Gear ratio confusion - RV-Dreams Community Forum

igotjam · RV-Dreams Family Member

Gear ratio confusion

EggerMar · RV-Dreams Family Member

I'm looking at the Ford F350 Diesel Crew Cab 4x4 DRW 2013 truck with an 8 foot bed. Planning on towing a 5th wheel trailer with 12,400 lbs dry weight. On the "Build your own" website, they are showing the following options for gear ratios:

3.31 Electronic locking axel ratio

3.31 Non limited slip axel ratio

3.55 Electronic locking axel ratio

3.55 Non limited slip axel ratio

3.73 Electronic locking axel ratio

3.73 Non limited slip axel ratio

4.30 Electronic locking axel ratio

4.30 Limited slip axel ratio

Any advise as to which of these options would be the best? Planning on being "almost" fulltimers 6-8 months of the year traveling around the country staying a few weeks here and a few weeks there before moving on.

Thanks .... all info appreciated as this stuff is like a foreign language to me

Marilyn

Terry and Jo · RV-Dreams Family Member

Marilyn,

I am not one to speak really knowledgeably about the Electronic Locking or Non-Limited slip, so I won't even address that part of the description. However, with regards to the numbers, the higher number (4:30) is a lower ration than the lower number (3.73).

What that means is that the 4:30 will tow better, but at the expense of fuel economy. So, if you want a rear differential that will tow better on mountain passes or long grades, the higher number is the way to go. If you want more fuel economy, but at the expense of towing power, you want the lower number.

So in essence, depending on the weight that you think you will be towing, I would go no less than a 3:73 rear axle. Now, someone else will have to address the "locking" issues.

Terry

Bill and Linda · RV-Dreams Family Member

EggerMar wrote:
Thanks everyone . That info helped greatly. Just seemed confusing because they charge a lot less for the 4.30 than the 3.31. Unfortunatly I don't feel confortable just trusting what the saleman says because they all seem to say something different.

Marilyn

Marilyn:

Let me add another point of information and perspective about the gear ratios in the “rear end” beyond what the saleman might be saying.

Absolutely true that a higher number, such as 4.1 as opposed to 3.6 is a stronger towing gear ratio, but ONLY in the same truck with exactly the same tire size and transmission and engine configuration.

Ford, Dodge and Chevy, for example, use different tire sizes and transmissions. So the rear end ratio numbers can be confusing as to what ratio is really needed for a particular job or application – such as towing or not towing. It is the same even within the same brand. For example, it is possible that a gas F-350 used for towing may need a much higher rear end ratio – such as a 4.3 – where a diesel, to tow the exact same weight, might need only a 4.1 or 3.8. I just use examples here, not specific ratios. You must consult the specification for the specific truck.

There is no need to get a really high rear end ratio on, for example only, an F-250 diesel if all you’re going to pull is a 10,000 lb Airstream. It is a huge waste of fuel, especially when driving the truck solo as you can end of getting 8 MPG towing AND driving solo if you choose too high a ratio that is not necessary.

Likewise across brands, Chevy diesels have 3.73 or so rear ends. That’s the highest needed for towing the same weight as a Ford that may have numbers in the 4.2 range and up. That’s because there are difference in the two brand’s transmission gears and they need different rear end numbers to pull the same weight due to these differences. Neither is “better;” just a different design. Review the towing specifications for the trucks and you’ll see what I mean.

All that said, and within reason, don’t get a higher rear end ratio than is required to pull your trailer. A bit of head room is fine in the selection and I recommend it. Don’t push it right against the spec or you will be disappointed. But choose the rear end ratio based on your specific application for the best performance and fuel economy just like the big semis do when they are built for specific types of service.. That’s why there are options.

Hope this helps a bit.

Bill

-- Edited by Bill and Linda on Monday 25th of March 2013 06:58:47 AM

Lonney Wade · RV-Dreams Family Member

Lonney Wade wrote:
If I may, could I straighten the gear ratio confusion up with the 3.73 Electronic locking axle ratio, it is a very good gear ratio, like they said the 3.73 is better on gas and the 4.30 has more pulling power, the Ford diesel has all the power to pull either gear ratio, all the electronic locking axle means is you will have positive traction which you can turn it on or off by the push of a button, what 3.73 gear ratio means is the drive shaft will turn 3.73 or about 3 3/4 turns to one turn of the wheel or the tire.
In my younger years I was in racing for 15 years, the last 2 years I was in top fuel sand drag racing with a 10/71 blower, we ran a Ford 9in all built up and we played with different gear ratios like 6.20, 6.50 gears and so on, the 4.30 gears will have more pulling power at take off but will run higher RPMs at highway speed and burn more diesel fuel in the long run, it's a matter of what you like, hope this helps.

Lonney

EggerMar · RV-Dreams Family Member

Thanks everyone . That info helped greatly. Just seemed confusing because they charge a lot less for the 4.30 than the 3.31. Unfortunatly I don't feel confortable just trusting what the saleman says because they all seem to say something different.

Marilyn

VanMar · RV-Dreams Family Member

EggerMar wrote:
I'm looking at the Ford F350 Diesel Crew Cab 4x4 DRW 2013 truck with an 8 foot bed. Planning on towing a 5th wheel trailer with 12,400 lbs dry weight. On the "Build your own" website, they are showing the following options for gear ratios:

Marilyn,

In my research, I have looked at the Ford and found the following: If you get DRW with the diesel, you have the choice of one ratio, the 3.73. You can only get the 3.31 with SRWs. The 4.30 is for trucks with the GAS engine. GM is the same way-- DRW with the diesel and 3.73 is the only choice. If you're towing close to the max and in the mountains a lot, you could go to a driveline shop and have a 4.30 swapped in if you wanted.

Hope this narrows your choices and removes some of the confusion.

Vance

Terry and Jo · RV-Dreams Family Member

One correction to Vance's comment. While it is a bigger truck, the F450 diesel 4X4 comes with the 4:30 rear axle ratio, so the comment about 4:30 rear differentials being for gas engines isn't "entirely" true. However, according to the 2013 brochure, only the F450 has the 4:30.

Terry

dewwood · RV-Dreams Family Member

If you are specing out your vehicle, normally when you choose the diesel engine it will automatically select the proper rear end to go with the transmission. The only option is positve traction which locks up the rear wheels when one start to slip. Like others have said the 3:73 are what most manufacturers go with. Good luck with your research!

EggerMar · RV-Dreams Family Member

Thanks again for all the input everyone. Vance and Terry.... your last comments cleared up a lot for me. Like I said,.... I have a lot more faith in the opinions of this forum than for most of the sales folks I've talked to. One tells ya one thing and another something different.

Marilyn