[menmyjp]

Hey guys I'm new to the forum and looking to purchase my first diesel. I have researched many mixed reviews of the 3.31 vs. 3.55 and am still undecided.

The truck I'm looking at has 3.31 and the dealer has a set of 20'' factory wheels that he is willing to throw in. I know that to get the 20'' from the factory you have to have 3.55's but does any one have any experience with 3.31's with 20'' wheels and a large (33''-35'') all terrain tire.

Any feedback would be GREATLY APPRECIATED! THANKS

 

[JRoadDawg]

Hey guys I'm new to the forum and looking to purchase my first diesel. I have researched many mixed reviews of the 3.31 vs. 3.55 and am still undecided.

The truck I'm looking at has 3.31 and the dealer has a set of 20'' factory wheels that he is willing to throw in. I know that to get the 20'' from the factory you have to have 3.55's but does any one have any experience with 3.31's with 20'' wheels and a large (33''-35'') all terrain tire.

Any feedback would be GREATLY APPRECIATED! THANKS

It all depends on what you intend to use the truck for... If you intend to do heavy towing... pass on the 3.31 and 20 inch wheels. However, if it is only light towing or hauling... Go for it. Some have said that they do not like the low first gear in their trucks anyway. I have the 3.55 rear and 18 inch wheels. I like that combination but I am considering larger tires which will effect the final drive ratio. It really ends up with what you intend to do with the truck...

:5:

 

[00buck]

I'll throw what little I know in on the matter- the 3.31's with 18" wheels are turning low enough rpm's as it is, I'm afraid to go with bigger tires in fear of dropping the r's even further.
For instance, when turning 2000 rpm's in 6th the truck is going 86/87 mph's!
It's only doing ~1800 rpm's at 80mph.

Once again, pure speculation- the low RPM's I feel are the cause of my frequent regeneration cycles. (so far- under 100 miles per regen when not towing)

My friend has the 3.73's in his dually and his doesn't regen near as often as my truck does.

The regens are negating the better mileage benefit of the higher gears IMHO.

 

[00buck]

Wow, this forum is acting wierd- it won't let me edit the mistake ^.
It was 18" wheel.

As far as the low first gear concern goes- I don't even feel first in my truck with the 3.31's so maybe there is a benefit to the high gears after all.
I need to pay more attention to see how long it stays in 1st since I don't even feel it.

I'm usually in 3rd by the time I look at the dash.

 

[menmyjp]

Thanks for all the help. The regen is exactly what I'm worried about. I will primarily use the truck for light towing with occassional heavy towing and just thought the taller gears would be better MPG. I appreciate the input but I'm still not sure, I really would like to know of someone running this setup (3.31, 20'' w/ a 33-35 tire.)

If anyone has any other two cents I'd greatly appreciate it as well.

 

[Dak]

I really like my 18's and 3.55. I actually wish I could get 3.73 with a SRW.... But I do a lot of CITY driving, so better off the line then top end speed. Not that I can't run at 95 (the speed limiter) all day long if I needed to.

But I say drive it with the tires on it. I am not a fan of the 3.31 rear end, but I am old school and still like 3.73s or even 4.10's if I was going to put larger tires on it.

 

[Painted Horse]

The rim size isn't the important measurement, The diameter of the tire is., The OEM 20's come with a 34.x diameter tire. The 18" come with a 33.x diameter tire. If you step up to 20" rims and get 33" tires, You'd be the same as having the OEM 18's

 

[summitman6.7]

Give me a couple weeks to get good rerults, but I'm picking up my 2011 F350, crew/long on Saturday. It has 3.31's and I had a set of Rockstar 20's installed with the factory size 34" tire installed on it.

 

[jawarford1]

20's on with 3.31 gear

Give me a couple weeks to get good rerults, but I'm picking up my 2011 F350, crew/long on Saturday. It has 3.31's and I had a set of Rockstar 20's installed with the factory size 34" tire installed on it.

How do you like the 20's with the 3.31 gears ?

What kind of mpg's are you getting ?

 

[summitman6.7]

The 3.31's and 20's work great. I used the stock size with a Goodyear Duratrac tire. I've been seeing mpg's around a consistent 19 at 73mph on the highway, empty and no sacrifice with power. The only thing I'd MAYBE do different is go with a little taller tire.

 

[Painted Horse]

Running the 3.31s and the OEM 275/65r20 tire size is not much different than all guys with 3.55 who add aftermarket 35" tall tires. The OEM Michelin 275/65R20 tire is 34.1" tall. The 275/70r18 is 33.2" It's a 9/10ths of an inch increase in height for both upgrades.

This engine is designed to cruise in 6th gear at 1500-1600 rpm. If you are towing 13,000-16,000 lbs on a regular basis, I'd probably stay with the 3.55s. but if you are towing a smaller ski boat, atv trailer or tag along travel trailer at 6000-8000lbs. The 3.31s will do just fine with the 34" tires.

I'd be leary of putting on too tall of a tire and changing your cruise rpms to 1200-1300 rpms.

 

[summitman6.7]

I should have said, when i was thinking I MAYBE would go with a taller tire, I ment somthing closer to a 35" with a little more width.

I think it would lose a lot of power/trans shifting/MPG with something like a 37" and the 3.31's.

 

[ctire]

ok i am confused

331 or 355 gears my use is heavy pull 1/10 of the time 3/10 light pull then the rest of time no trailer just occasional load in the bed of 1000lbs or so. I am looking to buy and need someone's help. cause my 2009 f350 has crappy fuel mileage but will pull what ever i hook up to. I like that but i need better fuel milage mine is around 11 mpg to 12.6 at the best or is the new 2012 any better on fuel milage

 

[Hdslider]

331 or 355 gears my use is heavy pull 1/10 of the time 3/10 light pull then the rest of time no trailer just occasional load in the bed of 1000lbs or so. I am looking to buy and need someone's help. cause my 2009 f350 has crappy fuel mileage but will pull what ever i hook up to. I like that but i need better fuel milage mine is around 11 mpg to 12.6 at the best or is the new 2012 any better on fuel milage

I take this mpg stated is your pulling mpg,or is it empty? if thats empty the new truck does a heep better than that. If its your heavy towing mpg. your not far off from the new truck.

 

[Luke05]

331 or 355 gears my use is heavy pull 1/10 of the time 3/10 light pull then the rest of time no trailer just occasional load in the bed of 1000lbs or so. I am looking to buy and need someone's help. cause my 2009 f350 has crappy fuel mileage but will pull what ever i hook up to. I like that but i need better fuel milage mine is around 11 mpg to 12.6 at the best or is the new 2012 any better on fuel milage

I have a 2011 with 3.31 rear and 18s, I traded a 2009 with 3.73 rear and 20s. The 2011 will smoke the crap out of my 2009 even when I was deleted and running the Spartan 210 tune on the 6.4L. My towing mileage towing ~ 8K went from 11 with the 2009 to 14 with the 2011. At the time I towed, the 2011 had 1,500 miles on the ticker. I run 20+ on the highway around 70 mph and 16-18 mpg on my work commute and normal driving. I couldn't be happier.

 

[Vanilla Gorilla]

I agree with your tire choice. I'm running a set of 34.5" Nitto Trail Grapplers right now on my 2012 F250 that I ordered with 3.31's and 275/70R18 tires.

I have had no problems with power, or towing up to 8000 lbs. I have seen a loss of about 1 mpg with the bigger/wider tires due to higher rolling resistance I guess. Either way, the truck looks much better and is more useful off road with the bigger tires. I would never go back.

One question though, was your dealer able to re-program your speedo for the 20's? I started a thread on the subject yesterday. My dealer is having problems getting it done.

 

[summitman6.7]

I had my service manager reprogram for the 20's. The 1st thing we tried was just program the 20" wheels with 3.31 gears. When we fired the truck up, the check light can on. Checked codes, it said it didnt like our wheel/gear combo. So when we tried to tell it that we had 3.55 gears & 20's. So far so good. I was worried about speedo & trans shifting, but it hasn't been an issue. I have 3500 miles on the truck sence the reprogram & its good to go so far.

 

[Clhelget]

Tire size decision update

I agree with your tire choice. I'm running a set of 34.5" Nitto Trail Grapplers right now on my 2012 F250 that I ordered with 3.31's and 275/70R18 tires.

I have had no problems with power, or towing up to 8000 lbs. I have seen a loss of about 1 mpg with the bigger/wider tires due to higher rolling resistance I guess. Either way, the truck looks much better and is more useful off road with the bigger tires. I would never go back.

One question though, was your dealer able to re-program your speedo for the 20's? I started a thread on the subject yesterday. My dealer is having problems getting it done.

I was researching posts and have the same gears and want the same tires as stated above. It's now over a year later. Do you still agree with your decision?

 

[Vanilla Gorilla]

I have experienced no problems with either the combination, or my local dealers taking issue over the past year. I have checked back with the dealers several times and was told they have been unable to change the settings from the factory on other trucks as well, so it does appear that FORD has locked all of us out which of course is ridiculous.

If you plan on going the programmer route, several out there will allow you to correct the speedo. I'm still running stock programming and just living with the 2-3% error.

I do believe since that since programming is the ONLY viable option for correcting the speedometer error when changing to a bigger (but still factory available diameter), you have an arguable point if a dealer attempts to void your warranty for programming. That being said, it's not a fight I'm willing to take on. I love my truck as it is and could not be happier. Hope that helps- 'Gorilla

 

[cford716]

I also have Nitto 295/70/18's. My truck came with 3.31 axle and 275/70/18's. However, my speedometer read 3mph fast with the stock tires. Per my GPS it is now exact with no changes running the Nitto's.