Ask TFLtruck: Ford F350 Dually – Which Rear Axle is Best to Tow a Camper Across Country?

2018 ford f350 super duty
2018 Ford Super Duty (photo: Ford)

Which rear axle ratio is best for towing a large camper trailer across the country?

Fred writes:

I am looking to get a 2019 Ford F350 dually. What rear axle ratio would be best for a large 5th wheel camper cross country trip?

The new Super Duty diesel comes with three rear axle ratios: 3.55, 4.10, and a 4.30. Take a look at the Ford’s towing guide chart below. The higher the numerical number of the ratio, the truck is said to have “lower gearing”. Having a 4.10 rear axle ratio means the drive-shaft spins 4.1 times per one revolution of the axle shaft that is going to the wheel.

Truck makers are able to rate the trucks at a higher towing capacity with lower gearing. The maximum towing for the Super Duty with a 6.7L Power Stroke diesel V8 and a 3.55 axle is 27,300 lbs. The rating goes up to 31,800 lbs with a 4.10 axle, and up to 32,500 lbs with 4.30 gearing.

Lower gearing also means the truck is able to get off the line a little better and negotiate steep mountain passes with a little more ease. On the flip side, the lower axle ratio takes down your fuel economy. The engine has to work a little harder to move the same distance.

A gross combined weight rating of a large 5th wheel camper trailer is around 20,000 lbs. This is a weight of a fully loaded trailer. A F350 or F450 dually are required to carry so much tongue weight (likely over 4,000 lbs of tongue weight). However, having a 4.10 rear axle is not a must for a 20,000 lbs trailer. The 3.55 can get the job done and provide a little better fuel economy down the road. If you do want a little extra oomph to climb and descend the Rocky Mountains, then go with the 4.10.

If you want to know more about towing heavy trailers with the latest 1-ton dually trucks, check out this video where we measure fuel economy on all three newest diesels.