Best HWY gear with 33" tires?

[Ram04]

I've read about 100 threads on 4:10 vs 4:56, 4:56 best all round gear period ect ect.

Couple things that don't quite add up to me;

Many say the sweet spot for mph with the 5.7 Hemi is 2000-2100rpm on hwy. I have found that 1700 is where my truck gets best hwy mpg (18-20 on a calm day)

This was with the smaller 245/17's and 3:55 gears.

I have since switched up to 275/20's and have just gone through a winter and wasn't as bad as expected, but definitely under geared. Specially driving around town.

After everything I've read, I am 90% convinced I should go with 4:10's, however, so many swear by 4:56 that I'm torn.

Add to that the place I called to do the job said the exact same thing; "Go with the 4:56, you will get better mpg even on hwy."

Now, I live in the prairies, so not much for hills ect. I could see if I lived around hilly terrain that 4:56 would be the way to go.

If I lived in the city and did 70+% of my driving there I could see 4:56 would be the gear to get.

But I live outside of town and probably do 70% hwy driving, although never over 70mph. Usually 60-65.

I do plan on doing some engine mods and I could see where a set of headers could change your sweet spot depending on what set you went with. (raise it in rpm if pipes are too large to retain bottom end tq)

The 04 Ram has always gotten very good mpg compared to most Ram owners I talk to, and I now contribute that to driving habits as well as the fact I had the smaller 245 tires which made the 3:55 gears a little better.

Still, while I can get great mpg on a calm day, any cross or head wind and the truck loses more mpg than any other vehicle I have driven.

This makes me think that maybe I could have done better with the same 245 tires and 3:92? (not as effected by strong winds/ elevation changes?)

Anyone out there running that combo and getting great mpg?

So when I originally did the calculation last fall, 3:88 was the gear that would put me right back to where I was with the 245's and 3:55 gears. So that would be the 3:92's.

I am turning larger heavier meats though, so that says 4:10 to me.

But everyone swears by the 4:56's!

Help!

 

[john p f]

My stock 275 60 20” tires are 33” tall and the 3.92:1 gear ratio is perfect for the 545rfe transmission on a quad cab.

 

[Ram04]

My stock 275 60 20” tires are 33” tall and the 3.92:1 gear ratio is perfect for the 545rfe transmission on a quad cab.

Do you drive a lot of hwy? Average speed and mpg? Do much towing?

Do you notice your mileage drop sharply with cross/ headwind or hilly terrain?

 

[john p f]

I’ve owned 2 with 392 gears. I live way out in open areas. Have hills and wind. Towed through the flint hills no problem with a Jeep TJ on back and 5 passengers. Just use towhaul. Cruise control worked great.

 

[Ram04]

Been researching this for a while now and I'm starting to come to the conclusion that many are finding the 4:56 to be a great gear for them because of the mods they have done that were anti productive for efficiency.

ie. go to 1 7/8" LT headers and 3" mid pipes and you are way out of efficiency range of mtr on low end.

Add 4:56 gears and all seems much better.

Wouldn't make sense for Chrysler to do all the research and then come out with a standard gear ratio that is not optimum for economy for any given application.

Having said that, I am still convinced that the 3:55 combo with 245/17's could have used a little more gear on days that are not calm, which is a large % of the time. Possibly a 3:77.

So starting to lean towards the 4:10's now.

 

[panoz3]

Just subscribed here. I have an 06, 4.7L with 3.55s and I have the exact same questions. It has 33" tires and it needs a regear to improve the mileage, but I also read about many Ram owners who switched to 4.56s. I'm with you though, I'm leaning toward 4.10s.

Sent from my XT1030 using Tapatalk

 

[Ram04]

After everything I've found so far I'm now 99% sure I will go with 4:10's.

Not easy to find answers on this stuff as so many make so many changes that things aren't apples to apples any more.

I was able to find enough feedback from people with mostly stock 5.7 3rd gens, 3:55 gears, that went with the bigger 33/20's and the ones who were paying attention all said the same thing;

Going to 4:56 gears they all lost about .5 - 1 mpg at 65-70mph hwy.

Now, don't get me wrong, if I drove 70/30 city/hwy I would be going 4:56 and never looking back, as they also all said the picked up 1.5- 2mpg city driving.

If I had the slightest inclination that I would eventually go bigger than the 33's I'd get the 4:56's.

If I already had 3:92's I wouldn't be changing anything, cuz just not worth it for the difference it would make.

Problem is I drive 70/30 the other way, hwy/ city, so the 4:10's are the way to go and I believe they will be slightly better than 3:92's in all but perfect conditions. (ie headwinds and cross winds as well as hilly terrain)

I also think that is why my guy who will be doing the gear swap suggested 4:56, because the 2 he did were both city dwellers who only went on the hwy occasionally.

That, or what many are doing to compensate for either poorly executed mods (put too large primary headers on/ exhaust and lost all bottom end) or for building a race truck where you are not concerned about low end tq/ drivability and you want the gear for going down the track.

 

[Ram04]

On the 3:55 gears with 275/20's combo. It's really not that bad to drive. Under geared yes, but with stock exhaust (mostly) she still has enough TQ down low that it's really isn't "doggy", just not as peppy as it was. So I can see how some can drive like this.

I've noticed though, that I tend to drive it more conservatively because you can just tell it's harder on the trans.

Coming through the winter, it seems I'm down about 1 1/2mph (US on the trip) average. So probably around 2mpg CND.

CND EPA in 04 sticker was (18l/100) 16mpg city/ (12.4l/100) 23mpg hwy. I've never seen that, but fairly close. Usually in the high 14l/100 range average in summer. (this # increases if I do too much city driving)

@ 65 on hwy cruise and calm day it would never hold 20mpg on the trip (US). Would start in the mid 20's, then slowly work down to average of 19.4 ish. @ 70 it would drop into the low 18's. Any head wind or cross wind and would drop a few more with ease. (which is why I'm thinking slightly under geared from factory)

EPA has changed, but pretty sure in 04 they were not using any real world #'s. Just dyno loading and maybe throw a guess for added resistance in there. The Ram is a bit of a porker, so wind resistance as well as over all weight is a big factor.

Slowly starting to warm up around here, so going to wait till it's 20deg again and do some hwy cruising in calm conditions with the 3:55's and 275/20's so I have an accurate comparison when the 4:10's go in.

Should be interesting, whether on even a calm day with perfect conditions and smooth level hwy cruising, the 3:55's with larger 275 can take advantage of the better gearing and increase in mpg, or if the weight and wind resistance of the Ram is just too much and can't match mpg because under geared even in perfect conditions.

 

[Ram04]

Weather has been nice and I got in a few test runs.

70-75deg days, one calm and one with even a slight tail wind.

The tailwind day really highlighted things;

Both at 60mph and 70mph with light tail wind the truck was down 1 - 1 1/2mpg from the 3:55's with 245/ 17's.

Add to that while driving today in traffic I believe I experienced the first time the clutch fan has engaged since putting the larger tires and rims on last fall.

Talk about under geared felling! Doggggggggg.

So after everything I've looked into I'm pretty confident in saying that these trucks were slightly under geared from factory. Possibly to give a better EPA #? (EPA didn't use wind resistance in their calculations back then)

So thinking the 4:10 with current tire size will be perfect for the driving I do. Looking to see MPG get right back to where they were before tire/ rim swap And, with proper LT headers and exhaust, pick up 1-2 more mpg and be getting the best mpg the truck has ever seen even with the larger tires!

I will up date later this summer when the 4:10's go in!

 

[panoz3]

Does your truck have 4WD? Are you installing the gears or taking it to a shop?

 

[Ram04]

Does your truck have 4WD? Are you installing the gears or taking it to a shop?

Yes, truck is 4WD.

While I am fully capable of installing the gears myself, I have a # of important projects on the go and will most likely have them installed by a local gear/ trans shop.

The headers and exhaust and everything else I will def do myself as it's not a big time consumer.