Re: [VAC] Towing with a Ford manual transmission

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

Sorry, Phillip your option doesn't compute. Starting from the 3500 pound
factory rating with the 3.55 axle or 7800 pounds GCW, the thrust is
proportional to the gear ratio, so a 3.73 axle just gives 8195 pounds
GCW, or 3865 pounds towing capacity.

I can't find (at Firestone or Goodyear) LT235/70R16 tires to know their
dimensions. The factory standard tires are P235/70R16 which might be the
same size.

A 3.73 axle isn't enough to make second gear pull like an old fashioned
three speed transmission first gear to make first gear into more of a
granny gear for trailering only. It takes at least 4.1 in the axle to
accomplish that.

3865 might be almost enough for my '68 Caravele but it would be
marginal. For my farming applications it wouldn't be enough to handle
5000 pounds of empty gravity boxes. I'm spoiled, my previous ford truck
had a 6.5:1 first gear and wasn't bothered with 7000 pounds behind it.
Though it got overly exciting getting that much stopped without wagon
brakes!

The stock P235/70R16 tires are rated at a load of 1804 pounds. Goodyear
makes a P255/50R16, 26" diameter with 1687 pound load rating, Eagle
GT+4. The OD tire in my scheme, LT235/85R16 at 31.8" OD is rated at 3042
pounds load. At ordinary half ton truck loads it should last a long
time. It might be necessary to go to a wider rim with the really low
profile tires to have adequate load rating, but they suffer from loss of
clearance from axle to ground.

I'm glad you noticed enough to comment.

Gerald J.