37's and 3.21. Here I go again...

I didn't realize that the OP had a V6, that would probably sway my decision. That's almost a 140 hp difference.

I know that a 37 tire isn't the best option mechanically for the 3.21s but I guess my only argument would be is that everyone usually sticks to "go with 35s" but in reality most 35s are E rated and heavier than some D rated 37s. For example a 35x12.5r18 Nitto and Toyo Mt is 81lbs where my BFG 37s I had were only 74lbs and they ran small. I guess what I'm trying to say is 1.5" in diameter more detrimental than the additional weight of an E rated 35? I'm just a knuckle dragger and not that smart...lol

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Maligator said:

I guess what I'm trying to say is 1.5" in diameter more detrimental than the additional weight of an E rated 35?

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Weight is far more detrimental than diameter.

skyline090 said:

Putting 37"s on any truck running anything less than 4.xx gears isn't wisest decision. Do you want the look more than practicality and reliability? I ran 33s, on my '12 JK (3.21s) and even with the manual trans it was a dog. A full size pickup, with the same motor; more weight, more frustration.

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Is that graph supposed to show rpms with all the numbers? Because that’s not really accurate...at all. I would assume that’s rpms at a 1:1 transmission gear ratio at say 60 mph, that’s a guess. Can’t forget almost every vehichle has an overdrive (2 in fact, for most ram transmissions) and lockup which drops another few hundred rpms. My truck with 4.56 gears and a .67 final gear ratio sits at 2000 rpms at 60 mph.


Another thing to remember is the 8 speed transmission has a 4.5 or something first gear ratio. Your truck from way back in the day probably had a 4 speed with like a 2.5 first gear ratio. That makes a HUGE difference, when the new truck gets to 3rd gear to be equivalent to an older transmission 1st gear. The 8 speed has the best of both worlds, great acceleration due to transmission low gears, and low rpms at cruise because you’re using a longer rear end gear at cruising.


I Bleed Ram Trucks

chrisp2493 said:

Is that graph supposed to show rpms with all the numbers? Because that’s not really accurate...at all. I would assume that’s rpms at a 1:1 transmission gear ratio at say 60 mph, that’s a guess. Can’t forget almost every vehichle has an overdrive (2 in fact, for most ram transmissions) and lockup which drops another few hundred rpms. My truck with 4.56 gears and a .67 final gear ratio sits at 2000 rpms at 60 mph.


Another thing to remember is the 8 speed transmission has a 4.5 or something first gear ratio. Your truck from way back in the day probably had a 4 speed with like a 2.5 first gear ratio. That makes a HUGE difference, when the new truck gets to 3rd gear to be equivalent to an older transmission 1st gear. The 8 speed has the best of both worlds, great acceleration due to transmission low gears, and low rpms at cruise because you’re using a longer rear end gear at cruising.


I Bleed Ram Trucks

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I found that graph here on the forum so it may be for old 6spd autos. Nuisances in data aside, there is far more consistency in empirical data support running 37s on 3.21 gears is anything but optimal.

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skyline090 said:

I found that graph here on the forum so it may be for old 6spd autos. Nuisances in data aside, there is far more consistency in empirical data support running 37s on 3.21 gears is anything but optimal.

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Here is a similar chart. It’s not accurate at all. It’s listing a 1:1 ratio at 65 mph, with a manual transmissions. So the rpms are off by about 1000rpms. That chart shows 4.56’s with a 33” tires as 3018 rpms. My truck is at about 2150roms at that same speed. So not even close.

https://auto.howstuffworks.com/auto...wing/maneuvers/gear-ratio-tire-size-chart.htm

Old truck (545rfe) with 4.56 gears

First gear ratio 3.00:1 = 13.68 first gear ratio



New truck with 8 speed, 3.21 rear end

First gear 4.71 = 15.1 final ratio.

So you can see how much the newer transmissions change the effect ratio and why they accelerate better with a longer rear gear. Bump that up to a 3.92 stock gear and that will solve any problem a 37” tire has



I Bleed Ram Trucks

You better change your gearing. I had a 13 with 3.21 and the 8 speed, all stock. I cannot imagine putting 37s on it that way. If you tow with it, you’ll even have more issues. Heck, if I decide to put 37s on my power wagon with 4.10s; I’d probably have to re-gear too.


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turnerje said:

You better change your gearing. I had a 13 with 3.21 and the 8 speed, all stock. I cannot imagine putting 37s on it that way. If you tow with it, you’ll even have more issues. Heck, if I decide to put 37s on my power wagon with 4.10s; I’d probably have to re-gear too.


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These two guys are in it for the looks. They aren't towing..just showing. I give them 6mo before they want to re-gear.

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Interesting how the OP hasn’t said a word since he started the thread ...

It was a noticeable difference between my oem 265/70/17 (31.4”)and my current 305/55/20(33.2”) on my acceleration. I have 3.21’s. The weight difference in the tires is the culprit. That being said adding a PC, intake and exhaust negated much of that loss...but I have the 5.7. Its still pretty quick and powerful.
In response to the posts about “built to tow 4-10k lbs” I just think how hard that makes the powertrain work. Its not like you can unhitch the 37’s...Even with the 8spd on stock tires that V6 is working its ass off to move a big heavy mass. To get 300hp out of a NA 6 cyl is awesome, but it is asking a lot out of smaller motor. To lessen the load, regearing it seems to be the smart option for the longevity of the truck. Just my 2cents...

skyline090 said:

These two guys are in it for the looks. They aren't towing..just showing. I give them 6mo before they want to re-gear.

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Yes correct, I am not looking to spin my wheels, or drive like a speed demon on the highway, or to tow anything.

I got the truck because I like first of all how it looks period, adding a lift, wheels and tires only adds to the looks of my truck. If I wanted to tow I would of gone with a 2500 or 3500, or a Cummins, If I wanted to fly down the highway I would of gotten an SRT10 or other type of sports truck.

To me the Big Horn has the best of both worlds, you can tow if you "need" to, haul ass if you "need" to and play in the dirt if you "need" to as well.

Not everyone is looking for optimal performance and those that understand that by adding certain aftermarket parts can decrease their truck's performance do it knowing so.

I can sacrifice a bit of performance just to get the look I want on my truck, if later down the road I need to regear then so be it, but having 37s with a 7" lift is something I really want and I think I should be able to, I mean it is my money right?

I understand the risks, that is why you ask questions and it is up to Me or those who ask for advice if they will take it or not. Asking these questions is us educating ourselves about the things we might do or will do to our trucks.

So with that said, I thank you all for all the feedback, advice, recommendations every bit of knowledge that you guys have posted not only on this thread but all over these forums.

ThunderMug95 said:

It was a noticeable difference between my oem 265/70/17 (31.4”)and my current 305/55/20(33.2”) on my acceleration. I have 3.21’s. The weight difference in the tires is the culprit. That being said adding a PC, intake and exhaust negated much of that loss...but I have the 5.7. Its still pretty quick and powerful.
In response to the posts about “built to tow 4-10k lbs” I just think how hard that makes the powertrain work. Its not like you can unhitch the 37’s...Even with the 8spd on stock tires that V6 is working its ass off to move a big heavy mass. To get 300hp out of a NA 6 cyl is awesome, but it is asking a lot out of smaller motor. To lessen the load, regearing it seems to be the smart option for the longevity of the truck. Just my 2cents...

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I "will" eventually regear, but right now the money I am spending is for the lift, wheels and tires. I doubt that waiting a few months is going to destroy my truck ... my average speed in the city is 55, on the highway 70 lol ... I want to enjoy my driving and maybe just maybe once in a while I let the pedal hit the floor just for the hell of it ...

Wyatt Blakeley said:

Hey everyone. I've finally decided I want to do a six inch lift with 37's on my 2015 Ram 1500. I see posts that say it is an absolute dog and those few rare posts that say 3.21 with 37's don't seem to be an issue whatsoever. I feel like I am way too stuck on 37's and how nice they look. But I want to make sure I'm not going to tear things apart in a month. I have the 8 speed tranny (of course) which I've heard helps a little bit of the 6 speeds. I don't live in a hilly area but I do end up driving up and down some hills every once in a while. I would say my driving is 75% city and 25% highway. But when I say city I mean country roads that are 55 MPH and are usually a few mile strips. I get everyone says not to but the people who say not to never had any experience with the setup. I guess that's why i'm still stuck on 37's. I also don't get why it isn't just like a load from a trailer. I get there is more revolutions but I feel like it can't be that big of an issue... Any input is appreciated.

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have not seen a single 27 set up that looked decent. Don't know what it is about those or you who go for these, don't make sense !!!

boblonben said:

have not seen a single 27 set up that looked decent. Don't know what it is about those or you who go for these, don't make sense !!!

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I'm a mall crawler type of person 26" with 37s look good lol.

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if you don't change the gear ratio to near 4.0 the tranny will overheat and you'll fry the torque converter, possibly even causing a tranny oil leak, spray on the exhaust, and it'll catch fire. Been there done that.

Wyatt Blakeley said:

Hey everyone. I've finally decided I want to do a six inch lift with 37's on my 2015 Ram 1500. I see posts that say it is an absolute dog and those few rare posts that say 3.21 with 37's don't seem to be an issue whatsoever. I feel like I am way too stuck on 37's and how nice they look. But I want to make sure I'm not going to tear things apart in a month. I have the 8 speed tranny (of course) which I've heard helps a little bit of the 6 speeds. I don't live in a hilly area but I do end up driving up and down some hills every once in a while. I would say my driving is 75% city and 25% highway. But when I say city I mean country roads that are 55 MPH and are usually a few mile strips. I get everyone says not to but the people who say not to never had any experience with the setup. I guess that's why i'm still stuck on 37's. I also don't get why it isn't just like a load from a trailer. I get there is more revolutions but I feel like it can't be that big of an issue... Any input is appreciated.

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I have 3.21's on my truck and running 38 inch nitto ridge grapplers. I have the 6 inch suspension with 3 inch body lift. But also did the super chip upgrade with flowmaster exhaust and cold air intake. Even with 38's it jumps on acceleration. Never had issue and it's been 2 years so far. I had 37's on my truck with the 6 inch lift as far as look, I think you would be disappointed. That's why I did the 3 inch body lift and upgraded to 38s. But if you are going on looks alone go with the 6 inch lift and 35s. Get yourself some performance upgrades with it.

Here is mine with 37's. These are the nitto grappler G2's. From the pic it doesn't look like it has a 6 inch lift. It's a lot of tire and takes a way the rake you would want.

CAG CheechDogg said:

That is also what I keep asking people, if these trucks are meant and "CAN" tow/haul anywhere from 4,000 to 10,000 lbs ... someone please explain to me the difference from 37, 38 or 40" wheels and towing 4,000 to 10,000 lbs ... funny that Wyatt mentioned that because we were talking about this very topic at work during lunch ... just makes no sense ...

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Exactly. It just doesn't make any sense

Maligator said:

I didn't realize that the OP had a V6, that would probably sway my decision. That's almost a 140 hp difference.

I know that a 37 tire isn't the best option mechanically for the 3.21s but I guess my only argument would be is that everyone usually sticks to "go with 35s" but in reality most 35s are E rated and heavier than some D rated 37s. For example a 35x12.5r18 Nitto and Toyo Mt is 81lbs where my BFG 37s I had were only 74lbs and they ran small. I guess what I'm trying to say is 1.5" in diameter more detrimental than the additional weight of an E rated 35? I'm just a knuckle dragger and not that smart...lol

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Not sure where you got a 140 horsepower difference. My year on my truck makes 305HP. Current date Hemi's make 395. Not to say that all of it is even go to the wheel in either engines but its not a 140 difference.

Sorry I must've been looking at torque numbers

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Maligator said:

Sorry I must've been looking at torque numbers

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You’re good

Long ass thread that I skimmed through, looks like some good convo.

For some perspective, I'm running 37x13.5 on my 15' w/ 8 spd and 3.92. I can break the tires loose no problem, often by accident, but I also have full bolt ons without tearing into the engine and a custom tune.

I'm sure the 3.92s have a lot to do with breaking them loose.