Is 33s on a stock 2006 TJ with 3.73 gears asking for trouble?

If so post the link! I'm obviously a newb lol. I have an SYE brand new in the box sitting in the garage. Waiting to install it until this winter. That and I still need to pick up the driveshaft.

Just FYI...If it's a Super Short SYE you won't be able to change the speedo gear because it's eliminated.
 
  • Like
Reactions: Chris
There are a lot of guys running higher gears and no vibration, there are also a lot that can't get rid of the vibes and have gone with lockout hubs. It is hit or miss.

I have ran 4 different front shafts, two sets of tires, rims, mounts, control arms, axel shafts, 100's of different pinion angles and still have the vibration.

Had I known then what I know now I most likely would have kept a 31in tire on the jeep.
A local guy had the exact same issues with his LJ and the only cure was to install lockout hubs. The LJ just doesn't like something in that combination.
 
What I find so strange about your particular case is how the problem is with the front drive shaft...don't most people's vibration issues after a lift/regear stem from the rear DS?

Don't discount the rear drive shaft as the possible culprit. I re-geared a year ago and immediately got vibes above 50 mph with nothing else changing in the jeep other than gears, and it's not just the auto with the vibe problem. Mine is a 5 speed. I too thought my front drive shaft was the problem, because I could remove it and the vibes got a bunch less. 2 new drive shafts later and still no fix, I focused attention to the rear DS. I removed the rear DS and went for a spin. Low and behold, no more vibes. So this leads me to my current expenditure, A SYE and CV rear drive shaft. Now the jury is still out whether this will solve my vibe problem.
 
Don't discount the rear drive shaft as the possible culprit. I re-geared a year ago and immediately got vibes above 50 mph with nothing else changing in the jeep other than gears, and it's not just the auto with the vibe problem. Mine is a 5 speed. I too thought my front drive shaft was the problem, because I could remove it and the vibes got a bunch less. 2 new drive shafts later and still no fix, I focused attention to the rear DS. I removed the rear DS and went for a spin. Low and behold, no more vibes. So this leads me to my current expenditure, A SYE and CV rear drive shaft. Now the jury is still out whether this will solve my vibe problem.


Been there and done that. The SYE didn't change anything. The problem comes in with the harmonics of both shafts spinning. Since there is no way to stop the rear lock outs in the fronts is the only way to solve the problem.
 
Okay, this thread has thoroughly confused me. Haha.

06 Rubicon Automatic. I'm wanting to switch up to 33s, potentially even 35s (depending on the lift/fenders I grab). Is it 4.56 or 4.88 gears for 33" tires, @Jerry Bransford? What about for 35s?

Most of my driving is around base below 45 (usually at 35) mph though when I do leave base I get up to 60-65 for stretches of 15-30 miles depending on where I'm headed. I don't leave the base often.
 
Okay, this thread has thoroughly confused me. Haha.

06 Rubicon Automatic. I'm wanting to switch up to 33s, potentially even 35s (depending on the lift/fenders I grab). Is it 4.56 or 4.88 gears for 33" tires, @Jerry Bransford? What about for 35s?
For 33's, I'd go no less than 4.88 though I personally would go 5.13. For 35's, no less than 5.13 though I'd go 5.38. My 4.88 gearing with my 35's absolutely sucks on the street and highway with the automatic but that's what it came with after my previous TJ was stolen.
 
What's the exact reasoning here?

Sorry for the 20 questions, I'm seeing things in this thread that I never thought about before, particularly the talk on ideal RPM ranges. For reasons I can't easily define, I've been treating my Rubicon as if 1900-2200 is ideal for the bits of cruising I do up to about 60mph on the highways. It's not one of my old sports cars/imports so I don't run the RPMs up because I know that it's not a fast vehicle, but am I babying it too much?

(I also think I have fuel system/engine issues and need a tune up, 34 miles today and watched the gauge drop more than an 8th)
 
What's the exact reasoning here?

Sorry for the 20 questions, I'm seeing things in this thread that I never thought about before, particularly the talk on ideal RPM ranges. For reasons I can't easily define, I've been treating my Rubicon as if 1900-2200 is ideal for the bits of cruising I do up to about 60mph on the highways. It's not one of my old sports cars/imports so I don't run the RPMs up because I know that it's not a fast vehicle, but am I babying it too much?

(I also think I have fuel system/engine issues and need a tune up, 34 miles today and watched the gauge drop more than an 8th)
At 1900-2200 rpms you are lugging your engine. That will kill gas mileage and the engine. You need to be running above 2,200 at 60 mph.
 
At 1900-2200 rpms you are lugging your engine. That will kill gas mileage and the engine. You need to be running above 2,200 at 60 mph.

I've been trying to find the sweet spot for my Jeep too, and i've always thought that above 2000rpm's was too much if you want good fuel efficiency - ? I say this because the "shift assist arrow" always pops up at around 1900rpms, which leads me to believe that anything above that is not "fuel efficient" in the eyes of whoever programmed this at the factory, and the service manual clearly states that this is a fuel efficiency feature. So which one is correct?
 
At 1900-2200 rpms you are lugging your engine. That will kill gas mileage and the engine. You need to be running above 2,200 at 60 mph.

Explain further? I'm on stock wheels/tires with the stock 4.10's in this thing and 1900rpm is about 55mph for me, 2k being around 60-63.

Most of the driving I do, as I live on a military base and rarely leave it, is between 35-45mph and I'm usually putting around @ 1200-1300rpm.
 
@Nashorn101 & @Shwane as you go up in tire size and stay at the original gearing it throws off the rpms it get the same performance out of you engine. That's why people re-gear when they go with larger tires. As tires go up and gear doesn't change the rpms drag and you lug your engine. That's why you loose your get up and go.

@LCL-Dead You may want to try driving with your O/D off. See how that does for you. And I'm assuming Semper Fi by your location.
 
Interesting, I'm 33's with 3.73's and a 5 speed. Exact same RPM at that speed

That's because the 42RLE automatic has a 9% steeper overdrive, which is about two gear notches, or, in your case, one tire size notch and one gear notch. So, you both have the same crappy 60 mph rpm. Jeep sorely misgeared the 03-06 auto TJs from the factory. Yours was adequately geared until the 33's were slapped on.
 
I've been trying to find the sweet spot for my Jeep too, and i've always thought that above 2000rpm's was too much if you want good fuel efficiency - ? I say this because the "shift assist arrow" always pops up at around 1900rpms, which leads me to believe that anything above that is not "fuel efficient" in the eyes of whoever programmed this at the factory, and the service manual clearly states that this is a fuel efficiency feature. So which one is correct?

The correct rpm for fuel efficiency doesn't really exist. The idea that people have unfortunately created in their head is that more rpm = more fuel. It's understandable that the idea came about since you'd think the more an engine spins, the more fuel it needs, but that isn't correct.

Let's take two Jeeps, one of them doing 2000 rpm at 60 and the other doing 2500 rpm at 60. I would be willing to bet money in nearly every single experiment that the 2500 rpm case would get better gas mileage simply because of the power band of the 4.0. It prefers 2500 to 2000.

Now, let's look away from the power band of the engine and focus on the actual physics of the two Jeeps. There are two advantages to gears: one being that it puts your rpm in the "correct" spot to make all of your transmission gears usable, and the other benefit is that it makes things easier to turn. Take a jeep with 33's on 3.07 and another with 33's on 4.88. Put a wrench and socket on the axle yoke and try to turn the nut, essentially rolling the jeep forwards or backwards. The one with 4.88 will be worlds easier to turn, just as if you were riding a bicycle and peddling in low vs high gears. Now the Jeep doing 2500 rpm has both of these advantages. It's in the power band, but it also has the easier mechanical advantage due to the lower gear setup.

The gas pedal is related directly to your foot via the throttle position sensor, no ifs, ands, or buts about it. Your good or crappy gas mileage comes from how much you push the gas pedal down. If you take the top off and notice less gas mileage, then you had to push your foot further down on average vs when you had the top on. That difference may not be discernible to your foot, but it's there.

So, with the two Jeeps I listed, the driver with the one doing 2500 rpm pushes the gas pedal less because of the easier mechanical advantage that Jeep has due to the gears. The fact that you're at 2500 rpm and right in the 4.0's special spot of efficiency is just an added bonus. 2000 and below is lugging, so you should get less fuel mileage doing 2000.

Back to rpm. People think rpm means more fuel but it doesn't. Since the 2500 rpm Jeep is doing less work, the engine computer gives it less fuel. Sure, the engine may be spinning faster, but the difference is that the fuel injectors are being slowed down as to how much fuel they shoot into the engine. People don't understand this concept, they think the engine shoots the same amount of fuel 24/7 and that if you rev the engine up, that same amount of fuel gets multiplied and wastes tons of fuel. Not the case.

It would be helpful if more people understood the concept. I didn't for a while, but I'm regeared and I can tell you my fuel mileage with 31's went up on 4.10s compared to 3.55, and my accelration is way better. I shift at 4,000 merging on the highway and I get 16-17 mpg going about 70-75 constantly.
 
  • Like
Reactions: UpperMI and StG58
I've been trying to find the sweet spot for my Jeep too, and i've always thought that above 2000rpm's was too much if you want good fuel efficiency - ? I say this because the "shift assist arrow" always pops up at around 1900rpms, which leads me to believe that anything above that is not "fuel efficient" in the eyes of whoever programmed this at the factory, and the service manual clearly states that this is a fuel efficiency feature. So which one is correct?

The shift light is stupid, and your Jeep will feel incredibly gutless. I shift my 4.0 no less than 3,000 in the city.

You're not going to notice a huge difference in fuel mileage between different rpms on the highway, as it's nearly negligible until you reach either a point of having them too high or too low.

The purpose of gears is to bring your performance to normal. I know for a fact that your highway gear with 3.73 and 33's is not fun, I had the same setup with 31's and 3.55. My mileage went up 1 mpg from what it used to be, but the real difference is the performance. Whether the gears help or hurt your mpg, it's not going to make a massive difference over a long period of time. The gears are for performance, if you get mpg gain from it, just consider it an added bonus.
 
The shift light is stupid, and your Jeep will feel incredibly gutless. I shift my 4.0 no less than 3,000 in the city.

You're not going to notice a huge difference in fuel mileage between different rpms on the highway, as it's nearly negligible until you reach either a point of having them too high or too low.

The purpose of gears is to bring your performance to normal. I know for a fact that your highway gear with 3.73 and 33's is not fun, I had the same setup with 31's and 3.55. My mileage went up 1 mpg from what it used to be, but the real difference is the performance. Whether the gears help or hurt your mpg, it's not going to make a massive difference over a long period of time. The gears are for performance, if you get mpg gain from it, just consider it an added bonus.

It's just, it's hard to imagine the shift light being incorrect. I mean, it was put there by the people who built the TJ? At the same time though, I have been thinking about how theoretically more RPM's would mean less work for your engine - and your explanation further emphasized this. Which, is good news to me because i'd love to give it more RPM's!

The other concept that i've been thinking about, is that, theoretically, the lower your gear ratio = the less your rear end is turning per X rpm's, which means more fuel efficiency (albeit with a loss of "get up and go"). But your scenario with the "turning the drive shaft manually" on two different Jeeps with 3.07 gears and 4.88 gears seems to explain this concept better.

In which case, if the higher the gear ratio = the easier it is to turn your rear end = more fuel efficiency and more "get up and go": then why don't factory vehicles come with such high gear ratios like 4.88 or higher? For example, i've heard people complain about the 4.11's on th Rubicon with 31" tires. Why didn't Jeep put in a higher ratio than 4.11?
 
1900 is lugging the engine, not too mention 1200-1300. Hell, idle is about 800.

A couple things come into play. You have to get beyond "getting it back to stock rpm's." It is no longer stock with 33/35 inch tires. They are much heavier, wider, and need more than "back to stock" gearing to keep forward momentum. Plus you are going to be lifted, so you make the "block" we drive even worse.

The 4.0 can run at 2600-2800 all day without a sweat and do very well efficiency wise. Why did Jeep run such high ratios (3.07, are you freakin kidding??) is partially to meet EPA requirements. Not necessarily mpg, likely more for emissions. More rpm's generally mean more emission output. That and many people think 4.11 is low. Mention deep 4.XX gears and many question you; say 5.XX and they think you are nuts. We used to build a bunch of Toyota 8" back in the day and 5.29 to 5.71 were the recommendation. Those guys loved 36" Swampers/Cepeks on the little 22r/5 spd/8" diffs.

To add: scrap those "charts" that are floating around. Again, they are strictly mathematical calculations to get back to stock rpms and in whatever is the 1:1 gear, overdrive is not taken into account.
 
It's just, it's hard to imagine the shift light being incorrect. I mean, it was put there by the people who built the TJ? At the same time though, I have been thinking about how theoretically more RPM's would mean less work for your engine - and your explanation further emphasized this. Which, is good news to me because i'd love to give it more RPM's!

The other concept that i've been thinking about, is that, theoretically, the lower your gear ratio = the less your rear end is turning per X rpm's, which means more fuel efficiency (albeit with a loss of "get up and go"). But your scenario with the "turning the drive shaft manually" on two different Jeeps with 3.07 gears and 4.88 gears seems to explain this concept better.

In which case, if the higher the gear ratio = the easier it is to turn your rear end = more fuel efficiency and more "get up and go": then why don't factory vehicles come with such high gear ratios like 4.88 or higher? For example, i've heard people complain about the 4.11's on th Rubicon with 31" tires. Why didn't Jeep put in a higher ratio than 4.11?

Well like I said, there's a point where it become too much. 31's with 4.88 on a 4.0 engine would just feel really low, too low really. At that point you would be revving quite high when you could easily drop the rpm and still maintain speed. It's at the point that rpm is excessive that it starts to hurt fuel mileage. There's just no need for that much gear on a street driver, so they don't do it that way.

Just to avoid confusion, lower gears are larger numbers and higher gears are smaller numbers. Example: 3.07 is higher than 4.88 and 4.88 is lower than 3.07. It seems you got them switched so I wanted to make that clear or else it gets confusing real quick.
 
  • Like
Reactions: Kyle_W
Well like I said, there's a point where it become too much. 31's with 4.88 on a 4.0 engine would just feel really low, too low really. At that point you would be revving quite high when you could easily drop the rpm and still maintain speed. It's at the point that rpm is excessive that it starts to hurt fuel mileage. There's just no need for that much gear on a street driver, so they don't do it that way.

Just to avoid confusion, lower gears are larger numbers and higher gears are smaller numbers. Example: 3.07 is higher than 4.88 and 4.88 is lower than 3.07. It seems you got them switched so I wanted to make that clear or else it gets confusing real quick.

Ok now I understand. Thank you!


Sent from my iPhone using Tapatalk