The Big Picture........Fuel economy, tire sizing Tuning and Gearing

[Socalramfan]

After reading all the responses from another thread regarding OP's question on fuel economy has got me thinking as well.

Personally I'm not too worried about the mpg, but taking a look at the "effecientcy" of all parts put together has got me thinking more about a "Tune" and "gearing", as you do really have to look at the "Big Picture".

There are some other older threads on some of this, but wanted to give others from the initial thread a place to respond without Highjacking OP's thread

 

[kurek]

If you're talking about taking a holistic approach to it; fully agreed that's the essence of all good engineering. It also is the diametric opposite of what looks exciting on instagram or the cover of a magazine so nobody's going to do it.

In Japan some artists and craftsmen use the term shibui which refers to a visual aesthetic but also to an engineering economy of form that minimizes failure and consequence because everything is the correct size and shape for the actual task it must perform.

In Sweden some people appreciate the word lagom - the right amount is the best amount. Enough is plenty.

In America... well we don't have those words yet but we got more trucks than Japan and Sweden put together so I guess it'll be a while

 

[Socalramfan]

Hai Hai.... shibui (cool) So desune

Yes, there is always a "give and take" aka tradeoff so to say.

Granted most of the Rams here have bee taken vey well care of, and for the most part everyone has gotten their exteriors dialed in, or at least a vision of what they are shooting for.

I'll use me an an example..... visually I've got it set up with a MacTrax 4.5/3, 20" Fuel Mavericks, on Yokahama 35x12.5"x20 and a Vararam. For me and my purposes, that's the stance I was shoot for and achieved.

As a tradeoff, performance will decrease. How to address this? Proper tuning and gearing etc, which is what prompted the thread.

Others had mentioned they changed the above for their Rams which has inspired me to dig deeper, and get more specifics, and jump in on it as well. Just "ok" isn't good enough

The goal..... a good looking Ram that has been "optimized" to the best it can be ...given the mods I've chosen.

 

[WY-Dave]

The biggest think I found about about upsizing tires (from my Jeep days) is that re-gearing is highly recommended. When you go up in size without re-gearing you are dropping the RPMs and changing the effective ratio.
Even with going just from 33s to 35s. With the stock 33s and 3.73, the Jeep would always drop a gear on the slightest hill. When I went to 35s it was even worse. And a product of that was crappy mileage. On my trip to work every day I have about 5 miles of rolling hills then about 15 level. Playing with the stretch of the different types of roads. On the level I was getting 22+, on the hills it would drop down to 15s for an average of around high 16 to low 17s. And it was a slug for acceleration. I ran it like that for a week. When I re-geared to 4.56s, it was like night and day. The rpms bumped up about 300 rpms from stock @ 65. BUT, it stayed in OD on the same rolling hills that it would drop a gear. My mileage was a constant 18-19 mpg. I always heard the "didn't buy a Jeep for the gas mileage" bit, but the +4mpg change, made it 90 more miles per (22.5g) tank. At the 58k miles on trade in (and if I had done it first thing) 58k would take 3867 gals of gas. And at 18.5 it would take 3135gals. And right now with $3.42 gas, that is $2503 and for the 3 years I had it $834.48 a year. I could replace the tires every 2 yrs with that. Just for the curious, nothing else was down to the engine (CAI or other), and about 1000# of accessories was added between lift/tires/rims/bumpers/winch.

 

[Socalramfan]

The biggest think I found about about upsizing tires (from my Jeep days) is that re-gearing is highly recommended. When you go up in size without re-gearing you are dropping the RPMs and changing the effective ratio.
Even with going just from 33s to 35s. With the stock 33s and 3.73, the Jeep would always drop a gear on the slightest hill. When I went to 35s it was even worse. And a ide product of that was crappy mileage. On my trip to work every day I have about 5 miles of rolling hills then about 15 level. Playing with the stretch of the different types of roads. On the level I was getting 22+, on the hills it would drop down to 15s for an average of around high 16 to low 17s. And it was a slug for acceleration. I ran it like that for a week. When I re-geared to 4.56s, it was like night and day. The rpms bumped up about 300 rpms from stock @ 65. BUT, it stayed in OD on the same rolling hills that it would drop a gear. My mileage was a constant 18-19 mpg. I always heard the "didn't buy a Jeep for the gas mileage" bit, but the +4mpg change, made it 90 more miles per (22.5g) tank. At the 58k miles on trade in (and if I had done it first thing) 58k would take 3867 gals of gas. And at 18.5 it would take 3135gals. And right now with $3.42 gas, that is $2503 and for the 3 years I had it $834.48 a year. I could replace the tires every 2 yrs with that. Just for the curious, nothing else was down to the engine (CAI or other), and about 1000# of accessories was added between lift/tires/rims/bumpers/winch.

Totally agree.

Curious to hear what gearing others have matched up with 35's and 37's. I'm running 3.92 due to the tow package I've got.

 

[RLJ10X]

Social, you don’t say what transmission you have, but…

In my opinion, with the 545REF, 3.92s were too tall even with stock tires. 4.10s for stock tires. Probably 4.56s for 35s. 4.88 for 37s.

I’m not a fan of 3.21s even in the 8 speed. The Pentistar needs more gear than 3.55s, for sure!

When you gear down, you lighten the load on your transmission. The 545 could use all the help it can get.

There’s an old saying “Give me a lever and I’ll move the world “ . That should be changed to “Give me gears and I’ll move the world”.

 

[Socalramfan]

Great feedback (RLJ10X) thanks, and yes I overlooked the trans info.

It is a 545REF, and the engine is a 4.7, rear gearing 3.92 tow package.

Gearing is as well a tradeoff too. Tall gears, better high speed...... lower, quicker performance. Ideally I'd like to achieve the acceleration, without the engine screaming doing 75 down the freeway.

 

[CheechDogg.0n37s]

Well most already know that I have the 7" lift with 37x12.5R20 Ridge Grapplers on some 20x12 -44 offset wheels ... yes wheels make a difference too because some are very light and some are super heavy, mine are on the heavy side

I was on the same boat as you @Socalramfan when I first lifted my truck, then for a while I was like, "nope, don't need to regear at all, the truck runs just fine" which it actually did, my MPGs with the 3.21s was almost similiar to what I am getting now actually ..

Then I started seeing everyone posting about re-gearing and people around town asking me what gears I had ...... I finally said screw it and saved up the money to regear and SOB am I glad I did!

Before I got my Carven Competitor Series exhaust and only had the 4.88s, I was getting up to 17 mpg around town .... After I got the Carven lol, I dropped almost to 11 MPGs but because I loved to floor it just to hear the damn exhaust roaring as I careen down the streets ...

Then I started to chill out a bit and got back to a respectable 13-15 MPG around town, stop and go traffic and up to 17-18 MPG on the highway at 65-70 MPH ...

I don't drive fast anyways so my MPGs have always been better than most people, but with 37's you definitely should consider regearing to 4.88s .... with 35s 4.56s would be best ...

My buddy @the_goodguy07 also has a 7" lift with 35s and hasn't regeared, but did add AFE shorty headers and a pedal commander and he loves his truck ... he is going to eventually re-gear but right now there really isn't a need to do so ...

So my opinion is yes regear for 37s, 35s you can probably get away with not doing so but SOB is the truck gonnah feel so damn strong if you do lol ...and honestly FAWK MPGs lol, I didn't buy a truck to get good MPGs from the start ....

 

[Socalramfan]

Thank you sir, lots of good stuff.

Have you noticed any decrease in top end? Not that were driving 100+ (that would be illegal) , but you know how freeway driving is out here.

 

[RamminMopar]

I feel my truck pulls harder all around specially the top end with 4.56 because its already running more rpm and its closer to the gear next gear

 

[CheechDogg.0n37s]

Thank you sir, lots of good stuff.

Have you noticed any decrease in top end? Not that were driving 100+ (that would be illegal) , but you know how freeway driving is out here.

Top end dropped for sure but I rarely drive above 75 even on the freeway ... I have on occasion reached 85 without knowing and only notice because I am all of the sudden passing up other cars lol ...

 

[Socalramfan]

Top end dropped for sure but I rarely drive above 75 even on the freeway ... I have on occasion reached 85 without knowing and only notice because I am all of the sudden passing up other cars lol ...

I Hear ya

Have to see you Ram one of these days out here

 

[MOPAR78]

My MPG went down about 3 MPG when I put on the 37's, average now is 15 MPG. RC SWB with 8 speed & 3.21 gears. I did notice some hold back with the larger & heavier tires at first. I was considering stepping up to the 3.92 gears, but with the complete Stainless Works exhaust system installed, It's actually quicker than it was with the stock 33"s. So I'm not sure which way I'll go with the gear set up.

 

[Elkman]

The heavier the tire the more fuel will be consumed to keep it spinning and there is no getting around that. The grippier the tread the more fuel will be lost and that is why tractor trailer rigs run tires that nearly devoid of a tread pattern.

The best tractor trailer drivers average 15-20 percent more miles per gallon than the average drivers with the same rigs. Fleet operators know this and this is why they are keen on the newer automatic transmissions and navigation systems that adjust for the terrain, load, traffic, and other factors. A really good driver can do better than the automated system but there are not that many such drivers around.

I can guarantee that your fuel economy will improve if you improve how you drive. Avoid short trips, slow down before a stop, drive at the speed limit or slower (unless you are black in which case this can be very dangerous).