Gear Ratio Notes

Just a place to park by notes on truck gear ratio. I was going to write a blog post about it.  But – it’s boring.

Last updated 4/8/18

How I’m handling gear ratio: Should I plan to get a truck with 20% more towing capacity than the heaviest trailer I’m considering? I’ll just go with whatever the engineers decided upon as the best overall gear ratio, based on the tow ratings. So, if the heaviest trailer I’m considering is 17,500 pounds and I add 20% I’ll need a truck rated at 21,000 pounds. AND the same or better rated hitch to go with it. In the Ford F350 dually either the 3.55 or 4.10 gear ration will handle the 21,000 pounds. In the Ram 3500 it requires 4.10 gears with their Chrysler 68RFE transmission or better yet, get the Asian transmission where the 3.73 or 4.10 gear ration will easily handle 21,000 pounds. One note regarding the Ram truck. You get the high output Cummins engine when you select the Asian transmission. The Cummins that comes with the 68RFE transmission has less horse power and torque ratings. And the Asian is reportedly a much smoother shift and cooler running transmission than the 68RFE. SEE my notes on gear ratio.
• Or, some say just don’t exceed the trucks capacity as the truck is already designed to safely tow up to a specific weight.
• Or, some say you want the extra 20% for time you are in the mountains.
• Or, some say the increased capacity makes for a more pleasurable drive such as for those times you need to merge into traffic by accelerating.
• Or, some say get a truck that can handle more in case you upgrade your trailer.
• Or, some say get 50% more truck than you need.
• Or, some say when you drive into high winds, especially with a full profile fifth wheel, you will appreciate having the extra tow capacity.
• And finally, some say set the truck up for towing with the best engine, transmission and the 4.10 gear ratio.

PS, don’t forget about cargo capacity ratings. If the pin weight of your fifth wheel is 20% of the total weight, then for a 17,500-pound trailer the pin weight when the trailer is loaded is 3,500 pounds. To that weight add fuel, cargo and people. Not much of an issue for the Rams and Ford dually. While Chevy/GMC has overall less cargo capacity you might be extra careful when equipping their trucks.
B&W Hitch has a net page on their website to figure out what the tow ratings are for individual trucks. Of course, you can also surf the web to find the manufactures charts. Our go to RV Tow Check if you really want to play with the numbers.

All this is most important to me because we are buying the truck before the trailer and I’d hate to make any mistakes. And that includes getting the right options such as fifth wheel prep on the truck which includes the puck systems that are pre-installed for hitches that use puck systems. These systems are a series of holes in the truck bed in which the hitch is mounted, making it much easier to remove the hitch when you need to haul stuff.

Gear ratio for truck: Transmission and Axle Ratio: Both can change a trucks capacity, base weight and more. How do you pick the best for your driving conditions? I’ll probably just go with the manufacturer’s suggested for whatever tow rating can handle 19,500 pounds with a little safety margin.

Here is a decent article on axle ratios to include points to consider.

Here are the questions you have to answer to choose a gear ratio: (answers for my situation are in red as of 4/8/18)

o What is the target top-end road speed for the truck? 65 because I like to pull trailers five under the speed limit so others pass me so I don’t have to worry as much about someone being in my blind spot.

o Will the truck operate primarily on flat or hilly terrain? Mixed

o Will the truck pull a trailer? If so, what size and weight? What percentage of the time? Max gross weight trailer for my top six is 17,900 pounds. But have looked at ones as high at 19,500 pounds which are out of my price range if bought new. One, closer to my price range but not in my top six is at 18,000 gross. The other top five are at 16,500 and under. I need to take a look at what average annual miles people have been towing vs when using the truck as their daily driver. I could see someday having a second vehicle for a daily once the truck gets older and we are not moving pulling the trailer as much.

o Will the truck operate off-road? If so, what percentage of time? What type of surface? What speed range will the truck travel in those conditions? Not enough off-road that this is a consideration for me.

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