. dollar wise its not that much difference. and having the ability to "splitshift" between gears lets you fine tune your RPM's for your load. I love mine. And it works with manual or automatic trannys. Barney

 

I do alot of driving under 55ish, and i rarely go over 70 for cruising. I have 35's, and i was considering 4.56's. I drive a 07 with 4.30 and stock tires, and like the RPMs. Its alot quieter though so it will be a little different story in a louder truck.

 

I was worried about that at first. I've got a 3.5" lift (only add a leaf in the rear) and with 33s the truck sits almost as high in the back as my buddies stock '06 F350. I've got F350 blocks coming for the rear and with the 35s it'll raise it up another 2-2.5". My hitch is adjustable and can lower it down about 1.5", putting everything pretty close in align. Once I get the 35s in I will load the trailer on and see how she looks.

This underdrive unit is definitely something I'd be interested in getting. I started reading up on both the US gear and Gear Vendor units. The gear vender seems nice because it can shift under full throttle and has a 2 year warrenty. Are there any other units out there? I'd like to do it right the first time but wasn't expecting to spend more than $3k or so on the whole deal.

 

the GearVendor unit is availible as an overdrive only. Also you cannot use it with an Ebrake, in reverse, in 4 wheel dr or decellerating down steep hills. The US Gear dual range can be ordered as an overdrive or underdrive. it also can be used in any range, drive mode, and with exhaust brakes. I have owned both units and towed heavily with both. the US Gear is by far the better built unit. of course thats JMHO. The GV is a small automatic tranny. you must be at speeds abouve 25 mph in order for the internal pump to work. the US Gear unit is a small manual tranny. as long as you're moving it will shift with just the flip of a switch. As for shifting under full throttle, i found the GV banged so hard that I didn't feel comfortable doing it. The US Gear units requires just a slight lifting of the throttle, The unit should cost around 2500-3000.