I am looking at a 2012 F350 6.7 with 20's

What I am not so sure of is the 355 GS Ratio for towing. How well will that hold up with a 14K load?



3.55 AXLE RATIO W/ELECTRONIC LOCKING REAR AXLE,FX4 OFF ROAD PKG,(4) UPFITTER SWITCHES

I did a little searching
https://www.ford-trucks.com/forums/1...do-i-need.html
https://www.ford-trucks.com/forums/1...-to-6-7-a.html

But would like to hear some thoughts on durability.

Thanks

EDIT ADD ON
Minimum off roading and I dont really have plans to change the tire size right now. I was leaning toward a 373 but I see a lot of the SRW's have the 355 and I would prefer the SRW over the DRW's

 

can't speak to durability yet as I only have 7k on a 250 6.7 with 20's and 3.55 eld,
but the 2k+ towing miles @ 23k gcw has been great !

and faster than I want in as much as it isn't taxing the engine....just loping along with peak torque @ 1600 rpm's

 

let me just put in my 2 cents. A diesel really does not notice gear change as much as a gasser would. Does not matter if you have 16's 17's 18's or 20's because you have not changed the outer diameter, only the sidewall distance from the rim to tread.

A 32 inch tall tire is the same in a 18 or 20 inch rim. Or did I miss the question.....

 

Thanks
14 k is mt on my pull. So normally it runs about 21k or so. 38ft fith wheel.

My 96 7.3 does okay but its starting to wear and I dont want surprizes while towing. Still great truck it sports a 410 with some minor hp mods. Several yrs ago I had a higher gear ratio in another truck and I over taxed it. But the transmition was different back then and since then there have been several technical improvements so I really just dont have any idea on the 355 on performance, towing or durability and you know they will tell you about anything you want to hear to get you to buy.

So as mentioned before I really appreciate the comments, Thanks REPS sent

 

Another nice thing is the 6 speed auto over the older models, you will like that when towing.

 

No not really. Diesels is not the question. Its the durability of the 355 compared to 373 or 410 and towing.

 

Thats what I heard

So that should actually help the 355 durability. I would not want a 355 in my present rig. I would not mind a 373 in it. But I will keep that one. I am right on the edge of buying a new 2012 and just was wondering about that. Dont want to start hearing that whine after some mountain pulls.

Thanks oh and I did not mention it but I rep everyone on my thread replies. I appreciate the comments and heck there mine to give anyhow. Thanks

 

Reps are free!

 

EXACTLY

 

Hmmm just had a thought about putting a temp probe in there.

So basically if I get a 355 then I should stay with the same size tires. If I increase the tires circumfrence then actually I would in effect be lowering the gear ratio. If I get smaller tires I would (in effect) be increasing the gear ratio. 100 # of torque sent to either is only 18 on the difference between a 3.55 and a 3.73 so there is little significance in performance. The only difference I can think of would be RPMs and applied tourque which would vary the heat and the friction relative to the load. Since there would be more revolutions on the 355 vs 373 a ever so slight friction multiplier with the applied load to tourque I think that there is little to be concerned with.

So after all that gibberish lol. I guess there would be not too much difference in normal runs its only the hard applied torque from low rpms that may change the stress factors due to gear paterns and contact gear surface area.

Considering that; I guess my only concern would be friction and having enough surface contact to ensure equal distribution of load internally on the applied gear surface patern contact points. With the 6 speed that should spread that over a broader range than if it were a E4OD or the 5 speeds so the 6 spd transmision modifies the applied tourque values during normal driving conditions.

So to sum it up I think if I dont dog it on take offs I should not see any stress factors from routine driving and towing and if the heat load is constant the viscosity should remain consistant and I should be ok with a 355.

Does that sound about right? So I think my only concern now is on grades greater than 12 degrees and the applied force torque x load as it relates to total surface to surface contact in the gear and maintaining lubrication viscosity.

But I read where the max tow package compensate for this. Anyone have any info on a max tow package?

I will have to look into that. Heck I dont even know what that consist of or if its optional or not on 2012's SRW but I think a max tow package is related to a 3.73 gear ratio and some other components.

Sorry for the extending blabbing

 

Do you mind if I ask why you don't look into a DRW? They are after all meant to tug. I have the 3.55 but I have only hauled heavy. No towing. Personally I think you will be fine SRW with 3.55.

 

Thanks
I can not rep you now as I am on 24 hr jail time from the FTE gods for being too nice lol

But I will be back.

Well the DRW would actually be better if thats all I do with the truck but theres the draw backs with those for the fuel economy is generally 2 - 3 mpg less than the SRW. Extra tires to rotate, tighter parking spaces, in general but the main reason is the majority of the time I will not be towing with it. I will only tow for recreation so give it aout 3 trips per yr and thats about it.

I have really considered it though and I know I would really liek how it tows steady minimum sway and all.

Then we have the final straw that breaks the camels back. I would have to make my wife park her car out side so I could fit the DRW in the garage. HAAAAAAAAA HA HA HEE HEE HEE Whew!!! and thats not gonna happen. lol

 

I have 3.55 and tow my 15K thauler in the mountains. All I can say is WOW. World of difference from my 07 6.0L PSD. The gear ratio and tire sizes depend on which package you choose to outfit your truck with. The camper package and heavy front suspension are limited to 18 inch wheels with 3.55. You can look at the Ford truck body builder guide for wheel size and gear ratio options and limitations with different suspension packages. 3.55 are good middle of the road gears. I doubt you will notice much diff towing though with the 6.7 torque and HP between 3.XX ratio gears

 

Thanks Mr

Is that info on line somewhere. Looking at the sticker on the truck I am not sure whats what with that. So before buying I would like review those specs on line some where and then maybe scrutinize exactly what they are offing on the truck,

 

I have the PSD with 20s and 3.55, I pull a 32ft boat fully loaded is in the range of 13k to 14k, it tows with no struggles or problem. Just pulls like a beast.