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4.10 vs 4.56 RPM w/ 35s @ 70mph (HWY Driving)

78K views 153 replies 46 participants last post by  nycgags 
#1 ·
If you are running a JK2012+ 4.10 or 4.56 gear with 35" Tires what is your rpm at 70mph? Please specify your Tire Size and Brand. Also, if it is at all possible don't forget to add your psi levels.

I'm in the midst of deciding if I should upgrade from a 3.21 to a 4.10 or 4.56. I will be installing a set of 315/70/17 Duratracs on my JKU2013. Since this is a daily driver / weekend warrior I need to have the best of both worlds.

What are your suggestions and lets see these RPM results!

Cheers!

Conrad
 
#3 ·
The general consensus of the Forum Members has been, 3.6 engine, with 32s, or 33s, go with the 4.10 ratio. 3.6 with 35s, go with the 4.56.....:thumb:
 
#4 ·
I have a 2012 JK. 6 speed manual. 4.56 gears. 315/70R17 Duratracs.

I run about 2500 RPMs at 70 on the freeway. Figure around 2250 if you substitute 4.10's.
An automatic will run around 2650 with 4.56's and 2400 with 4.10's.

Both choices would be fine for a 2013. When I was looking to get rid of my 3.21's I went with 4.56's because they were a little cheaper and easier to find than 4.10's. The difference in RPMs on the freeway wasn't enough to really tip it in either direction.
 
#5 ·
Holy Smokes!

You really think the (Auto) w/ 4.56 @ 70mhp will be running over 2600rpm? I was leaning toward the 4.56 re-gear..however, running that high kinda scares me. How much more wear do you think that is on the engine? and what would you say your gas mileage is?

I was hoping to stay in the green zone at cruising speeds.
 
#6 ·
Quite honestly, I hate running in the "green zone" on my tach. The 3.6 is gutless below 2,000 RPMs. When I had 3.21 gears and stock 255/75R17 tires I wouldn't even bother running in 6th gear unless I was headed downhill with a tail wind. The mileage between 5th and 6th was the same but I had more power in 5th.

The 3.6 was designed to be in it's happy place in the mid 2,000's. It performs great in that range. I can hold 70 in 6th gear going up the mild hills we have here in the flat farm lands of fly-over country. And this engine will have no longevity issues with running at that RPM range all day long. Modern engines, properly maintained, will give you hundreds of thousands of miles of trouble free driving. That is, if there aren't any manufacturing defects of course.

Quite frankly, your mileage is going to stink when you put 35" tires on a Jeep with the aerodynamics of a brick wall. The difference between 4.10 and 4.56 is going to be basically nothing. Maybe 1% difference. If that. Driving 60 MPH instead of 70 will make more difference than everything else combined simply because of aerodynamics.
 
#8 ·
Derf and 338 Lapua,

What I don't get is how 4.10 (auto) is running at 2700rpm and the 4.56 (manual) is running at 2500rpm @ 70mph with 35s.

Is there potential that if I put 4.56...on my auto it could bump me up to 2900rpm?
 
#10 ·
Different people will get different results for several reasons. Inflation pressure affects tire diameter. The computer setting for your tire diameter can impact it as well. When I calibrated my computer for the new tires, I matched it to the GPS. I ended up telling the computer the tire size was 33.48". If I used the advertised diameter of 34.6" the speedometer would be off and I would tell you a different RPM because I wouldn't really be running 70 MPH.

Don't forget too that the factory tach may be off.

Lapua's numbers seem off to me as well. It doesn't make any sense that he's seeing 2400 at 65 but 2700 at 70. I would expect if you're seeing 2400 at 65 that you'd see 2600 at 70. Well, unless his lockup torque converter doesn't lock up at 70 but it does at 65 (which doesn't make a lot of sense).
 
#9 ·
It depends on the gear ratio of the final overdrive gear in the trans. I am not sure what 6th gear is in the manual vs 5th gear in the auto. Normally auto's will turn a higher RPM given everything equal due to the torque convertor...but I am assuming the auto in the Jeep has a torque convertor lock-up when in OD to help with mileage.
 
#15 ·
4.56s all day long OP. Nothing wrong whatsoever with 4.10s but X2 on everything Derf said in Post #6 especially:
Quite frankly, your mileage is going to stink when you put 35" tires on a Jeep with the aerodynamics of a brick wall. The difference between 4.10 and 4.56 is going to be basically nothing. Maybe 1% difference. If that. Driving 60 MPH instead of 70 will make more difference than everything else combined simply because of aerodynamics.
People fret over MPG and highway RPM but remember you're comparing two gears that are very similar on a not-very sensitive engine and tranny. Have a friend drive your Jeep on the highway in 5th. Close your eyes. Have him/her hit 2500 RPM and 2700 RPM respectively. I'll bet $$$ you can't tell the difference. I'll even take that bet up until about 2900 RPMs and you still won't hear any difference in engine noise. 200 RPMs (if that) difference between 4.10s and 4.56s won't do jack to MPG or engine noise. Get 4.56s- you'll have more pep, can pass on the freeway and have better crawl.
** I will take exception to Michigan...if you regularly drive/commute @ 80 MPH you are at about 2900 RPMs on 4.56s....IMO this is just where you get more engine noise.
The other option: find a Rubi on 4.10s and 35s at a dealer near you and drive it. Not possible for some but in my area I can find several.
 
#16 ·
I have a 2012 auto, 4.10 gearing and 315/75 R16 tires, 1/4 "-1/2" ( IIRC ) shy of a true ( if there's such a thing ) 35 " tire. I just got back from a 300 mi. trip yesterday. At 70 mph, it was turning 2300 rpm, The computer is flashed for a loaded tire height of 33.50 " inflated at 25 psi.
MPG when I got home was at 17.6 and still climbing. FWIW. This was all hwy. driving and the MPG "calculator" hasn't be reset for months.
 
#19 ·
I went with 4.10s, but currently have the stock 32s on. It's feels perfect. If I was going to 35s, I would have gone with 4.56. I'm very impressed with the fuel mileage I'm getting, it's really no different than with the 3.21s. What I did notice was the heavy 33s I had really affected the mileage far more than the regear did. I sold them, and am shopping for a lighter set, not only for the mileage, but the ride was terrible as well.
 
#20 ·
I'm going to have a complete front axle with 4.10's available out of my 2014 jk in about 7 weeks ( having a Dynatrac prorock 44 made for my front) if anyone in my area is interested. :happyyes:
 
#22 ·
I have a 2014 JKU Rubicon Auto with 4.10s and 35/12.5/17 Nitto Trail Grapplers running at 33 psi. I'm not sure what the RPM is at 70 but I will look tonight and post back. I used a Superchips Flashpaq after installing the tires and ran the Fuel Saver tune for my first tank and checked the mileage manually at 15.5. I have no problems with the power at all and have now changed to the 87 octane tune to check the mileage and I will have to say it did add a little more kick to the throttle. I have not ran 4.56s or ever been in a Jeep that has them but for now I have no reason to regear because my 4.10's satisfy my need very well. The only reason I could see myself getting a new set of gears is when I start adding some weight. I am running an extremely light weight rig right now without a spare and I'm not sure if the extra weight of bumpers, roof rack, spare tire, ...ect will affect my performance or not.
 
#23 ·
My 2013 ruby with 315/75/16 and the stock 4.10 turns about 2500 at 70 and I get about 17.5-18 mpg. If i slow down to 65 then its about 2250 rpm and 19-19.5 mpg.. I know this because i just took the 5hr trip from baltimore to Bantam and even with all the hills I still squeaked out 17.8.. Personally i feel this combo to be perfect for a 2dr..
 
#26 ·
I'm not trying to hijack the thread, just a quick question. My brother has a 2014 sahara jku w/3.6l auto, and wanted to go up to a 35 in tire. He was told to regear to 5.12's and I'm seeing a lot of people saying 4.88's. how wil re-gearing to taller gears effect performance, gas mileage? Are 5.12's correct for his application? since it is an auto tranny.
 
#28 ·
X3.
5.13s were the common gear ratio for 35s on the 3.8L. Someone is giving his "old" advice. Overkill on a JKU Pentastar UNLESS he wants a (very) low crawl ratio or plans to go to 37s. 4.56s or 4.88s are the best option; with most people going 4.56s, some 4.88s and some 4.10s for MPG. (as covered in this thread).
Now that I have 4.56s I realize 4.88s would've been fine- but I want the most out of that engine & tranny and don't care about MPG.
 
#31 ·
Hi guys, here's another guy asking this question again I'm certain, lol

I've decided to spend the $ and go for a re-gear of the axles.... 2014 2-door JK Willys, OEM 3.73, auto and DuraTrac 315/70R17, do I go 4.10 or 4.56?

Will 4.10 give me enough power increase from 3.73, bang for buck?

Will 4.56 cause to much engine revving noise @ 70 MPH on the freeway, calculation says ~2600 RPM?

Seeking replies from the knowledges and experienced ones!

Em...
 
#32 ·
Changing from 3.73 to 4.10 gears will increase engine RPM at highway speed by about 150 RPM. You're not even going to be able to tell the difference at highway speed. Just starting off, from a dead stop, will be noticeably better with 4.10s vs 3.73s, ... for about a week, until you get used to it.
 
#33 ·
glad I found this thread because I am turning in my JKU for regearing this week plus arb install

I went with 4.56 because 90% of the time I run my 33's on a 2014 JKU manual thinking ide be running 2500 RPM right?

and the rest of the time 35's crawling during the summers what you guys think?

good thread
 
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