3.21 gearing on 35's

[DoubleTrouble]

Gear chart is a guide. It shows you what gear you need to get your rpm's/power back. Then you have to consider added weight, geographic location, and terrain you plan on encountering. You just have to fill in the blanks. Where I live is flat for the most part. I have a 2012 jku auto with 35's and 3.73. 5th gear is just ok for me. Any time I have 4 adults or pull a small trailer it's less than desirable.

 

[Brute]

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...

If you run 35's with 4.88 gears and the 5sp auto, you will be close to 3000 rpm at 75 mph...if you run 4.56 gears, you'll be closer to 2700 rpm...

 

[sipafz]

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...

I recently drove a Sport "S" with the 3.21's and stock 32" tires up a Wisconsin hill (small) and knew quickly that I could not live with the lack of performance. I can't imagine making it worse with bigger tires. I suggest that you have a plan "b" ready after you get your tires.

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.

Nailed it!

 

[aldaman]

Like what others suggested, you should regear. As for the gearing chart, if I remember correctly it is based on actual tire measurement and not what's advertised on the sidewall, so if you have advertised 315s or 35s you should look at the chart gearing for 33-34" tires...

 

[OverlanderJK]

35's need 5.13's if you want power.

 

[SnailTrail]

I have a 3.6 auto with 35s and 3.21s. At first I didnt think there was a big difference but when I added my slabs it made it unbearable. At 70mph its fine but it does downshift fairly easy. And I only get 14.5mpg

 

[Murfphy]

I have a 08 sahara manual jk on 35's 4.88 gearing. Feels great of the line and moves. It does ok on the freeway. I hit some 4 and 5 story sand dunes last month with 5 people in her, hard top on, gobi rack, arb delux front bumper and didn't make it. 3 stories I made it but that 4th killed it. If I had 5.13 I think I would have been in there.

But she eats mad gas now. Next up is ls motor (or a r1m for speed) or a black ops ripp supercharger.

My 2cents.

 

[Ginlow]

I'm running 40X13.50 tires with 5:38 gears and a super charger, it's still lacking on the highway.

 

[Murfphy]

I'm running 40X13.50 tires with 5:38 gears and a super charger, it's still lacking on the highway.

Really!!? Wow.... is your rig super heavy also? Why do you think it's sucks at freeway speeds? ( trying to learn a bit here)

 

[WJCO]

I'm running 40X13.50 tires with 5:38 gears and a super charger, it's still lacking on the highway.

Not sure you can do much more other than an 8 swap. Eddie may have an answer for you when he gets back.

 

[Ginlow]

Really!!? Wow.... is your rig super heavy also? Why do you think it's sucks at freeway speeds? ( trying to learn a bit here)

I have a 2008 Jeep 4 door with the 3.8L v6, RIPP 2 supercharger and 42 RLE tranny. It does have a chevy 14 bolt rear and Dana 60 kingpin up front, but weight wise it's not too much more. going up hills I can get it to 60-65 with OD off, it will 70-75 downhill or on the flats with no head wind,while getting about 13 MPG, but like I said before it's seriously lacking in the power department. I guess it's a jeep and not meant for speed in the first place.

 

[Murfphy]

I have a 2008 Jeep 4 door with the 3.8L v6, RIPP 2 supercharger and 42 RLE tranny. It does have a chevy 14 bolt rear and Dana 60 kingpin up front, but weight wise it's not too much more. going up hills I can get it to 60-65 with OD off, it will 70-75 downhill or on the flats with no head wind,while getting about 13 MPG, but like I said before it's seriously lacking in the power department. I guess it's a jeep and not meant for speed in the first place.

So supercharger not worth the time and cost?

 

[Ginlow]

So supercharger not worth the time and cost?

I would not say that, I have read articles claiming the supercharger is very close in HP and TQ compared to the Hemi swap at a fraction of the cost, that being said I haven't driven a Hemi jeep so I can't confirm or deny the claims.

My supercharger is tuned to 400 Ft/Lbs of torque ATM and, I need to play around with the tuner a bit to see if it can perform better on the highway than it does now.

 

[IndyJeep]

I recently went to 35's with 3.21 and drive 56 miles each day for work... it was constantly searching for the gear it wanted and the gas mileage dropped to 15 or so on the interstate.... Enter Superchips flashcal to adjust speedometer and other fun stuff, and it was a major change! I have avg 19.5 for 2 days now, and shifts much more appropriately (similar to stock). It does lack low end power/take off, but it's a Jeep, not a sports car. I plan for 4.56, but Superchips definitely made a difference in the mean time.

 

[ST3LLA]

I have a 2014 JKU sport with 3.21 and 35s and get 15 mpg. I drive 30 minutes to school one way every day but it doesn't bother me except on hills. My dad has a '15 rubicon with 4.10s and stock wheels and tires and I would kill for his gearing.