Do I need to regear if I get 34” tires on my 2 door Sport S

[CarbonSteel]

Once you drive a properly geared Jeep, you would probably change your mind. The 8 speed does a great job compensating for larger tires and masking the added drag.

I dont know about you but if I pay for 8 speeds, I would want to use all 8 gears.

Not sure I follow what you are saying, but I think you're agreeing with my thoughts.

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[c20040215]

Not sure I follow what you are saying, but I think you're agreeing with my thoughts.

lol
Yes, I was agreeing with you.

 

[jbcrane]

In the short term, probably not. However... if you're in your Jeep for the long haul - yes, eventually you'll probably want to. Just this week I had my 315/70R17's put on my 6-sp MT Sport S (3.6L) up from the stock AT 245/75's. Of course there's a huge difference between the two. I went with the 64 lbs KO2's (C-ply) because they were significantly lighter than the Nitto's I really wanted (.) - and my 6-sp MT will definitely turn them. I haven't driven it too much yet but I do know it'll wear my clutch more. That makes me just a little uncomfortable enough to explore 488's - but don't feel like I need to it immediately. So to your question, eventually yes - you'll probably want to. And BTW - it's totally 1,000% worth it.

 

[Zandcwhite]

I am not calling you or anyone out in particular, this is a general statement that is often made when someone asks "should I re-gear". For those running 4.10's and 37's and 38's that have not had an issue, that would have to be defined. I will step in it again and say those folks are "living with it", but given the choice they would re-gear without hesitation.

My Rubicon is not broken and there are no operational issues, but it is not working as it should be. The engine is not in its proper RPM range and it shows in a number of ways--power, MPG, drivability, etc. So yes, it goes, but is it optimum or even close to optimal ? No way...

The fact of the matter is the 8 speed is such an improvement over all previous wrangler autos that gearing really isn’t an issue. It has 2 overdrive gears, it should downshift out of 8th at the slightest load as designed. There’s no benefit to holding your top gear at any speed regardless of headwinds, hills, etc. If you’re transmission is doing that your vehicle is simply geared too low to see any benefit of the double overdrive. With the 4.7-1 first gear, a JL sport with 3.45 gears is effectively geared the same as a JK with 4.29 gears in first gear. With the second overdrive 8th gear with 3.45’s is effectively a JK in 6th gear with 2.88’s. We truly can have our cake and eat it too. You may prefer quicker acceleration at the expense of higher rpms when cruising 80mph or more, or maybe you never drive over 70mph. Some prefer to stay on the higher side of gearing as it’s still plenty low and allows us to turn much lower rpms when cruising down mountain passes in Utah at 85mph. Both work just fine thanks to all the gearing available in the 8 speed. It’s simple math.

 

[CarbonSteel]

The fact of the matter is the 8 speed is such an improvement over all previous wrangler autos that gearing really isn’t an issue. It has 2 overdrive gears, it should downshift out of 8th at the slightest load as designed. There’s no benefit to holding your top gear at any speed regardless of headwinds, hills, etc. If you’re transmission is doing that your vehicle is simply geared too low to see any benefit of the double overdrive. With the 4.7-1 first gear, a JL sport with 3.45 gears is effectively geared the same as a JK with 4.29 gears in first gear. With the second overdrive 8th gear with 3.45’s is effectively a JK in 6th gear with 2.88’s. We truly can have our cake and eat it too. You may prefer quicker acceleration at the expense of higher rpms when cruising 80mph or more, or maybe you never drive over 70mph. Some prefer to stay on the higher side of gearing as it’s still plenty low and allows us to turn much lower rpms when cruising down mountain passes in Utah at 85mph. Both work just fine thanks to all the gearing available in the 8 speed. It’s simple math.

I am not sure that I can agree with this on a 3.6L. The other engines, no problem, as they develop enough torque to compensate and thus the impact of not gearing is not as big of an issue. However, it is easy to see why you have to re-gear on a 3.6L with 35" or 37" tires. I have had all 3--33", 35", and 37" tires and even with the 33's the engine was not powerful enough to manage hills and headwinds.

Move from sea level to 7K feet and you will see it become even more obvious. The 8 speed can compensate, but only to the degree the engine can tolerate it. When you are not in or able to stay in your OD after a tire change, you are correct, it is simple math--you have reduced the overall gear ratio to the point where the engine is no longer in its operating range and cannot develop the torque needed to stay in the OD gears.

The 3.6L is the most sensitive to this and it needs to be above 2,500 as a minimum at highway speeds to be at the edge of its power range. I am currently running 4.88 and 37's and I should have gone 5.13 to compensate for the loss of power due to altitude. My transmission is not locked in 8th, nor does it need to be, but it does need to be able to go into 8th as it did with 4.88's and 35" tires and many times it cannot. Lastly, I have yet to ever hear of anyone stating that they "over-geared" and RPMs or top speed is an issue. It is always quite the opposite--I should have geared to "X" and "X" is always a lower gear than the one they have.

With all of that said, I have no problem saying again that while people say it will be fine, in reality (especially with a 3.6L) it is not--you need to re-gear.

 

[Zandcwhite]

The

I am not sure that I can agree with this on a 3.6L. The other engines, no problem, as they develop enough torque to compensate and thus the impact of not gearing is not as big of an issue. However, it is easy to see why you have to re-gear on a 3.6L with 35" or 37" tires. I have had all 3--33", 35", and 37" tires and even with the 33's the engine was not powerful enough to manage hills and headwinds.

Move from sea level to 7K feet and you will see it become even more obvious. The 8 speed can compensate, but only to the degree the engine can tolerate it. When you are not in or able to stay in your OD after a tire change, you are correct, it is simple math--you have reduced the overall gear ratio to the point where the engine is no longer in its operating range and cannot develop the torque needed to stay in the OD gears.

The 3.6L is the most sensitive to this and it needs to be above 2,500 as a minimum at highway speeds to be at the edge of its power range. I am currently running 4.88 and 37's and I should have gone 5.13 to compensate for the loss of power due to altitude. My transmission is not locked in 8th, nor does it need to be, but it does need to be able to go into 8th as it did with 4.88's and 35" tires and many times it cannot. Lastly, I have yet to ever hear of anyone stating that they "over-geared" and RPMs or top speed is an issue. It is always quite the opposite--I should have geared to "X" and "X" is always a lower gear than the one they have.

With all of that said, I have no problem saying again that while people say it will be fine, in reality (especially with a 3.6L) it is not--you need to re-gear.

The jk had the same 3.6. It managed hills and headwinds exactly the same as the jl, or any other vehicle for that matter. It's supposed to downshift. That's the design intent. A jk Rubicon with 4.10's has a 1st gear drive ratio of 14.7 to 1. A JLR has a 1st gear drive ratio of 19.27. That is identical to a jk with 5.38 gears. Would you gear a jk with an auto to 5.38's for 35's? Of course not because it only has 1 Overdrive of .83-1. Thanks to our .67-1 8th gear, you could get away with 5.38's and 35's but it would be excessive in my opinion. The big difference I see is the digital dash telling you wich great your automatic transmission is in. The jk would drop a gear at the slightest hill or headwind, to 5th gear which is 1-1. Nobody bated an eye, complained their Jeep wouldn't stay in Overdrive, or claimed they needed 5.13's for 35's. Now your jl shifts into the same 1-1 gear (6th) on inclines, and everyone freaks out, complains they are missing 2 gears, think the jeep should stay in 8th gear all the time, and are ready to go to 5.13's for 35's. The engine doesn't know if the gearing it needs to maintain speed at a given load by raising rpm and therefore power output comes from the transmission downshifting or from running deeper axle gears. Sure running super deep gears will keep you in the higher transmission gears for a given load, but you'll also be running much higher rpms than necessary at light loads as your deep gears have effectively eliminated the Overdrive. 5.13 gears in 8th gear have the exact same rpms as 4.10 gears in 7th. All you've effectively done is turned 8th gear into 7th gear. Personally I'll stick with 4.10's and 2150 rpm at 85mph vs 5.13's and 2650 rpm at 85mph with 37's, but to each his own. Thanks to the massive gear spread either way works.

 

[CarbonSteel]

Personally I'll stick with 4.10's and 2150 rpm at 85mph vs 5.13's and 2650 rpm at 85mph with 37's, but to each his own. Thanks to the massive gear spread either way works.

2150 at 85 means you would be at 1800 or less at 70, which with a 3.6L you would lugging the engine so badly you would be lucky to stay in 6th. It does not work--you obviously don't have a non-ESS 3.6L.

2650 at 85 is nothing, it is not even 50% of the usable RPM range. I am at 2400 at 85 with 4.88 and 37's and wish it was 2650.

As you said, each to his or her own...

 

[Zandcwhite]

2150 at 85 means you would be at 1800 or less at 70, which with a 3.6L you would lugging the engine so badly you would be lucky to stay in 6th. It does not work--you obviously don't have a non-ESS 3.6L.

2650 at 85 is nothing, it is not even 50% of the usable RPM range. I am at 2400 at 85 with 4.88 and 37's and wish it was 2650.

As you said, each to his or her own...

2.0t does help quite a bit with the torque delivery. 4.10's and 37's at 70mph it will definitely drop to 7th under any load, but even pulling a grade it holds 6th no problem at ~2600 rpm. Of course coming down a pass, it will roll 70 in 8th at 1750rpm and average 30+ mpg doing it, if only we could drive everywhere down hill...

 

[CarbonSteel]

2.0t does help quite a bit with the torque delivery. 4.10's and 37's at 70mph it will definitely drop to 7th under any load, but even pulling a grade it holds 6th no problem at ~2600 rpm. Of course coming down a pass, it will roll 70 in 8th at 1750rpm and average 30+ mpg doing it, if only we could drive everywhere down hill...

Agreed; the 2.0T and 3.0D are not plagued with this cr@p. I am confident the reason that FCA came out with the E-torque 3.6L was to try and compensate for the gutless torque curve it produces. They should have twin turbocharged it instead--problem solved.

I am waiting to see if the 3.0TT Tornado will find its way into the Wrangler...I may be shopping for a new one if that happens.

 

[Bigdave18629]

I know this is an older thread, very informative, great debate, but left me on the fence about 35,s on stock 3.6 Willys. Have a chance to pick some up cheap

 

[entropy]

I know this is an older thread, very informative, great debate, but left me on the fence about 35,s on stock 3.6 Willys. Have a chance to pick some up cheap

Pick up the tires. Drive it and if it bothers you, regear.

 

[Zandcwhite]

I know this is an older thread, very informative, great debate, but left me on the fence about 35,s on stock 3.6 Willys. Have a chance to pick some up cheap

If they are cheap enough, you can sell them if you really don't like it and don't want to regear. There's only one way to know for sure what works or doesn't for you and that's to try it for yourself.

 

[Carlton]

I know this is an older thread, very informative, great debate, but left me on the fence about 35,s on stock 3.6 Willys. Have a chance to pick some up cheap

if it is an auto, you will be fine. Get a Taser and call it a day.

 

[Tncdrew]

I know this is an older thread, very informative, great debate, but left me on the fence about 35,s on stock 3.6 Willys. Have a chance to pick some up cheap

Like others have suggested, pick up the tires and try them out. If you're happy with the result, all is great.
I can tell you one thing though, going from the stock 32" Willys tires on a 3.6L, to 35's, you WILL lose some of your Jeep's performance (it's physics after all).
For many of the reasons @CarbonSteel has offered on this topic, I'm in the process of re-gearing my Willys to 4.56, (and I'm only increasing tire size to 33").
I've been underwhelmed with my Willys' 3.45 gear performance from day one.
I guess I'm just one that refuses to "live with it".
Good luck!

 

[Bigdave18629]

Like others have suggested, pick up the tires and try them out. If you're happy with the result, all is great.
I can tell you one thing though, going from the stock 32" Willys tires on a 3.6L, to 35's, you WILL lose some of your Jeep's performance (it's physics after all).
For many of the reasons @CarbonSteel has offered on this topic, I'm in the process of re-gearing my Willys to 4.56, (and I'm only increasing tire size to 33").
I've been underwhelmed with my Willys' 3.45 gear performance from day one.
I guess I'm just one that refuses to "live with it".
Good luck!

I am pretty underwhelmed by the JLU performance in general, but I knew what I was getting into. I seriously thought about the 392 for that reason. I have my fast car, my wife has our comfortable car, so I am really just looking for a third personality for the driveway. The set up I am looking at is a BFG that according to specs is 34". My intent was not go above 33's on this......but we all start with intent.

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