3.21 gear ratio on 35s

[Nastyboypro]

Question... I purchased used lifted 2008 5.7 1500 with 35s on it. How can I find out what gears are in it?

 

[sdev11]

Those that have gear hunting, did you change the tire size in the system? I have 3.21 and 34” tires, once I changed the programmed tire size no more transmission hunting for the right gear.

 

[OldCarBum]

My 2017 Sport 4X4 has 3.21’s with the OEM 275/60/R20 tires.
I can cruise on the flat highway traveling 80mph @ 1500 rpm.
On my daily commute I travel through a canyon road that is a constant slight uphill grade with a 55mph speed limit. My transmission is constantly shifting up and down with the slightest change in the grade.
I’ve wanted to go to a 35” tire but can’t imagine what pulling any slight grade would be like.
I for one can’t figure out why all the truck manufacturers put 3.21’s in any light truck.
3.55’s or 3.92’s should be the minimum.

 

[Jebb]

Anybody running 35s with a 3.21 gear ratio?

Debating on if I should upgrade to a 3.92 or tough it out with 3.21s. Is there enough of a difference to make the swap?

I have 35s and 3.21 gears. It works good most of the time because the 8 speed has a very low 1st gear (lower ratio overall than the old 5 speed with 4.56 gears).

The problem, though, is on the freeway where 3.21/35 combo is too tall and bogs 8th gear a bit. When I start pulling the slightest grade or headwind the truck downshifts to 7 then back to 8 then 7 then 8....

SO - with 35s, ideally, you want 3.56 (for factory relationship) or 3.92 if you plan to pull anything.

But a gear swap is not so easy these days. I have a '17 1500 4x4. I can change the ring and pinion in the rear but the fronts are WELDED in. So for me to change to 3.56 or 3.92 requires replacing the entire front axle. So until I win the lottery I'm staying at 3.21.

BTW - to answer sdev11 - YES, I reprogrammed for the 35s with a tuner. It helped but does not fix the mechanical relationship that is still not per factory.

 

[Docwagon1776]

Question... I purchased used lifted 2008 5.7 1500 with 35s on it. How can I find out what gears are in it?

There are a couple of ways to do it, depending on if you have two people (easiest) and if you have an open rear diff or a locker.

If you have an open rear diff and two people:
Lift one rear tire off the ground and put a chalk stripe on it, or painter's tape, or whatever. You need a way to keep track of a rotation so you can stop it in the same position it started.

Chalk mark your drive shaft so it's easy to see when it has rotated a full turn.

One person rotates the tire by hand, the other watches the drive shaft.

Rotate the tire two full turns. How many times the drive shaft turns is then your ratio.

If you have a locker, you only turn the tire once but both tires need to be in the air.

*OR*
If you have a camera or a mirror-on-a-stick, you can leave both tires on the ground and just roll the truck forward one rotation of the tire while watching the driveshaft remotely.

If you don't have a way to watch or record the drive shaft while the tire rotates, stick some tape (or tape a thin rope/string) to the bottom of the drive shaft so that it hangs down like a streamer, then rotate the tire, then look how many times the tape wrapped around the drive shaft.

 

[JoeCo]

Question... I purchased used lifted 2008 5.7 1500 with 35s on it. How can I find out what gears are in it?

There are a couple of ways to do it, depending on if you have two people (easiest) and if you have an open rear diff or a locker.

If you have an open rear diff and two people:
Lift one rear tire off the ground and put a chalk stripe on it, or painter's tape, or whatever. You need a way to keep track of a rotation so you can stop it in the same position it started.

Chalk mark your drive shaft so it's easy to see when it has rotated a full turn.

One person rotates the tire by hand, the other watches the drive shaft.

Rotate the tire two full turns. How many times the drive shaft turns is then your ratio.

If you have a locker, you only turn the tire once but both tires need to be in the air.

*OR*
If you have a camera or a mirror-on-a-stick, you can leave both tires on the ground and just roll the truck forward one rotation of the tire while watching the driveshaft remotely.

If you don't have a way to watch or record the drive shaft while the tire rotates, stick some tape (or tape a thin rope/string) to the bottom of the drive shaft so that it hangs down like a streamer, then rotate the tire, then look how many times the tape wrapped around the drive shaft.

Since it's used and modified, hard to say if they've changed the gears or not, but if they are stock you could look up the build sheet as well. I've never looked up a 3rd gen but works for 4th gens and up and I was looking up TJ wranglers back to 1997 a month or two ago with it, so I'd assume it would work for 3rd gen rams as well. Link here if you want to check just for fun:

FCA RAM

fcacommunity.force.com

 

[Mbrigh3]

I swear my transmission issues on my 4th gen were related to 3.21 on 35's Ill never do it again. If I wanted 35s I would have gone 3.92.

I went gear hunting twice in the mountains. Both times it threw me into limp mode aka 4th gear.

Go 33's its what I did.

 

[TestPilot57]

Anybody running 35s with a 3.21 gear ratio?

Debating on if I should upgrade to a 3.92 or tough it out with 3.21s. Is there enough of a difference to make the swap?

Are you unsatisfied with the 3.21s?

I have always gone for the highest number/lowest ratio gears available in any truck I've owned. If I were a salesman, driving 50k a year, my goals would be different. But with a truck, that I drive 5-10k per year, gas mileage is less than insignificant. So I always go for the most available power.

If you already have 3.21s it's going to be a much tougher question. That's one reason I always spec and order my trucks. It's just a few dollars to make the change when buying new. After the fact - not so much.

 

[Nastyboypro]

There are a couple of ways to do it, depending on if you have two people (easiest) and if you have an open rear diff or a locker.

If you have an open rear diff and two people:
Lift one rear tire off the ground and put a chalk stripe on it, or painter's tape, or whatever. You need a way to keep track of a rotation so you can stop it in the same position it started.

Chalk mark your drive shaft so it's easy to see when it has rotated a full turn.

One person rotates the tire by hand, the other watches the drive shaft.

Rotate the tire two full turns. How many times the drive shaft turns is then your ratio.

If you have a locker, you only turn the tire once but both tires need to be in the air.

*OR*
If you have a camera or a mirror-on-a-stick, you can leave both tires on the ground and just roll the truck forward one rotation of the tire while watching the driveshaft remotely.

If you don't have a way to watch or record the drive shaft while the tire rotates, stick some tape (or tape a thin rope/string) to the bottom of the drive shaft so that it hangs down like a streamer, then rotate the tire, then look how many times the tape wrapped around the drive shaft.

Thank you... Army Strong

 

[Socalramfan]

Question... I purchased used lifted 2008 5.7 1500 with 35s on it. How can I find out what gears are in it?

You can also do a VIN search with Mopar and retrieve the build sheet. If anything it will tell you what your Ram came out of the factory with.

 

[TestPilot57]

what your Ram came out of the factory with.

For sure. BUT, it's certainly possible someone changed them out. If you are no the original owner the only way to know for sure is to (easy way) measure the revolutions, or, hard way - open the diff and count the teeth.

 

[Socalramfan]

For sure. BUT, it's certainly possible someone changed them out. If you are no the original owner the only way to know for sure is to (easy way) measure the revolutions, or, hard way - open the diff and count the teeth.

Most definitely. It'd also be true and most unlikely that someone would have 3.92's.... and change to 3.21's. Not impossible.... but not likely

 

[southbronxems]

I have 3.21 and 35s for on my 2013 for about 7 years now. My truck has almost 270,000 miles. I do a lot of highway driving, and occasionally tow a trailer thats about 6,000 lbs. Other than towing the trailer up a steep hill, there is almost no noticeable difference with 35's to me. I have a 3" leveling kit in the front and a 2.5" leveling kit in the back. They fit fine, and ride quality is like new except the tires are a bit stiffer as I run them at 40-45 lbs. I use stock 20" rim, and tire is an Interco Cobalt M/T size 35x12.5 r20. No issues...

 

[DILLIGAF]

Anyone who says there's no issues with 35s and 3.21 has obviously never driven a properly geared truck ...lol...

 

[TestPilot57]

Anyone who says there's no issues with 35s and 3.21 has obviously never driven a properly geared truck ...lol...

In the old days of a 4-speed, for sure. But I'd be pretty sure that a modern 8sp will be WAAAY better than a '70s 4 sp with 3.92s or even 4.11a

 

[Uncle Damo]

I'll speak from my experience.

My '14 Sport came with 8 speed, 3.21 ratio, factory 20's, and the tires were almost 34". After 30k miles I upgraded to 35's on aftermarket 20's. I am running a HemiFever PCM/TCM tune which changes the shift characteristics a bit.

My last truck was a 2500 Cummins with 4.10's so I know what "proper" gearing feels like. It was a stump puller but I was towing a heavy 5th wheel and it worked very well.

Today I have a 6k lb toyhauler that is loaded up to about 9k max; I've towed with this setup about 6k miles in Southern and Central CA deserts and mountains.

Unloaded, I have zero complaints. The truck pulls strong off line, cruises freeways at 20mpg, rides better than stock (upgraded suspension), and the tranny doesn't hunt at all on flats or in the hills.

When towing, sure I'd love the diesel again, but I'm certainly not suffering. The 8sp has a very low 1st and gets off the line fine, even on steep hill starts. Shifting is crisp and plenty of gear ratios to find the sweet spot. Minimal or zero hunting in the steep ups, it locks in to the right gear and generally stays there, and on the steep downs it does the same to control speed quite well.

So for me, it's a darn good setup that works well enough and balances economy, comfort, and capability. Haven't found a compelling reason the change it.

 

[Duece]

I have a little more interesting/specific question on this. I just upgraded to 35x12.5x20 tires with a 15' 5.7 with the 8 speed and 3.21's. I don't tow much, but when I do it is a Polaris Ranger (not usually a big deal, and (here's the kicker) an airboat (South Florida). The airboat is easily a couple thousand pounds, but the cage and motor behind it is like dragging a parachute down the highway. I just towed it today and it was a struggle to run 60 in 5th gear. My question is what ratio do I go to in order to get a little better performance but not kill my gas mileage when I'm just driving regular. I've seen 4.56 suggested but I had a late 80's Ford with 4.10s (or something near that) that would only get about 200 miles per tank (it had 2 tanks though). I had to swap that to 3.73's when I went to college, or else I was going to go broke! Anyhow, is 3.92 enough?! Is 4.56 too much? I tow the boat about a dozen times a year, so again, I don't need to have a rig that's a towing machine, just one that can run on these Florida highways without getting run over by faster traffic. I never haul a trailer over 70 mph anyways, but it would be nice not to be a struggle to get there and/or overwork the engine/transmission. TIA.

Edit: Also, how difficult is it to do a gear swap on this year truck? I believe I read somewhere some of these had welded front differentials?!

 

[69GWC]

My last truck had 3:21s 8sp and 35s and had zero problems out of it Except like what had been stated that it does not like staying in 8th gear on the hwy unless it’s flat ground or your doing 80mph.
Pulling my camper never gave me any issues even at over 7k .
Truck would still light the rear tires up easy. Sure 3:92s would be better no question but I never had a problem.

 

[RamElliot]

I drove my truck for almost a year with the 37s and 3.21s .... it wasn't until I drove from California to Arizona that I noticed the gear hunting going uphill .... I then drove another 1500 with 4.56s and 37s and another with 4.88s with 37s and that made me re-gear my truck right away ...

The MPGs I don't care about because this is a truck, what I do care about is the wear and tear on the trans and other things that would cost more than gas lol .... glad I re-geared mine

What gear did you choose?

 

[TotallyHucked]

I'd love to drive a 3.21 truck to see how it feels compared to mine and my dad's 3.92 trucks. I've only ever driven 3.92 or 3.55 equipped Rams with stock size tires or 305/55/20s which are shorter than stock. I'm really struggling with which tire size to go with. Since I have 3.92s I feel like I could run a 295/65/20 without hurting my mileage or power too terribly much. My commute is 80% 45-60mph roads with a short jaunt on the hwy.