4.56 too much for 3.8 and manual?

72c10

JK Enthusiast
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Utah
Hi all! I've searched on here and Googled what I'm looking for. Maybe no one has shared. Found a guy with my same question 10 yrs ago on a JK forum and he never posted his results.

My Jeep: '07, 6speed manual, 3.8 w/ 285/70r17's (just under 33").

I just put a deposit down and waiting in line w/ a well recommended and reputable off-road shop. Went in to get 4.10s, threw the deposit down and got in line for a Yukon 4.56 install in a few weeks.

I see a lot of people very satisfied with the 4.56/6speed man./35" combo. However, has anyone ran or has a 3.8, 33", 6 speed combo and remember (or can tell me) if the revs were too high on the freeway/long trips? Say... 80mph (speed limit on I-15 here in Utah).

I trust everyone, including the shop owner - when I hear that I'll be happy w/ 4.56's - but, is that gonna be too much rev on long trips (3-5 hr trips) at 80mph?

Too much for me is 3000 and up. I swear he said I'll be 2700 in 6th at 80, but the chart I see online says 70mph and approx. 2700. Is that in 5th gear maybe?

Although, we do intend to rent a tent trailer a time or two in the future next year. I know I'll be very happy then!

These 33"s will last me YEARS, with as little as I drive my JKU and I'd go 295/70r17 max (shit, I'll prob end up with 35"s, huh?) later on if I go bigger.

Thanks in advance for any input!
 
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According to this, the 4.56 with a manual trans & 33" tires puts you right in the zone. Even if you moved up to a 35, you'd still be good to go.
If you're running down the road at 80 with a 4.56 in 6th gear with the 33's, you're probably getting close to 3k RPMs. 35's will put you in the perfect place to run 80.
 
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View attachment 120033

According to this, the 4.56 with a manual trans & 33" tires puts you right in the zone. Even if you moved up to a 35, you'd still be good to go.
If you're running down the road at 80 with a 4.56 in 6th gear with the 33's, you're probably getting close to 3k RPMs. 35's will put you in the perfect place to run 80.

I don't know about the manual chart, but the chart for the auto is right on the money.
 
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View attachment 120033

According to this, the 4.56 with a manual trans & 33" tires puts you right in the zone. Even if you moved up to a 35, you'd still be good to go.
If you're running down the road at 80 with a 4.56 in 6th gear with the 33's, you're probably getting close to 3k RPMs. 35's will put you in the perfect place to run 80.
Thank you, sir! I guess I could go the 34/35" route later on if I'm revving too much at 80mph on those trips. I don't ever want my Jeep to lug again, so I'll stay with the 4.56. I know I'll be glad I did when I tow a tent trailer to the mountains.
 
Hi all! I've searched on here and Googled what I'm looking for. Maybe no one has shared. Found a guy with my same question 10 yrs ago on a JK forum and he never posted his results.

My Jeep: '07, 6speed manual, 3.8 w/ 285/70r17's (just under 33").

I just put a deposit down and waiting in line w/ a well recommended and reputable off-road shop. Went in to get 4.10s, threw the deposit down and got in line for a Yukon 4.56 install in a few weeks.

I see a lot of people very satisfied with the 4.56/6speed man./35" combo. However, has anyone ran or has a 3.8, 33", 6 speed combo and remember (or can tell me) if the revs were too high on the freeway/long trips? Say... 80mph (speed limit on I-15 here in Utah).

I trust everyone, including the shop owner - when I hear that I'll be happy w/ 4.56's - but, is that gonna be too much rev on long trips (3-5 hr trips) at 80mph?

Too much for me is 3000 and up. I swear he said I'll be 2700 in 6th at 80, but the chart I see online says 70mph and approx. 2700. Is that in 5th gear maybe?

Although, we do intend to rent a tent trailer a time or two in the future next year. I know I'll be very happy then!

These 33"s will last me YEARS, with as little as I drive my JKU and I'd go 295/70r17 max (shit, I'll prob end up with 35"s, huh?) later on if I go bigger.

Thanks in advance for any input!
 
OK... just picked up the JK from the shop with the new 4.56 gears. I'm still easy on the throttle for the break-in...but damn - with the Pedal Commander on, it's a noticeable difference from 3.21 to 4.56. I'm a little hesitant to get on the throttle, due to break-in for the gears, so I'll update and see what RPMs I'm in at 80mph w/ 285/70r17 (33s) for future reference. Without the Pedal Commander on, the difference was not as noticeable, only that I would reach 3000 rpm a little sooner, but the acceleration didn't seem as if it was that much quicker. I turned it on halfway to my office and I REALLY saw a difference. I'll do a few heat up and cool down cycles and take it on the freeway in a day or two and update.
 
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Final answer:

4.56 gears, 6 speed manual, Falken AT3 285/70r17 (just under 33") tires on my 3.8 is....... 3300 RPM at 80mph.

SH!T! I'm gonna get rocks thrown at me, but I should've just got 4.10 gears. I wanted keep these 33"s and to be near 2500-2700 RPM at 80mph.

Im gonna hate running 3300 RPM on road trips. It shouldn't be bad for the motor to run 2-4 hrs straight at that RPM, should it? I just felt a good combo of mpg and less stress on the engine around 2500 rpm on long trips.

I was hoping these new tires would be on this Jeep for a few years, but I'll prob try to get some 285/75r17 or 290/70r17 to go 34" sooner than later, so I can drop those RPMs on long trips by a few hundred.

ON A POSITIVE NOTE:. I'm LOVING THE TORQUE in gears 3 thru 6 now tho. 1st and 2nd are a bit short, so take offs from a stop light are slower, due to having to shift a couple times so soon. But, it's a JEEP 😀 The shop told me not to off-road until I have my break-in and fluid swap done, but I'm sure I'll love it more on the fun terrain.
 
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Final answer:

4.56 gears, 6 speed manual, Falken AT3 285/70r17 (just under 33") tires on my 3.8 is....... 3300 RPM at 80mph.

SH!T! I'm gonna get rocks thrown at me, but I should've just got 4.10 gears. I wanted keep these 33"s and to be near 2500-2700 RPM at 80mph.

Im gonna hate running 3300 RPM on road trips. It shouldn't be bad for the motor to run 2-4 hrs straight at that RPM, should it? I just felt a good combo of mpg and less stress on the engine around 2500 rpm on long trips.

I was hoping these new tires would be on this Jeep for a few years, but I'll prob try to get some 285/75r17 or 290/70r17 to go 34" sooner than later, so I can drop those RPMs on long trips by a few hundred.

ON A POSITIVE NOTE:. I'm LOVING THE TORQUE in gears 3 thru 6 now tho. 1st and 2nd are a bit short, so take offs from a stop light are slower, due to having to shift a couple times so soon. But, it's a JEEP 😀 The shop told me not to off-road until I have my break-in and fluid swap done, but I'm sure I'll love it more on the fun terrain.

Yeah the blue color is what you want for a full time trail rig, which is what you're falling in on 33's.

35's would be perfect. You could run 37's if you wanted to.
 
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go with some 315`s or 35`s
Yeah, I found some used 35s with good tread and wheels for pretty cheap in my local classifieds. Maybe I'll get those to run on long trips and swap back to 33s when not road tripping.
 
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Yeah the blue color is what you want for a full time trail rig, which is what you're falling in on 33's.

35's would be perfect. You could run 37's if you wanted to.
I agree with you on 35s. I'd be a bit gunshy to run 37s later if I got more lift tho... I don't want to put unneeded stress on those D30 axles.

Hopefully, my motor will be ok spinning at 3300 for a few hours at 4 to 5 times a year during trips.
 
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I agree with you on 35s. I'd be a bit gunshy to run 37s later if I got more lift tho... I don't want to put unneeded stress on those D30 axles.

Hopefully, my motor will be ok spinning at 3300 for a few hours at 4 to 5 times a year during trips.

lol totally agree on that d30 up front. I'm in the same boat as far as axles go, but have an automatic so 37's aren't really an option anyway.

A mild 2-2.5" lift on some 35's looks great and drives great though imho. I've found it's a very workable compromise for some decent off-road performance but can still daily it no problem.
 
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Update: got a 1500 lb pop up tent trailer recently, prob 1900 loaded on this 1.5 hr trip. It towed great with the 4.56s around town. But...

Holy hell!!! I climb hills in 6th gear maintaining 65-70 and can gain speed up the hill if I shift down to 5th gear on these 4.56s on 285/70r17s. I was about 15mpg... not bad I guess. I couldn't maintain speed before w/ 3.21 with a solo driver up a hill (would've never dared trying to pull with them) .

Now, I'm debating whether to even get 315's, just wondering if I'd have the same or close to the same towing pull. My friend has a mildly use set he's going to sell me soon when he upgrades to 37s. Maybe I'll just put them on another set of rims and just swap.
 
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Update: got a 1500 lb pop up tent trailer recently, prob 1900 loaded on this 1.5 hr trip. It towed great with the 4.56s around town. But...

Holy hell!!! I climb hills in 6th gear maintaining 65-70 and can gain speed up the hill if I shift down to 5th gear on these 4.56s on 285/70r17s. I was about 15mpg... not bad I guess. I couldn't maintain speed before w/ 3.21 with a solo driver up a hill (would've never dared trying to pull with them) .

Now, I'm debating whether to even get 315's, just wondering if I'd have the same or close to the same towing pull. My friend has a mildly use set he's going to sell me soon when he upgrades to 37s. Maybe I'll just put them on another set of rims and just swap.

Yep regearing is a huge difference. You get so used to it being bad that when you do regear it's a palm to forehead moment.
 
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Yep regearing is a huge difference. You get so used to it being bad that when you do regear it's a palm to forehead moment.
I was sold on the regear after the first two months, just had to overcome the pay the price moment 😝
 
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Had 4.56 gears in my XJ with manual transmission, first with 33s, then 35s after the 33s wore out. (Tires were mud terrains.) I drove it everyday and everywhere, including many trips to other states. For awhile, I was commuting between the Grand Canyon and Los Angeles every other weekend so my boys could visit their mother in California. 33s are a great size and had better acceleration on the highway, on the flats and inclines. The larger rolling radius of the 35s were an advantage on the trail. Both sizes are great choices. Because of their performance on the trail, once I went with 35s, I’ve never gone back to 33s.

Currently drive a 2012 Rubicon with 6 speed on 35s with 4.10 gears. She had 33s when I bought her three months ago. If highway performance was the most important thing to me, I’d run 33s. 33s still have good trail performance. The 35s give up a bit on the highway, but make up for it on the trail.

The practical thing to do is run the 33s until they wear out. Save yourself money. Borrow a set of 35s and drive them for a few days. Then you’ll know which size suits your purposes better.

If you’re wondering, my Jeep currently runs LT315R70/17 BF Goodrich KM3 mud terrains. Far out performs BFGs of the past!
 
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