On rear-wheel-drive vehicles, rear-axle ratio is an important part of a successful towing equation. It is expressed as a ratio between the driveshaft revolutions per minute and the rear axle's revolutions per minute. It is always given as a numerical expression like 4.1:1. This means the small pinion gear at the end of the drive shaft must rotate 4.1 times for every single rotation of the rear axle.
Each rear-axle ratio in the spectrum of those offered has a plus and minus. A ratio that is "low" in the number of drive shaft rotations for every axle rotation results in lower engine rpm and in better fuel economy, longer engine life and quieter running. But it won't be good for quick acceleration, climbing grades, carrying loads or pulling a trailer.
A "high" ratio, one with a high number of drive shaft turns like the 4.1:1 example above, is better for quick acceleration, climbing grades, carrying loads or pulling a trailer. However, it results in lower fuel economy and is noisier when running at high vehicle speeds.
The ideal axle ratio for your trailer towing will be a compromise. You want a ratio that will enable your Dodge vehicle to pull your trailer with the engine operating closest to its optimal power range - where peak torque and peak horsepower meet on the engine power curve chart. This maximizes power, efficiency and fuel economy.
But that ideal ratio won't be as good when you're not pulling a trailer. So you want a ratio that will give you good trailer towing power without handicapping your non-towing performance too severely. Heavy commercial trailer towing users aren't too concerned about this compromise because their vehicles are towing more often than not.
To determine what your best rear axle ratio choice may be, you'll have to do some trailer towing math as explained in the next section. Also, consult your Dodge dealer for assistance.