atwowheelguy wrote:It is a choice. Do you want better performance when towing? Or better MPGs when empty?
With my '13 F150 3.5 EB 3.55 having just surpassed 100k miles, I started glancing at what's available these days. It is my only caged vehicle, I haul grandchildren, I occasionally need to squeeze it into a parking deck, and I tow a toy hauler that at various times weighs 6600-7200 lbs. Therefore the 3.5 EB Supercrew 5.5 ft. bed 145" wheelbase configuration is the one that best fits my needs.
I notice that for '17, only two axle ratios are available for that configuration with the 3.5 EB, the 3.15 and the 3.55. In '13 it was available with four axle ratios: 3.15, 3.31, 3.55 and 3.73. I ended up with a 3.55. The spread from 1st to 6th on the six speed is 604%. The spread from 1st to 10th on the ten speed is 744%.
I also note that the GCWR for my '13 3.55 six speed is 15,300 with a max trailer of 9,800, whereas the GCWR for the '17 3.15 ten speed is 15,800 with a max trailer of 10,700. The advantage is the 10 speed transmission in the '17, plus the '17 has a little more power. They have almost the exact same first gear final drive ratio.
My current wet and loaded camper weighs 6,640 (68% of 9,800 max trailer) which results in a GCW of 12,500 (82% of the GCWR) and the '13 tows it with no sweat. It's at 94% of GVWR, having used up 71% of its payload. I'll be looking at the 3.15 axle with the 10 speed for the next one to tow as well as the 3.55 six speed and get a little better highway mileage when not towing (19% fewer revs per mile in high gear). I give the Ford engineers an "attaboy" for this one.
