3.21 8speed and 37s

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Heucobob

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Just ordered 20x12-44 with 37x12.5
Anyone running this set up with the 8 speed and 3.21 gears . I have 2016 5.7 ram 1500
 

Markcuda

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With the extra weight the bigger tires will have and the high gears, you will regret the swap eventually.
The truck will be gutless.
 

69GWC

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Even if it still has enough punch for you down low your upper gears will be about worthless, its not going to want to stay in 8th gear at all imo unless your doing like 90mph.

If you do it I would plan on doing 3:92s sooner than later.

My 2 cents
 

Rzrman328

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Just ordered 20x12-44 with 37x12.5
Anyone running this set up with the 8 speed and 3.21 gears . I have 2016 5.7 ram 1500

Do some more research.

Lots of good info in this forum on this particular subject.
 

bryan28

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I had a 14 Sport with hemi 8spd and 3.21s and now a 17 with hemi 8spd and 3.92s. I'm running a 4" lift and 35s on my new truck. Didn't lift the 14 or put bigger than stock tires but I feel like the 3.21 and 35s combo would've been ok. Can't say how that set up would work with 37s but the 3.92 would be a better choice for sure.
 

6.7CumminsDrvr

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Around town won't be too bad but once you hit cruising speeds or highway you might have a bit of gear hunting and 8th might not be had until you are going REALLY fast.
 
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Heucobob

Heucobob

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Thanks for the info. I don't really do any highway driving . Its really used around town . I don't think really hit 8th yet lol would a tuner help ?
 

Witch

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Maybe take a look at 35's
 
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Heucobob

Heucobob

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The reason for my post was for people with first hand experience using this kind of set up . I appreciate all the feed back but most people that answer on this forum and other forums never really experienced this set up to give first hand experience .
 

MarshRam

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The reason for my post was for people with first hand experience using this kind of set up . I appreciate all the feed back but most people that answer on this forum and other forums never really experienced this set up to give first hand experience .

I don't have first hand experience on this, but am due for new tires soon so I had this discussion with a lift shop. He basically said everything everyone else is saying. I already have 35's on a 6" lift and holding mds is impossible, it's nothing other than a blinking light going in and out. I cannot hold a coast, not even going down hill. After installing CAI, tuner and exhaust, it helped a little, but not much. Based on my experience with the 35's and what everyone says, it is believable that it would be best to upgrade the 3.21's with 37's. I'll follow as I am still curious to hear if anyone is running this setup and their experience with it.
 
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Heucobob

Heucobob

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Thanks for the info . It's hard because I've been on other forums and hear so many different answers that's y I would like to hear it from someone that is really running this set up on a everyday in and around town
 

69GWC

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Kinda sounds like your going to be the guinea pig..lol

swapping the gears is not that bad, buy the rear gears and a lsd if you dont have one and they sell the front diff complete now at a fair price and just swsp it out.
 

Witch

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The reason for my post was for people with first hand experience using this kind of set up . I appreciate all the feed back but most people that answer on this forum and other forums never really experienced this set up to give first hand experience .


I run 37x12.5 with a 3.92 gear, and it took a huge hit

I added a lot modifications to get it where it needs to be
CAI, Exhaust, HF 93 oct. Tune, throttle body and a Pedal Commander

a 3.21 while I don't drive that will be decimated with 37's

like I said, maybe take a look at 35's
 

Rzrman328

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Thanks for the info . It's hard because I've been on other forums and hear so many different answers that's y I would like to hear it from someone that is really running this set up on a everyday in and around town

That why there's soo many different answers...it's everyone's opinion...nobody runs the setup you are wanting...because of all the reasons all these guys that have responded have stated.

I can only recall like 2, maybe 3 guys that have come on this forum asking questions about this type of setup...we never hear back from them. Either they ditch the idea or just don't come back on here to give their assessment.
 

MarshRam

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Thanks for the info . It's hard because I've been on other forums and hear so many different answers that's y I would like to hear it from someone that is really running this set up on a everyday in and around town

It seems if you are just running around town, have no need or desire of quick acceleration and don't care about gas mileage, you may be ok. However, what I would be most concerned with is long term strain on other parts of the vehicle. I'm with you on the 37's, I'd love to have them, but would it be worth it in the long run for a tire that is just slightly bigger is the big question. Other than the fact I commute 50 miles a day, this long term potential for other costly issues occuring is the main reason I am ditching the 37's. It's not worth the cash for me to regear to get them. Just going to assure when I get rid of my 1500 and upgrade to a 2500 Cummins, I'm going to buy the truck with the gears that will give me the option of bigger tires with some peace of mind.
 
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Heucobob

Heucobob

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Ok thanks . I got a email from a guy who said he runs this set up and shuts the mds off . He said he sees some Change in power but he expected that . For me personally I drive around town and put less than 5000 miles a year on my truck so I'm going to give it a go and I will definitely come back on and give u my honest opinion.
 

Trevor60

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excerpt pulled from the link

chart.html"]http://www.4x4offroads.com/gear-ratio-chart.html[/URL]

A simple formula for the correct gear ratio is this:

New Tire Size x Old Gear Ratio
New Gear Ratio = ―――――――――――――――――
Old Tire Size
Example:

The original tire size is 30" and the original gear ratio is 3.91. You plan on moving up to 38". Then the formula would be calculated as: (38*3.91)/30 giving you 4.95. Not all gear ratios are available so you have the choice between 4.88 and 5.13, 4.88 being the closest.

Choose a little bit lower gear ratios if you do a lot of off-road driving and a little bit higher if you do more long distance highway trips.


based on all my research people seem to like their final gearing to be 3.50ish when factoring in taller tires. this would suggest if you are going to do a gear swap u might want to look at 4.10 - 4.25 gears with 37" tires...YMMV

I need more power
Trevor
 
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69GWC

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Also has alot to do with the transmission as well, the 8sp is geared low in first gear compared to other ones so its not going to take as bad a hit as the 6sp truck would.
 

bchap05

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I'm going to put 35's on my 3.21 8 speed. But I'm also going to be picky about tire weight and wheel weight and shop for the most aggressive lowest weight set up.

Could possibly go 33's but planning on a 4 inch lift. So 33's probably make me look like I skipped leg day.

Also I've read quite a few people with 35's and 3.21 that said they barely noticed a difference. Seems most of those that say it sucks have 3.92's so they are just doing my gears are bigger kind of thing with no experience
 
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