Originally Posted by SierraHawk
Need another opinion related to tires: I am now running 285/75/16 tires (33" dia). A 275/70R16 is 31" high and has a 10.60" footprint. If I put these on, I would loose 2" in radius (1" in clearance). If I use a 275/70R16, would I notice any less strain on the engine while towing a 7000# trailer over steep mountain passes?
Smaller tires will help .
I assume from other posts that you have a 5.4 L and most likely the 4R75 transmission. Based on that, you will want to keep it above 2500 RPM when working it because that is where the peak torque is and maximum HP is reached at 4500 RPM. So if you drive below 2500 RPM climbing a big hill you will be wondering why your engine is struggling.
Stock tires and gearing with O/D shut off would put your RPM at 60 MPH @ 2527 with a 3.7 rear end and 2800 RPM with 4.1's. You don't have to drive that fast but notice how high the RPM is. The factory designed it that way for a reason.
With 31" tires, O/D shut off at 60 MPH the RPM is 2483 with 3.7's and 2750 with 4.1's. Close to stock.
With 33" tires, O/D shut off at 60 MPH the RPM is 2332 with 3.7's and 2584 with 4.1's.
Notice what the smaller tires do to your overall gearing, they lower it, rasing your RPM at a given speed. That is why the smaller tires will help you pull the big load. Higher RPM = power, it has nothing to do with the weight of the tires.
A 9000# SMB pulling a 7000# trailer is asking a lot from a 5.4L with 33" tires unless you have 4.56 rears. Maybe you could put it on stock tires when you tow and leave your gearing alone. Carry your big tires with you and put them on once you drop your trailer. Don't make the mistake that keeping engine RPM low is somehow taking it easy on the drivetrain. It isn't. Drive slow, keep the RPM up even if you have to drop another gear. Oh and don't forget to use your four way flashers going up hill.