Axle Ratio and tow rating

RoyB wrote:
We selected the middle ratio for us...

The 4:10 give you most towing weights and least fuel mileage
The 3:73 gives the best of both worlds for towing weights and fuel mileage
The 3:55 gives least towing weights and best fuel mileage.

Those were the options I have on my 2010 FORD TRUCK. I notice the lowest 3:55 is not offered on the newer trucks now.

Roy Ken

This makes some invalid assumptions, namely that the around town driving is going to improve with taller gears, which it will not, and that when towing the taller gears will provide better fuel economy and they will not. The second point may be less obvious but big rigs that fight to gain an extra few percent in MPG will use transmissions that provide 1:1 gears when carrying a load. The overdrive helps MPG only when the truck has an empty bed or trailer(s).

A lot of assumptions are based on the old 4-speed transmissions which had a 1:1 gearing for 4th speed. Most tow vehicles today have 6-speed or even 8-speed transmissions and so have 2 or even 3 overdrive gears.

The very tall gearing does help with the EPA fuel economy highway estimate figures which are based on testing done indoors. This is what matters the most to the truck and SUV manufacturers who need to meet federal CAFE standards while selling as many large, heavy, fuel inefficient vehicles as possible as these are also far and away the most profitable. The average truck/SUV sold in the USA provides a profit to the manufacturer of more than $10,000. Only the drug and tobacco companies do better than that.

The taller the gears the more load is placed on the engine's main bearings, on the transmission, and on the drive shaft and related bearings. This is why the gears affect the towing capacity of a vehicle.

Another consideration that gets overlooked is the 20 to 55 MPH time for a vehicle with even 50% of its rated tow load. That number is going to change considerably with taller gears and it will take more time and more "runway" to get up to the speed needed to safely merge with highway traffic. For this reason alone I would never buy a vehicle to tow with a gas engine unless it had 4.10 or lower gears (as with the Toyota trucks and the Ford F-450 pickup).