How to Keep Your Transmission Alive Off-Road

A modification for your modifications

When modifying your diesel truck it’s easy to get excited about changing the things that you can see – but easily neglect the things you can’t. In some cases this can cause some very costly issues down the road, and today we’re going to show you one of those not able to be seen by the naked eye.

In this instance we have a 2023 Ram Prospector XL that is made to dominate the backcountry. This truck is packed with all the accessories and upgrades to be able take you just about anywhere you need to go and even set up camp for a while! Coming off the lot with cut fenders which allow you to fit a 40” tire with only 3” of lift, massive bumpers, 16,500 lb. winch and a full camping set up, this tank of a truck appears to be ready to take you wherever you want to go.

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The issue here is what lies beneath the surface. While all of these options increase the trucks

backcountry capability, the weak point of the 68RFE is exploited due to the trucks shear weight and stock gearing. This overtime has completely smoked the transmission from the extra strain that is put on it with the off road upgrades this truck wields.

So what is the importance of gearing and why does it play such a crucial role in trucks that are running bigger tires, and especially in off-road settings? To understand this we need to dive into understanding gear ratios and their effects.

The differential gear ratio refers to how many times the driveshaft must rotate to turn the tires once. For example, a 3.73:1 ratio means the driveshaft turns 3.73 times for every one revolution of the tire. When you increase tire diameter, you increase the distance the vehicle travels per one full revolution. This increase effectively lowers your gear ratio, thus making it harder for your engine to move the vehicle, especially from a stop or under load.

Effects of Bigger Tires Without Regearing Axles:

Reduced Torque at the Tires.
Increased Stress on the Transmission
Reduced Fuel Economy
Speedometer Inaccuracy

Hindsight is 4:44
The truck manufacturer sets up the engine, transmission and axle gear ratio to work in harmony. This ensures that the engine can run at its optimal RPM ranges for efficient power production and it can then deliver that power to the ground. When you drastically change one of the output variables, there is going to be a negative effect in the chain. In this case, it was engine power and transmission reliability.

Curious on if a regear is right for you?
Example: Let’s say your truck has a 3.73:1 gear ratio with 32-inch tires. You upgrade to 40-inch tires.

Effective gear ratio = (Old tire diameter / New tire diameter) × Old gear ratio = (32 / 40) × 3.73 ≈ 2.98

You’ve gone from a 3.73 to a functional 2.98

By increasing the gear ratio to a 4.44 we are able to get the RPM range back up to a very close to stock range which the transmission would have loved. To better handle the constant heavy weight of this truck and the abuse it is put through, this is the time to upgrade the transmission that is going back in. In this case we went with a Randy’s Transmission Stage 2 68RFE. Once the work was completed, we saw our engine RPMs increase back up in to their efficiency range as well as being able to run in the higher gears on the Interstate. Less shifting and searching for gears. Lower transmission temperatures and a welcomed increase in fuel milage. In the back country settings this truck will feel much more comfortable in low-speed controlled crawl situations due to the increase it its power delivery.

Although there was no excitement of changes in appearance during this repair, the increases in drivability and driver confidence will certainly quench that thirst.