[VAC] Towing with a Ford manual transmission

["Dr. Gerald N. Johnson, P.E." <geraldj@xxxxxxxx>]

The F-150 5 speed manual transmission and standard axle is poor for
towing with a rating of only 2200 pounds with the v-6 or 4.6L V-8. But I
bought one any.

Here's the status of my computations applicable for certain to 1997
through 2000 models:
With the 3.08 axle the Gross Combination Weight is 6500 pounds.
With the 3.55 axle the GCW is 7800 pounds.
With an aftermarket 4.10 axle the GCW is 9008 pounds using the standard
tires.
With an aftermarket 4.56 axle the GCW is 10,020 pounds with the standard
tires.

The empty truck is about 4300 pounds so the trailer weights are 2200,
3500, 4700, and 5700 pounds.

The overall drive ratios in overdrive are: 2.34, 2.70, 3.11, 3.47 so the
effect of the 4.1 axle is like driving in 4th gear on the 3.08 axle.

I've decided to go with the 4.10 axle for the 4700 pound rating. Then if
that's a little weak, I'll change the back tires from the standard
P235/60R16 that are 29.1 inches diameter to something smaller. Maybe as
extreme as 26" diameter (at the sacrifice of 1.5" ground clearance)
(P255/50R16) to get the same GCW thrust rating as with the 4.56 axle.

If I have a yearning for better gas mileage when not towing I might
swing for a pair of 31.8" tires (LT235/85R16) to give the effect of a
3.77 rear axle, at the cost of towing capacity down to 4000 pounds.

Changing tires is a lot easier than changing axle gears and with this
combination with the speedometer calibrated for the 4.10 gears and
standard tires the errors would be 10 or 11% for the pulling or
overdrive tires.

There is an electronic speedometer box available for the computer based
trucks that may be easily changed when changing or rotating the tires. I
might just own four tires, two of each extreme size, and swap them front
to rear when changing modes. In that situation I might want to carry two
spares under the topper.

If ground clearance is not a requirement, I believe there are tires that
would bolt on (P205/40R16) that would have the same effect with the
original 3.08 axle ratio as going to at least a 4.30 axle an the
original gears. There's not room to go to smaller than 16" rims on the
fronts though there is room on the back brake drums. With the truly
extreme tires, it probably would be handy to go to an adjustable height
air suspension at least on the rear to level up the frame. Those parts
exist for kids trucks and would work here.

I figure traction bars will be needed to keep from winding up the rear
springs.

Gerald