I have ordered my 15 King Ranch. I am going to have a 5.0 in it, and am trying to figure out if I should keep the 3.73 gears I ordered it with, or change to 3.53.

I will be doing mostly city/highway driving, and plans are to get a boat(about 6000 lbs) in a couple years. I will be doing a leveling kit and running 34" or 35" tires on the truck.

From all the experience that has done the same thing, would you go with 3.55 or 3.73 gears? How has the gas mileage been? What about the pickup?

Thanks for all the help!

 

If you are putting bigger tires order it with whatever you want and get the dealer to put 4.10 in it. I have 35's on my 3,5 ecoboost and with the stock 3.55 it is a PIG on fuel. Its running so much boost all the time because of the lower rpm load that it is horrible. If i shift it to 5th and get the rpms up about 2-300 rpm the boost drops off to almost nothing and the fuel mileage indicator drops about 3-4 MPG. Stock tires i would throw the 3.73 in it. Gonna have my dealer swap the gears out in the next couple weeks. I actually debated going to a 4.56 but i think the 4.10 should be OK.

 

I would have said 3.55 all the way up until you said 35" tires. I think at that size, I'd go 3.73. That combo will probably bring your final gear ratio back close to what 3.55 and stock tires are. I have 3.55s in my 5.0 KR, and love them, but the biggest tire I'll run will probably be a 33" (MAYBE 34") someday in the far future. I do plan to get a boat of about the same size in the near future.

 

With 35" tires 4.10 is almost identical to having stock wheels and 3.55.

 

I'm not following this. A turbo is driven off exhaust gasses, and don't you get more boost at higher RPMs? Going to a 35" tire from a 32" w/ 3.55s should drop the RPMs by about 200 rpms, so wouldn't that keep you out of boost? What am I missing?

Looking at a Lariat w/ 3.55s that I'd like to put a 285/65-20 on (34.5"). I don't think 3.73s are an option w/ this combo. I'm also currently in a Chevy Avalanche 5.3L w/ 4.10s and 34.5" tires... You want to talk pig? I'm lucky if I see 12mpg.

Edit - Basically, What I was expecting was that a truck w/ 3.55s and 35" tires would drive similar to a truck w/ 3.31s and stock 32" tires. No?

 

The first basic is load=boost=power=more fuel.

 

Stick with the 3.73 for those tires.

 

^^^^THIS^^^^^

Lower rpm with bigger tires is creating more load. Therefore creating more boost. More boost = More fuel. A few hundred Rpm and the motor isn't working as hard. Less load = less boost = less fuel.

If you look back in the 11-14 forums their is a lot of people who have realized fuel mileage gains from going to the 4.10. Even in a stock tire size Truck.

 

I was getting 11.81 on my last trip. That's Canadian gallons too. Its the equivalent to 9.924MPG in the US. Hand calculated. Not the lieometer in the truck.

On my way home I drove the truck in 6th gear at 70MPH 1900RPM for 25 miles and was getting about 12MPG on the dash gauge. Boost gauge was around 1/3. Then i manually shifted it to 5th gear for 25 miles. Same speed and about 2250 RPM. Boost gauge was almost not registering. Dash was reading 16MPG after the reset. This road is approx. the same for about 150 miles. Not much change in elevation or hills etc. Also while in 6th the truck would downshift quite often to 5th. Obviously while in 5th it never budged. Boost gauge would creep up a little then back down on the hills. Just my experience with the higher rpm is all. I am swapping to 4.10. Don't 3.73 would be enough of a difference to warrant the swap.

 

Well from someone with exact experience to your scenario, I have lariat 3.5 Eco with 295/60/20 (34") and 3.55 gears and own a 24' bay boat when all said and done with boat motor trailer fuel gear pushing 5,500 to 6k. I have a level kit on and the boat is tongue heavy so I put on air bags to help. Truck pulls it fine and handles the tires fine with the 3.55 but if I had to do it again I would have gotten the 3.73's. So there is my answer.

Now not to steal your thread but it's related, will the 3.55 gears with 34" tires burn more fuel then 3.73 gears with the same, I know stock the 3.55 is more efficient but with the extra weight/size I'm wondering, I know it will help with get up and go for sure. It still gets it but I can tell I put the tires on for sure.