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  1. #41
    Senior Member Timmy's Avatar
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    Quote Originally Posted by JeepLab View Post
    When i say "struggled" thats probably not the best word. The Jeep was fine getting to those speeds, but the pressure i had to hold on the pedal to get there was uncomfortable
    That makes more sense, thanks for elaborating on that. And I do totally understand what you are talking about. I was driving down the road this morning at 40mph, with my 3.73 gears, and I had shifted into 5th gear and I was at 1400rpm just to save some gas. The 3.6L has enough power that it could not only maintain 40mph, but I could actually accelerate slightly if I wanted to (and I do mean slightly.) If I needed a hair more power, I downshifted to 4th which brought me to 1600-1700rpm and I could accelerate without much issue. Maybe that's why I'm getting 16.5mpg in my city driving on my 37" tires (and yes, my speedo is calibrated) versus a lot of other guys only getting 13mpg.

    As I was driving, I was thinking about our gearing conversations and how if I was at 75mph on the highway in 6th gear, I would be pissed off that I was at 2700 RPM when clearly the 3.6L can cruise at a much lower RPM. I remember when I had my 35" tires on and I would drop into 6th gear all the time on flat surfaces and cruise at 1700-1800 RPM (55mph-60mph) very happily. 6th gear is suppose to be an "overdrive" gear, not a passing gear, right? I think that's why I see so much conflicting information on the web and when I talk with people. It's like people want 6th gear to be able to accelerate up a descent hill on the highway. Maybe in a little 4 door sedan that has a low drag coefficient you could do that, but in a mobile brick with 37" tires that just doesn't seem a good use of the power band.

    I've gone back and forth on the 4.56 and 4.88 decision. One day I think I want to try the 4.88's, then, like today, I'm thinking I'd be dumb to do that when like you and I want to see my RPM's spinning lower as it is quieter, smoother and more gas friendly. The reality is, on 35" tires, my 3.73 gears were *almost* fine for me. I was mostly happy, wishing I had just a hair more low-end. I probably would have been happiest at 4.10 gearing with those tires. When I calculate out what 4.56 gearing looks like with my 37" tires, it is actually just a hair more aggressive than what 4.10 gearing would have been with my 35" tires. The one thing I'm worried about with the 4.88 gearing is first and second gear. I'm not worried that they would have enough power, but actually that they have too much power and you have to shift out of them too quickly. I really don't want to pull a left hand turn from a stop light having to shift not only through 2nd gear, but possibly all the way to 3rd gear at the exit of the turn. I watched a video of a guy on-line that showed the difference between his 3.73 gears on 35" tires versus 4.88 gears on 35" tires. It was his first drive after getting 4.88 gearing. It was interesting to hear his surprise at how quickly he had jumped up to 4th gear. It was one of those "oh crap, I didn't expect that, hope I didn't make a mistake" type of reactions.

    I think for me, what I'm looking for is that gearing that almost let's me start from a dead stop in 2nd gear. I say almost because I don't want it to be a guarantee in all circumstances, just your usual flat grade, 1/2 second stop with a slow pull out. To me, that would be just about perfect. What I'm basing that on is driving my other vehicles. I've noticed that my other vehicles (all auto's) are calibrated not only in their gearing but also in their programming to actually have you launch in 2nd gear from a stop if the conditions are right. 1st gear is used if it is a full-on stop where you actually sit there for more than 1 second and your previous driving style coming up to the stop sign was more aggressive (because remember, gear programming these days is now adaptive and it knows when you were racing around versus driving like a grandpa.)

    Quote Originally Posted by dalearyous
    i also don't see how you could cruise at 75 mph at 2k rpms. my jeep stock had trouble maintaining 75 because in 6th gear because the RPMs were so low.
    I'm not sure about your experience, but as I said above, I was maintaining 40mph at 1400rpm. I used to cruise at 70mph at 2000rpm all the time and it maintained it just fine. The 3.6L has a lot more torque than people give it credit for. I get tired of reading people say all the time that the engine is useless below 1800-1900rpm. That is just crazy! I can accelerate at high speed from 1500rpm!
    Last edited by Timmy; 03-26-2015 at 12:10 PM.
    2014 Jeep JKU Sahara, Manual - /OlllllllO\ - 4" Metal Cloak lift, 37" Toyo Open Country's on 20" XD Bully Rims, 4.56 Yukon gears, Mopar High Top Fenders, ARB Front Bull Bar Bumper, ARB Rear Bumper, Teraflex HD Tire Carrier, Teraflex Tire Carrier Accessory Mount, Twin Rotopax mount, Hi-Lift Jack mounted on front bumper, Reverse LED work lights, Warn 9.5ti winch, Synergy Drag Link, Trackbar Relocation Bracket, AMP Power Steps, JK1001 Radio, SpiderShade.

  2. #42
    Senior Member Timmy's Avatar
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    Just another follow-up to the book I just published (sorry, I write a lot.)

    For what it's worth, I took a fairly good look at the gearing options from stock, to 35" tires to 37" tires. It is becoming very apparent to me of the following based on RPM vs. MPH vs. Gear (I'm now realizing I'm re-inventing the wheel here, aka, the chart at the beginning of this forum.)

    3.6L JK with 6spd Manual (Auto is probably the same.)
    3.23 Gearing on stock tires = 3.73 gearing on 35" tires = 4.10 gearing on 37" tires (basically a base JK feel.)
    3.73 Gearing on stock tires = 4.10 gearing on 35" tires = 4.56 gearing on 37" tires (basically a JKU with the max tow package feel.)
    4.10 Gearing on stock tires = 4.56 gearing on 35" tires = 4.88 gearing on 37" tires (basically a Rubicon feel.)

    In each case, the gearing is slightly steeper to the 35" tires, and then slightly steeper yet to the 37" tires. It's not by much, about 1% change for each, but that is enough to possibly make up for the difference of the added weight of the tires.

    Maybe the real question we need to be targeting for people is... If you went to a dealer and test drove a base JK, a JKU with the max towing package and a Rubicon, which did you like driving the most?

    The little equation I just posted above is basically what the graphical chart at the beginning of this thread shows, I think it just puts it in a little more in-your-face, easier to digest style as you know you could go to a dealer and experience all three to better understand what you could expect from your Jeep after a re-gear.
    2014 Jeep JKU Sahara, Manual - /OlllllllO\ - 4" Metal Cloak lift, 37" Toyo Open Country's on 20" XD Bully Rims, 4.56 Yukon gears, Mopar High Top Fenders, ARB Front Bull Bar Bumper, ARB Rear Bumper, Teraflex HD Tire Carrier, Teraflex Tire Carrier Accessory Mount, Twin Rotopax mount, Hi-Lift Jack mounted on front bumper, Reverse LED work lights, Warn 9.5ti winch, Synergy Drag Link, Trackbar Relocation Bracket, AMP Power Steps, JK1001 Radio, SpiderShade.

  3. #43

    The Truth about Gears and Tires

    My 13 jk 6 speed equipped with a ripp i had a buddy slap 4.10s in over my old 3.21s and its a perfeft combo i can use 6th as low as 45mph and still have acceleration power at 70 i doing 2200

  4. #44
    Quote Originally Posted by dalearyous View Post
    anyway a lot of this is circumstantial and i have to agree with snarf, drive what feels best. clearly with your setup 4.56 drives best. it would be very hard to duplicate that as i don't know anyone in person that has a turbo or super charger. and maybe you can get away with 4.56 on 37s BECAUSE of the super charger ... or if you have a free RIPP supercharger i would be happy to be a guinea pig
    "Drive what feels best" is no answer at all. Anyone can agree with that. The driver's goals will dictate what feels best, and with gears you rarely know how its going to feel until you've spent the money and ripped your diffs apart.

    Im not against 5.13, please dont take it that way, Tonka, our JK on 40s has 5.13 and no SC and she feels fast. there are different opinions with regard to this related to driving style and location. In NJ you want to be able to drive fast as well as wheel. I also have a 4 to 1 transfer case that gives a little more freedom to run a little less gear.

    the best information is for those of us who have actually done it to share with others what our trucks do mathematically now. Then others can get in their trucks and run their RPM up to where we say ours go to maintain highway speed, and see if thats livable for them.

  5. #45
    I have 5.13s. My 37s measure 35 (KM2) I dont have a rubi, and am not on the highway often. Its the best feeling for my situation, Might be too much gear for others, but when I put it in 4 lo and the truck climbs without me touching the pedals regardless of terrain its worth it.

    Shouldnt drive too fast anyway. No rush.

  6. #46
    That is way out of line with BFG's liturature on their tires which states the tires are 36.8 inch in diameter. I cannot see them having a +/- 1.8inches manufacturing tolerance. I could see +/-.30 manufacturing tolerance at most.

  7. #47
    Quote Originally Posted by Timmy View Post
    3.6L JK with 6spd Manual (Auto is probably the same.)
    3.23 Gearing on stock tires = 3.73 gearing on 35" tires = 4.10 gearing on 37" tires (basically a base JK feel.)
    3.73 Gearing on stock tires = 4.10 gearing on 35" tires = 4.56 gearing on 37" tires (basically a JKU with the max tow package feel.)
    4.10 Gearing on stock tires = 4.56 gearing on 35" tires = 4.88 gearing on 37" tires (basically a Rubicon feel.)
    i like this. this is basically how it was described to me.

    Quote Originally Posted by JeepLab View Post
    "Drive what feels best" is no answer at all. Anyone can agree with that. The driver's goals will dictate what feels best, and with gears you rarely know how its going to feel until you've spent the money and ripped your diffs apart.

    Im not against 5.13, please dont take it that way, Tonka, our JK on 40s has 5.13 and no SC and she feels fast. there are different opinions with regard to this related to driving style and location. In NJ you want to be able to drive fast as well as wheel. I also have a 4 to 1 transfer case that gives a little more freedom to run a little less gear.

    the best information is for those of us who have actually done it to share with others what our trucks do mathematically now. Then others can get in their trucks and run their RPM up to where we say ours go to maintain highway speed, and see if thats livable for them.
    "drive what feels best" as in like what was said, try and find and test drive other peoples rigs and then make a decision. i understand and i am not offended at all. your original post was trying to be informative and point out some glaring misinformation that people use to select gears and i agree with it. i also started this late, on my phone, and just now (on my computer) realize what timmy's rig is and that he does not have a SC. so that explains a bit.

  8. #48
    Senior Member Timmy's Avatar
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    Hey guys, I'm ordering my 4.56 gears today and thought I'd post at how I came to my decision on the gear ratio I selected in the event that it helps someone else out (lookin' at you Pickles, for when you finally upgrade to 37" tires, ba hahaha. See Pickles Tire Decision thread for the background here.)

    My Jeep: 2014 JKU Sahara, 3.6L manual 6spd, 37" tires. Only future upgrade is a new front bumper and winch (around 200lbs. more weight) and possibly a supercharger if things work out.

    First, I'd like to thank some of the forum people here for allowing me to chat with them. I spoke with FerrariFast (FF) and jt1911, who was kind enough to chat with me by phone. Both have rigs with 37" tires, but both were Autos running 4.88 gearing versus my 6spd. Both of the guys love their 4.88 gearing and are recommending I go that direction versus the 4.56 gearing that JL recommends.

    What I have been experiencing overall is that the majority of people making recommendations are running auto transmissions and then broadly indicating their experience should translate just fine for people with 6spd's. Then I keep reading and re-reading what JeepLab has said and experienced, and putting much more weight behind his comments because he is running a manual as well. The reality is, the 6spd's do have a different experience because the gearing is different. It's too easy to focus in on the fact that sixth gear in the manual is close to the fifth gear in the auto and call it good from there. Truth be told, the 6spd has steeper gears from 1st-4th, 5th gear is equal to the auto's 4th, and 6th gear is longer than the auto's 5th gear. If I were to match the axle gearing of someone running an auto, I'd find my 1st-4th gears to be shifting much sooner than they are, all in an effort to say that my overdrive gear is now matching that of an auto transmission. To help demonstrate this, here is part of my discussion with FF. He very kindly sent me the following showing when his Jeep was shifting on his way to 60 Mph.

    Quote Originally Posted by ferrarifast
    Auto Transmission...

    1st gear shifts around 18-20 MPH
    2nd gear shifts around 35 MPH
    3rd gear shifts around 47 MPH
    60 MPH cruising at 2250 RPMs.
    I went ahead and whipped up a formula to calculate what speed my manual 6spd would be at if I shifted at the same RPM as FF with 4.88 gearing and then with 4.56 gearing. (Sorry the formula is not more simplified, it is written this way to dump into my programmable calculator.) His auto is shifting around the same time I personally shift (obviously on a 6spd, shift point is unique per person but I do find in every day driving I typically shift around 3000 to 3200 RPM naturally, which matches what his Jeep was doing.)

    Formula
    MPH = (((([RPM/({Trans Gear Ratio}*{Axle Ratio}))*{Circumference of tire in inches})/12[inches])/5280[feet])*60[minutes]

    Example
    What speed would I be traveling when at 2250 RPM, in 6th gear, with a 4.88 axle on 37" tires (36" measured)?
    61.95 Mph = ((((2250/(.797*4.88))*113.09)/12)/5280)*60

    All calculated with 37" tires, accept the stock Rubicon which is calculated with stock tires.
    1st Gear @ 3100 RPM (FF's shift point to 2nd gear)
    • 4.88 Axle, Auto [3.59:1] - 19 Mph
    • 4.88 Axle, Manual [4.459:1] - 15 Mph
    • 4.56 Axle, Manual [4.459:1] - 16 Mph
    • 4.10 Axle, Auto Stock Rubicon [3.59:1] - 19 Mph

    2nd Gear @ 3500 RPM (FF's shift point to 3rd gear)
    • 4.88 Axle, Auto [2.19:1] - 35 Mph
    • 4.88 Axle, Manual [2.614:1] - 27 Mph
    • 4.56 Axle, Manual [2.614:1] - 29 Mph
    • 4.10 Axle, Auto Stock Rubicon [2.19:1] - 36 Mph

    3rd Gear @ 3000 RPM (FF's shift point to 4th gear)
    • 4.88 Axle, Auto [1.41:1] - 47 Mph
    • 4.88 Axle, Manual [1.723:1] - 38 Mph
    • 4.56 Axle, Manual [1.723:1] - 41 Mph
    • 4.10 Axle, Auto Stock Rubicon [1.41:1] - 48 Mph

    4th Gear @ 2735 RPM (FF didn't provide this, I'm guessing it held 4th to 60 Mph and then it switched to 5th gear once he lifted.)
    • 4.88 Axle, Auto [1.0:1] - 60 Mph
    • 4.88 Axle, Manual [1.2:1] - 50 Mph
    • 4.56 Axle, Manual [1.2:1] - 54 Mph
    • 4.10 Axle, Auto Stock Rubicon [1.0:1] - 62 Mph

    5th Gear @ 2250 RPM (FF's recorded cruise RPM. I also would have held 4th to 60Mph, but I'd skip 5th and go directly to 6th.)
    • 4.88 Axle, Auto [0.83:1] - 60 Mph
    • 4.88 Axle, Manual [1.0:1] - 49 Mph
    • 4.56 Axle, Manual [1.0:1] - 53 Mph
    • 4.10 Axle, Auto Stock Rubicon [0.83:1] - 61 Mph

    6th Gear @ 60 Mph (This shows what RPM I would be at in the manual's overdrive gear at 60 Mph, ie. MPG savings!)
    • 4.88 Axle, Manual [0.797:1] - 2180 RPM (vs. 2250 RPM of auto)
    • 4.56 Axle, Manual [0.797:1] - 2037 RPM (vs. 2250 RPM of auto)


    Just for comparison, here is how fast the 6spd would have been going if I ran at FF's cruising RPM.
    6th Gear @ 2250 RPM
    • 4.88 Axle, Manual [0.797:1] - 62 Mph (vs. 60 Mph of auto)
    • 4.56 Axle, Manual [0.797:1] - 66 Mph (vs. 60 Mph of auto)


    I get what JeepLab was describing now about 4.56's being a nice fit for a 6spd manual. If I ran 4.88 gearing on my 6spd, it's not that it would be horrible or anything, but, it certainly is not the same experience as described by those with autos. The 4.56 gearing is ALREADY a steeper gearing overall for the 1st-4th gears than the autos with 4.88 gears! In other words, it already has more power, I'm already shifting sooner/more, let alone what the 4.88 gears would provide vs. an auto. If the 1st-4th gears are already steeper than those happy 4.88 auto guys, than why not go with the 4.56 vs. the 4.88 gearing and pick up some more fuel efficient high end that is also quieter and smoother at highway speeds? The 4.56 gearing in a manual transmission, with 37" tires, is STILL more aggressive/steeper than a stock Rubicon with 4.10 gears of same transmission (6spd or auto!) New Jeep owners are advised all the time that the automatic Rubicon is a better city driver and not as preferred on the highway as a Sahara if it's your daily driver. Dang! And the 4.56 geared 6spd, on 37" tires, is steeper in 1st-4th than a stock automatic Rubicon, but you get a lower overdrive gear (ie. lower final RPM) than a stock Rubicon!

    So, long story short, I'm going with the 4.56 gears. Obviously everything I wrote here is "science" and real-life might play out different, but I really think that the experience in a 6spd manual deserves a slightly different decision or approach than that of an automatic. The process of doing this research has also really opened up my eyes about all the different configurations you can purchase a new Jeep and what your experience might be in each combination.

    Thanks to everyone for your feedback and lively discussion. I might actually hold off on ordering the gears today if for no other reason that northridge4x4 has Easter Safari kicking off tomorrow, so maybe a deal will come my way ;-) So if you guys look over this and see some error in my work, or decision making, there is still time re-evaluate and make a different decision.

    Regards,

    Timmy!
    2014 Jeep JKU Sahara, Manual - /OlllllllO\ - 4" Metal Cloak lift, 37" Toyo Open Country's on 20" XD Bully Rims, 4.56 Yukon gears, Mopar High Top Fenders, ARB Front Bull Bar Bumper, ARB Rear Bumper, Teraflex HD Tire Carrier, Teraflex Tire Carrier Accessory Mount, Twin Rotopax mount, Hi-Lift Jack mounted on front bumper, Reverse LED work lights, Warn 9.5ti winch, Synergy Drag Link, Trackbar Relocation Bracket, AMP Power Steps, JK1001 Radio, SpiderShade.

  9. #49
    The most important difference auto vs. manual, is in the manual, you can pick your gear. Dont have enough gear? down shift. Too much? up shift.

    The auto guys are more at the mercy of the mathmatics and gear ratios.

  10. #50
    Senior Member Timmy's Avatar
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    Quote Originally Posted by Rexx19 View Post
    The most important difference auto vs. manual, is in the manual, you can pick your gear. Dont have enough gear? down shift. Too much? up shift.

    The auto guys are more at the mercy of the mathmatics and gear ratios.
    Great point, and one reason why I like the manuals! Not to mention I don't have to mess around with getting the transmission re-programmed when changing tire/gear sizes, or changing again when you put a supercharger in. Plus, you get an extra gear that you can decide how best to use (for re-gearing) as either more low-end, or more-high end fuel savings! There are good reasons to buy an auto, but I think there are better reasons to go manual.
    2014 Jeep JKU Sahara, Manual - /OlllllllO\ - 4" Metal Cloak lift, 37" Toyo Open Country's on 20" XD Bully Rims, 4.56 Yukon gears, Mopar High Top Fenders, ARB Front Bull Bar Bumper, ARB Rear Bumper, Teraflex HD Tire Carrier, Teraflex Tire Carrier Accessory Mount, Twin Rotopax mount, Hi-Lift Jack mounted on front bumper, Reverse LED work lights, Warn 9.5ti winch, Synergy Drag Link, Trackbar Relocation Bracket, AMP Power Steps, JK1001 Radio, SpiderShade.

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