07 - ways to raise 4th gear rpm while towing
03-05-2017, 01:18 PM
#1
07 - ways to raise 4th gear rpm while towing
So I have been trying to figure this out. We use my 07 FX4 to tow our 28 foot camper. All loaded the total tow weight is probably close to 7000lbs. The truck has 285/65/18 Nitto Terra Grappler 10 ply tires on it and the 3.73 gears. The truck pulls the camper no problem. But I do notice a huge difference in mpg when I can tow in overdrive vs. 3rd gear. I have calculated trips with almost 3mpg difference when able to tow in overdrive.
I have a edge CS which I can put the tow mode on which raises the shift points but as far as I'm aware has no affect on final drive rpm.
The truck will easily pull the camper at 70mph in overdrive (4th) if doing 70mph and the converter stays locked. RPM is around 2400 at that speed. Drop to 60 mph and the truck wants to keep downshifting to 3rd as rpm drops to 1800 or less and obviously trans temps come up.
70mp wouldn't bother me but the speed limit is usually 60 anywhere around where I live or go camping plus that's a lot of weight to stop quick so I'd prefer to keep it down.
Now my question is....any way to effectively raise my final drive gear ratio? Gear swap to 3.90 or 4.10's?
if I went to a 275/70/18 how would that affect the situation?
Thoughts? I am just stuck towing in 3rd gear?
I have a edge CS which I can put the tow mode on which raises the shift points but as far as I'm aware has no affect on final drive rpm.
The truck will easily pull the camper at 70mph in overdrive (4th) if doing 70mph and the converter stays locked. RPM is around 2400 at that speed. Drop to 60 mph and the truck wants to keep downshifting to 3rd as rpm drops to 1800 or less and obviously trans temps come up.
70mp wouldn't bother me but the speed limit is usually 60 anywhere around where I live or go camping plus that's a lot of weight to stop quick so I'd prefer to keep it down.
Now my question is....any way to effectively raise my final drive gear ratio? Gear swap to 3.90 or 4.10's?
if I went to a 275/70/18 how would that affect the situation?
Thoughts? I am just stuck towing in 3rd gear?
03-05-2017, 01:55 PM
#2
Yes gearing would be the way to do it. You get a two fold effect of having better mechanical advantage while also raising the RPMs a little so you are deeper into the torque. That said I dont think a 3.90 is gunna do much at all. You may need to go 4.10 to even notice.
Other than that you would need to go to a smaller tire but without going WAY smaller you wont see much of a differnence. A 275/70R18 is a bigger tire than the 285/65/18. Its going to reduce your effective gear ratio even more. A narrower tire may help though as long as you keep it the same height or smaller.
Other than that you would need to go to a smaller tire but without going WAY smaller you wont see much of a differnence. A 275/70R18 is a bigger tire than the 285/65/18. Its going to reduce your effective gear ratio even more. A narrower tire may help though as long as you keep it the same height or smaller.