Rrear gear change

Now there is a loaded question! For starters it involves a little more information. Things like body style, tire size, terrain, frequency of in town vs highway driving AND personal preference!
 
The overall average gearing for most old Fords of the 30s/40s is the 3.78:1 ratio. A taller gear like a 3.54:1 would give higher speed with less engine rpm but the old 85HP has a harder time getting it up there on the heavier models. Some of those models came with 4.11:1 gearing so they get to 55 mph OK but the rpm is up there for anything above that. Columbia overdrive gives the best overall gearing but they are getting harder to source for the older models and they aren't cheep to purchase in good condition either.
 
My 46 business coupe has 4.11s, at 5o mph it is turning 2520 rpms. I can take off from a light in second gear almost effortlessly. I am putting 3,25s in soon. My merc powered 32 has 2.80s and is a pleasure to drive. Roads are different today, plus our fords dont have to do double duty when the tractor breaks down. Rich
 
I installed 3.78's (replacing 4.11's) in my '35 fordor sedan, with 85hp, 21 std engine, in 2013. I can cruise all day long at 60 to 65 mph. Had to downshift into 2nd a couple times coming over the Rockies.
 
Another sampling .... my '47 coupe has stock 59AB 100 hp, burns 87 octane, has a BW overdrive, 3.78 rear, and 15 inch Coker Classic bias ply tires. Engine turns abt 1900 rpm at 55 mph, abt 2300 rpm at 65 mph. Over varied country side and interstate terrain I prefer a "sweet spot" of 55 mph to have plenty of power reserve and to obtain about 16 mpg .
 
My little '37 21 stud turns over ok, its a very strong standard engine with a 39 toploader, 28 gearset, 3.78 rear and 7.50x16 tyres. in traffic every day no problems, don't even change out of top for some corners, that's in a 35 pickup.
 
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