3.31 Gears

[scottyb]

I was wondering if anybody is driving a 6.7L with 3.31 gears? The tow ratings give it the same towing capacity as the 3.55's. My wife is about to replace her car and thinks she would like to go back to a F250. She is no stranger to diesels and has previously driven a F250 and an Excursion. I was just thinking the 3.31 might get a little better mileage since she will never tow anything with it. Any thoughts?

 

[jnbhobe]

I think 3.31 gears would be fine in the flatlands if your not towing and you can stay in 6th gear.

 

[BarneyFife]

If she's getting a big F250 for just driving around town, I would insist on 3.31 gears. I'd almost wish they made 3.00 gears for a daily driver like that.

 

[MTPockets]

We have the 3.31 ratio and have no problems, even in mountains... Our Big Horn scale weight fully loaded was 13,860 lbs and the truck fully loaded was 8640 ...... My next truck will be a dually, but for now, this one tows great and is level when hooked up.... If she's not towing, that truck has a lot of scat.... she'll be pulling away from everything on the road.

 

[dbbls59]

Fords 3.31 and 3.55 come out the same when the tire size is taken into account. That is why the tow rating is the same.

 

[rgwilliams69]

I just moved from 3.55 to 3.73 from a F250 SRW to F350 DRW. Can definitely tell a difference in driving and a difference in mileage (both from the lie-o-meter and calculated). My truck is still young yet (< 3000 miles) but I don't think I will see the same 20+ non-towing MGP I saw on the 3.55 F250 SRW. Since I do not do a lot of mountain driving wish I could have had an option for the 3.55 or lower. Current towing experience stays firmly locked in 6th at highway speeds even in hilly terrain, might be a little bit of overkill. And that is pulling the 18k Cyclone 4100 King.

 

[scottyb]

I found this on a SuperDutyDiesel.com.

Here's some numbers for you presuming 34" tires or 275/65/20 and a 3.31 rear

***************************************
Gear MPH/1000 MPH @2000 MPH @3500
***************************************
1 7.72 15 27
2 13.20 26 46
3 20.15 40 71
4 26.64 53 93
5 35.62 71 125
6 45.72 91 160

same tires w/ 3.55

***************************************
Gear MPH/1000 MPH @2000 MPH @3500
***************************************
1 7.19 14 25
2 12.31 25 43
3 18.79 38 66
4 24.84 50 87
5 33.21 66 116
6 42.63 85 149

and finally 3.73 gears
***************************************
Gear MPH/1000 MPH @2000 MPH @3500
***************************************
1 6.85 14 24
2 11.72 23 41
3 17.88 36 63
4 23.64 47 83
5 31.61 63 111
6 40.57 81 142

Using these numbers I come up with; at 70 mph;
3.31 1531 rpm
3.55 1642 rpm
3.73 1725 rpm

 

[rgwilliams69]

My 2012 F350 DRW (3.73 rear end) runs LT245/75/R17 tires and I think I thought I turned around 2000 rpm at 70 mph, I'll check it again today when I'm out. Also full disclosure, on my 2011 F250 the speedometer was about 2-3 mph slower (than actual travel) and I think I am seeing the same thing with this truck - gonna have my neighbor radar me to check, but that might make a difference also. I cannot remember what size tires I had on the F250 but it seemed like I was closer to 1500/1600 rpm at 70 mph in that truck (3.55 rear end).

 

[BarneyFife]

My 2012 F350 DRW (3.73 rear end) runs LT245/75/R17 tires and I think I thought I turned around 2000 rpm at 70 mph, I'll check it again today when I'm out. Also full disclosure, on my 2011 F250 the speedometer was about 2-3 mph slower (than actual travel) and I think I am seeing the same thing with this truck - gonna have my neighbor radar me to check, but that might make a difference also. I cannot remember what size tires I had on the F250 but it seemed like I was closer to 1500/1600 rpm at 70 mph in that truck (3.55 rear end).

That's probably about right. My 4.30 rear end has me turning around 2200-2300 rpms at 70 mph.

 

[MTPockets]

I'm trying to find where I saw it, but when I ordered my F350 w/3.31 gears, I got the 18" wheels..... With 20" wheels the literature did change (lower) the tow ratings.

 

[rgwilliams69]

I asked for 3.31 on my DRW but they told me it wasn't an option. Just on the SRW model I think can you get lower than 3.73.

 

[lwmcguir]

You really don't need the low ratio unless you are towing something heavier than a HL product. The new high torque diesels can handle the 3:55 just fine. All the lower ratio does is wear out your engine faster.

 

[rgwilliams69]

And just drove to town, looks like I'm turning about 1850/1900 at 70 mph. A little less than what I was thinking now that I paid attention to it.

 

[scottyb]

They found a truck spec'd like we wanted. It has 3.55 gears, so that's what we have. I probably would have to order one to get 3.31 gears. Seems like everything on the lots is 3.55. My wife is happy to be back in a pickup again. It looks black but it is Kodiak Brown. It is the darkest brown I have ever seen.

 

[rgwilliams69]

They found a truck spec'd like we wanted. It has 3.55 gears, so that's what we have. I probably would have to order one to get 3.31 gears. Seems like everything on the lots is 3.55. My wife is happy to be back in a pickup again. It looks black but it is Kodiak Brown. It is the darkest brown I have ever seen.

Beautiful truck - I really like that way the two-tone looks with that color! I wish I had my 3.55 gears back, but 3.73 was the lowest I could get on the DRW. My F250 CC SRW 3.55 towed like a dream with my last rig at about 15,500 pounds loaded. Enjoy your truck!

 

[scottyb]

Beautiful truck - I really like that way the two-tone looks with that color! I wish I had my 3.55 gears back, but 3.73 was the lowest I could get on the DRW. My F250 CC SRW 3.55 towed like a dream with my last rig at about 15,500 pounds loaded. Enjoy your truck!

Thanks. I'm just glad to have her back in a truck again. Do you really think you would like the 3.55's pulling the 4100?

 

[rgwilliams69]

I actually took a test tow with the Cyclone on the F250 before I bought the Cyclone and new F350. Towed just fine, airbags kept everything level. Tested on 2 lane, city streets, and interstate up to 70 mpg and even with the on-ramp being an upgrade climb had great acceleration. Did some heavy braking tests also. My friend riding along who is part-owner of the RV dealership couldn't believe that the F250 did such a great job towing such a huge rig. However as I sat down to calculate the weights in detail the F250 was over on several factors, including payload, rear axle, GCVR, etc. So although it appeared to me it would do the job easily I decided for safety's sake (and legal reasons) to upgrade the truck to the F350 DRW. F250 had the 3.55, so to me that says if I had the F350 with 3.55 I could expect the same type of performance.

 

[scottyb]

Interesting. My 3500 is an late 07 and has 3.73's. I know they have boosted torque and HP a bunch since then. It did really well until I hit the mountains in AZ. The water teperature climbed to 230 until the clutch fan kicked in, on each steep ascent. Downhill was in 2nd gear since there's no exhaust brakes on it. I was seriously considering a F450 with 4.30's, but that would be overkill for a daily driver. I have settled on a F350 DRW and looks like we are all stuck with 3.73's.

 

[rgwilliams69]

Well I can certainly say my test tow didn't include any aggressive grades here in Central Illinois. However during the drive no issues at all with engine or trans temps. We do most of our towing in the Midwest so the only thing we consistently deal with is wind, which always seems to be in my face whether I'm traveling North, South, East, or West. Just not sure how that works... As you say a moot point now though as 3.73 is where we live. Feels like I might give up a little mileage here, but when I do head to the Rockies or Smokies at least things should work well. I'll probably be putting another 10-12k on chasing the races and fish this year (hopefully starting in February) and we will see how the F250 compares to the F350 over the full season. But of course I'm pulling a coach now that is 2,500 pounds heavier than the last as well.

 

[NWILSON]

Just wondering how much the axle ratio affects the weight numbers on the Ford.
The 2012 Dodge DRW Laramie 3500 Max Towing goes from 8,900 w/3.42 then 12,900 w/3.73 and 19,100 w/4.10