Gearing for 35's
JK Freak
Joined: Oct 2008
Posts: 974
Likes: 0
From: Canisteo, NY
Well if you have an auto and it's kicking out of overdrive your wasting more gas than running a little bit higher RPM in overdrive.
Same thing with stick, if you have to shift down and get your speed back up then your running higher RPM's in that lower gear. Not that great for gas mileage.
Ah crap, who cares about gas mileage?
JK Newbie
Joined: Nov 2008
Posts: 41
Likes: 0
From: the peg, canada
well
If the tranny is shifting in and out of OD on the highway your building heat in the tranny and its tough on it.
Reving the motor a little higher takes the load off the tranny. Also, if the motor is working harder at lower rpm, it will get worse mileage then reving higher.
The opinion is with the additional weight and tire size, the 3.8 auto is happy at 2400-2700 and you will likely get the best fuel mileage in this area. I believe I read maximum torque is up at 4000 rpm on these motors and that is why the higher rpm works nice unlike a V8 that has more torque and can pull 35s down the highway nicely at say 2000 rpm.
Reving the motor a little higher takes the load off the tranny. Also, if the motor is working harder at lower rpm, it will get worse mileage then reving higher.
The opinion is with the additional weight and tire size, the 3.8 auto is happy at 2400-2700 and you will likely get the best fuel mileage in this area. I believe I read maximum torque is up at 4000 rpm on these motors and that is why the higher rpm works nice unlike a V8 that has more torque and can pull 35s down the highway nicely at say 2000 rpm.
JK Freak
Joined: Mar 2008
Posts: 783
Likes: 3
From: Southeast
On 35s with a 6-speed I'm plenty happy with the Rubicon's stock 4.10 gears.
The 6 forward gears give you a lot of options with the torque of the little 3.8.
My previuos Jeep experience was with a 3-speed manual. Some of our younger enthusiasts find it hard to believe that any vehicle actually had a 3 speed manual transmission. Then I tell them about the old powerglide 2-speed auto!
Sure, with 4.88s you'd downshift less often comparedf to a stock 6-speed Rubicon, but 5th with 4.10s is just like 6th with 4.88s. And the Jeep pulls so cleanly down low now, that you can lug 6th pretty slow and 5th really slow, then pull away smoothly and cleanly.
And on the highway, 4th, 5th, and 6th are all very useable. Since the motor has broken in and spins happily up to over 5k, I don't hesitate to drop it in 4th where I need max power, and up and down on some of the hilly routes around here I just leave it in 5th, especially if I'm busy with the CB or radio.
And with 4 low gears acceleration is not a problem in town, I get up to 40-50mph pretty quick/easy and just drop it into 5th (or 6th) and cruise.
The auto with 5.13s is only spinning what, about 60-70rpm faster than the 6-speed with 4.10s when the converter is locked. And only OD and 3rd are actually useable at highway speeds. It really needs to be a 5-speed slush box.
I know the torque converter helps, but I actually hear very few brag on it's contribution.
The 6 forward gears give you a lot of options with the torque of the little 3.8.
My previuos Jeep experience was with a 3-speed manual. Some of our younger enthusiasts find it hard to believe that any vehicle actually had a 3 speed manual transmission. Then I tell them about the old powerglide 2-speed auto!
Sure, with 4.88s you'd downshift less often comparedf to a stock 6-speed Rubicon, but 5th with 4.10s is just like 6th with 4.88s. And the Jeep pulls so cleanly down low now, that you can lug 6th pretty slow and 5th really slow, then pull away smoothly and cleanly.
And on the highway, 4th, 5th, and 6th are all very useable. Since the motor has broken in and spins happily up to over 5k, I don't hesitate to drop it in 4th where I need max power, and up and down on some of the hilly routes around here I just leave it in 5th, especially if I'm busy with the CB or radio.
And with 4 low gears acceleration is not a problem in town, I get up to 40-50mph pretty quick/easy and just drop it into 5th (or 6th) and cruise.
The auto with 5.13s is only spinning what, about 60-70rpm faster than the 6-speed with 4.10s when the converter is locked. And only OD and 3rd are actually useable at highway speeds. It really needs to be a 5-speed slush box.
I know the torque converter helps, but I actually hear very few brag on it's contribution.
But, thats just my opinion, and just like but holes, everyones got one.
JK Newbie
Joined: Mar 2008
Posts: 79
Likes: 0
From: Las Vegas Nv
JK Enthusiast
Joined: Feb 2007
Posts: 249
Likes: 0
From: Bay Area
I agree -
I'm running 4.88s in a 6-speed with 35s. It's great off and on road. Mileage is around 14mpg, 80mph in 6th at 3000rpm. Pulls my trailer (too heavy) with no problem - over mountains in 4th.
I was looking at 5.13s, but was too impatient to wait a few months for them. Now, I'm happy I went with the 4.88s.
I'm running 4.88s in a 6-speed with 35s. It's great off and on road. Mileage is around 14mpg, 80mph in 6th at 3000rpm. Pulls my trailer (too heavy) with no problem - over mountains in 4th.
I was looking at 5.13s, but was too impatient to wait a few months for them. Now, I'm happy I went with the 4.88s.