3.21 gearing on 35's

dotnetrob · Apr 8, 2016

I know this question has been posted many times, have read many post on many forums, but I am hoping for some real world jeepers running 3.21 on 35's.

My 2015 JKU with automatic that currently has a 2.5" TF coil lift and is running stock wheels/tires. Next mods will be new control arms and trackbars, then wheels and tires or regear?

I have seen all the graphs/charts and understand most of the math with running 35's on 3.21, would probably switch to 4.56 of 4.88, but I am looking for real world users. Re-gearing has always been on my list, but its always been after 35's. And yes I would be using a recalibrator to adjust for tire size.

I drive ~70 miles a day on my jeep during the work week, mostly highway at 60-75 mph, I put a ton of miles on my jeep, 24k in the first year.

So to those real world jeepers on 3.21 with 35's and those who have actually run it...

How does it perform?

Does 5th gear exist?

What RPM's are you at when you hit 60-75mph on the highway?

Do you regret not re-gearing first?

Whats your mpg with 3.21 on 35's?

Other thoughts?

Thanks in advanced.

Jk909 · Apr 8, 2016

I ran 3.21 gears with 35's for about 6 months. I have the 3.6L with auto trans. 5th gear was basically useless. I think at 70mph I was at 2000 rpm's. If you want torque go with 4.88 if you want a little more mpg on the highway go 4.56

Journeyman · Apr 8, 2016

Save your cash and re-gear when you jump to 35's!
It's a jeep. Forget about fuel mileage!

austin160 · Apr 8, 2016

I wouldn't do it. I run 33's on 3.21 with a manual 2016 and it is sluggish, especially at highway speeds. Save up and regear. I average 17.5-19 mpg's right now driving 50-65 mph everywhere I go and rarely use 6th gear.

DGP · Apr 8, 2016

So I have a 3.8 auto that I commute with 35" tires and wheel with 37's. It had stock 4.10 gears that I ran with for six years. I just recently regeared to 5.13 and can't believe the difference. I could not imagine running 35" tires with 3.21 gears. I understand your motor is more powerful but I would recommend going with 4.88 as soon as you can. You will rot regret it. I wish I would have regeared mine years ago.

Goldeneagle1LC · Apr 8, 2016

I had a TJ with 3.21s and 35s. My best friend has the 3.8 with 3.21s and 33s both are 6 speeds. 5th gear is useless and 6th is just to lower the rpms on flat interstate. We both live in Florida so its not to bad but to even go up an over pass its a downshift to at least 4th sometimes 3rd for taller bridges. Thats why the JK I'm waiting on is going to have 4.10s. Regear at the same time as tires.

Clifford33 · Apr 8, 2016

I am currently running 35s with 3.21 gearing and I drive my jeep a lot not everyday I have my work car for that but For now it's not bad very sluggish up hills heck even when I had 33s it was sluggish. But not a huge difference really. If you drive a lot of hills like me I would re gear while you go to 35s for now I'm still stock but 4.88s will probably be going on my jeep soon. My jeep is also a 3.8 auto.

sipafz · Apr 8, 2016

Isn't your ride a dog already with your stock 32" tires?

dotnetrob · Apr 8, 2016

sipafz said:
Isn't your ride a dog already with your stock 32" tires?

Performance right now seems fine to me, getting ~19 mpg, even with my heavy foot (i like the sound of my exhaust) :blush: It doesn't perform like some sport car but its a jeep...

Samlautranger · Apr 8, 2016

I recently test drove a 2014 JKU with 35" tires and 3.73 gears, and it rode like a dog.

When I had a 2012 manual Rubicon with 4.1 gears, it rode much better than stock once I went up to 315 tires.

According to the chart I am looking at, for the 3.6L engine, seems with an Automatic transmission, 4.1 gears would be ideal for 315 or 35" tires.

3.73 gears for 33" tires.

swampdog · Apr 8, 2016

Samlautranger said:
I recently test drove a 2014 JKU with 35" tires and 3.73 gears, and it rode like a dog.

When I had a 2012 manual Rubicon with 4.1 gears, it rode much better than stock once I went up to 315 tires.

According to the chart I am looking at, for the 3.6L engine, seems with an Automatic transmission, 4.1 gears would be ideal for 315 or 35" tires.

3.73 gears for 33" tires.

I don't know how to prove this, but that chart is wrong. 4.88 with 35s (metric or standard, whatever) is the right setup for a manual.

rogerk93 · Apr 8, 2016

I have 37's with 3.21 and I simply hate it. I'm saving to regear the rear end and my one tons for the front.

CarolinaJK · Apr 8, 2016

My 3.6 Auto on 35's and 3.73s is pretty damn sluggish. 3.21 would be really pushing it for me.

WJCO · Apr 8, 2016

swampdog said:
I don't know how to prove this, but that chart is wrong. 4.88 with 35s (metric or standard, whatever) is the right setup for a manual.

I think the experience of multiple people on a forum that run a certain setup is a much better resource than a stupid chart, lol. Especially when certain variables are included such actual vehicle weight, actual terrain, etc.

Samlautranger · Apr 8, 2016

swampdog said:
I don't know how to prove this, but that chart is wrong. 4.88 with 35s (metric or standard, whatever) is the right setup for a manual.

I guess the only way to really tell then would be to what? Run a manual with 35" tires with 4.1 gears, then 4.56 gears, then 4.88 gears and compare? Many other things as the other poster would come into play as well, 2 door vs 4 door (weight of vehicle), M/T vs AT tires, etc.

Be good if there was a more comprehensive analytical chart, showing all the variables. Instead one person says this is ideal cause it works for them, and another says another set up works for them. How accurate is the chart that is standardly used? :thinking: But, if not correct, would like to see another chart with the data.

But I think we can all agree on is that 3.21 gears is not ideal at all for 35, and God forbid 37, inch tires.

Dana · Apr 8, 2016

swampdog said:
I don't know how to prove this, but that chart is wrong. 4.88 with 35s (metric or standard, whatever) is the right setup for a manual.

Would you recommend 4.56 or 4.88 for automatics?

WJCO · Apr 8, 2016

Samlautranger said:
I guess the only way to really tell then would be to what? Run a manual with 35" tires with 4.1 gears, then 4.56 gears, then 4.88 gears and compare? Many other things as the other poster would come into play as well, 2 door vs 4 door (weight of vehicle), M/T vs AT tires, etc.

Be good if there was a more comprehensive analytical chart, showing all the variables. Instead one person says this is ideal cause it works for them, and another says another set up works for them. How accurate is the chart that is standardly used? :thinking: But, if not correct, would like to see another chart with the data.

But I think we can all agree on is that 3.21 gears is not ideal at all for 35, and God forbid 37, inch tires.

And what I was saying earlier for anyone reading this, is to read and research what people with certain gear combinations have already posted on the forum. So you can see what actually works and doesn't work based on those rigs and variables.

DMF · Apr 8, 2016

Having 4:88 gears and how I use my jeep is a little high for my liking. I have pretty good power but once I'm on the hwy I really feel bad for the motor. I don't think running 3k rpm is good for the longevity of the motor so I'm always around 60-65 mph to keep it under 3k rpm on the hwy.

rogerk93 · Apr 8, 2016

A little side not I don't think the chart is that accurate. At 70mph I'm at 2,050rpm that's with 3.21 and 37's the charts says I should be at 1694rpm. The way to find a solid answer is by following what people say who actually have ran the gear ratio with tire size

Brute · Apr 8, 2016

I ran 35's with 4.10 for 2 years...ok, but wished I had 4.56...when I went up to 37's, I regeared to 4.88 and it runs GREAT. I'm running a 5.7 hemi with a stock 5sp auto (W5A580)...

Check out this site for regearing calculator from Novak...they know their transmission stuff.

http://www.novak-adapt.com/knowledge/gearing/

Side note...with 37's in 5th gear (.83), I'm at 2800 rpm at 75 mph...

3.21 gearing on 35's

Regear or wheels/tires first

Regear first

Go ahead and get wheels/tires

Save and do both at the same time.

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