What rear axle is better to order the 3:55 or the 4:10 on diesel engine.I will use the truck to pull a 15000 lb. FW. WHAT THE DIESEL CONSUMPTION DIFFERENCE BETWEEN THE TWO?

 

I have no experience with the fuel consumption difference but I would always go with the steepest gear offered when buying a vehicle for towing. So, 4.10 for sure.

 

I could be wrong but the 2016 Build & Price doesn't seem to allow 4.30 gears with the diesel on the 350 SRW. The 4.30 gears are available on the 450 DRW and 3.73 is available on the 350 DRW.

All I know is what I can come up with on the 2016 Build & Price page. I can't get to the 2017 Build & Price page at this time.

 

Depends on engine and rear wheel configuration. I'm assuming he's ordering a DRW 350 based on the two options he was choosing from. For 2017 the DRW 350 6.7 can be had with either 3.55's or 4.10's. For 2016 the DRW 350 6.7 could be had with 3.73's or 4.30's if the high capacity tow package was ordered. The 450 for 16 or 17 is always 4.30's.

The 2017 B&P is working for me via this link. http://www.shopus.ford.com/build/sup...9Q.592.66S.%5D

 

Towing 15k occasionally, I would think you would be fine with 3.55's. With the amount of torque these engines make, I don't think 4.10's would be necessary for that weight. I can't quantify the mpg difference, but am fairly certain you would see a perceptible difference on the highway unloaded, in favor of the 3.55's. While towing I doubt you'd see much difference in mpg between the two. If you are going to be towing 15k greater than 50% of the time, I could see going for the 4.10's.

Opinions will vary, but that is mine.

 

Thanks for the link. I'm not sure why I can't get to it when drilling down from the top level of Ford.com.

 

Go to trucks, future vehicles

 

Yes, that's how I drilled down earlier. Now it's working. WTF?

Correction: It is NOT working. Here is the URL I get: http://www.shop.ford.com/build/superduty/2017/#/select/

 

Did an rpm calc using a 33" tire ........ 3.55 gears @ 75 mph = 1816 rpm, 4.10 gears @ 75 mph = 2098 rpm. So you would be running 282 rpm more with the 4.10's .....not a big deal depending on where the 2017 engines sweet spot occurs.

 

The F350 has 245/75R17 tires which are 31.5" tall.

3.55 gear RPMs:
55: 6th gear: 1397, 5th gear: 1794, 4th gear: 2398
60: 6th gear: 1524, 5th gear: 1957, 4th gear: 2617
65: 6th gear: 1651, 5th gear: 2120, 4th gear: 2835
70: 6th gear: 1778, 5th gear: 2283, 4th gear: 3053
75: 6th gear: 1906, 5th gear: 2446, 4th gear: too high

4.10 gear RPMs:
55: 6th gear: 1614, 5th gear: 2072, 4th gear: 2770
60: 6th gear: 1761, 5th gear: 2260, 4th gear: 3022
65: 6th gear: 1907, 5th gear: 2448, 4th gear: too high
70: 6th gear: 2054, 5th gear: 2637, 4th gear: too high
75: 6th gear: 2201, 5th gear: 2825, 4th gear: too high

With 2800 RPMs for maximum power, the 4.10 will climb its best at ~55 MPH (4th) and ~75 MPH (5th); the 3.55 will climb its best at ~65 MPH in 4th.

The best axle ratio if you're towing heavy is the one the will give you the best power at the speeds you climb the big hills. The 3.55 will do relatively poorly at 70 MPH - 75 MPH as you are too fast for 4th, and 5th is well below the maximum power point. The 4.10's relative poor-band is at 60-65 MPH - too fast for 4th and well below the power band in 5th. It really just depends on what speed you want to tow. If I was getting the F350 dually, the 3.55 would be my choice as it is best at the east coast highway speeds (65 MPH).

For the truck I'm planning to get (3.55 SRW on the 20" tires)...
3.55 gear RPMs:
55: 6th gear: 1291, 5th gear: 1656, 4th gear: 2215
60: 6th gear: 1408, 5th gear: 1807, 4th gear: 2416
65: 6th gear: 1525, 5th gear: 1958, 4th gear: 2618
70: 6th gear: 1642, 5th gear: 2108, 4th gear: 2819
75: 6th gear: 1760, 5th gear: 2259, 4th gear: 3021
My hill climbing sweet spot will be 65-70 MPH - perfect. My relatively poor band will be 55-60 MPH, but just below 55 MPH works in 3rd if needed.

The 3.31, 20" tire sweet-spot is at 55 MPH (2730 RPMs in 4th) and 75 MPH (2816 RPMs in 5th)

 

Great breakdown using the accurate tire info (31.5" tall). I ordered 3.55's with my '17 dually. In addition to towing, I end up doing a lot of empty driving. Over 2k RPM going 75mph down the highway is not what I want. That means more engine wear and higher fuel consumption.

 

I don't have personal experience with the 6.7, but my experience with the 7.3, 6.0, and (to a lesser extent) the 6.4 has been that above 2,000 rpm the fuel mileage starts dropping like a rock.

 

I think this is one area a transmission with extra gears (10 speed) might come in very handy...allow a short final drive but with lots of overdrives for highway running.

 

Thank everybody for the info I will change the order to 3.55 .

 

x2. NGL - was a bit disappointed to only hear 6 speeds on the 2017 SDs. The driveability is *so* much better with 8.