What gear ratio should I install in my Jeep Wrangler TJ / LJ? (and other re-gearing FAQs)

[kevnls]

But

Just buy a Speedo Healer and don't worry about gears.

What in the dear loving world of Billy Mays State-Fair-demo products is that??

**researching**

 

[Captain Phoenix]

What in the dear loving world of Billy Mays State-Fair-demo products is that??

**researching**

How to calibrate your speedometer using SpeedoHealer by HealTech | Jeep Wrangler TJ Forum https://share.google/3K1kpldmy1CYLnKiO

 

[kevnls]

What in the dear loving world of Billy Mays State-Fair-demo products is that??

**researching**

Oh yeah I dunno about that. I'm trying to keep my Jeep free of any more additional circuit boards rather than adding more of them.

 

[Captain Phoenix]

What in the dear loving world of Billy Mays State-Fair-demo products is that??

**researching**

https://ebay.us/m/SS6YsV

Though it appears to be out of stock here.

 

[Captain Phoenix]

What in the dear loving world of Billy Mays State-Fair-demo products is that??

**researching**

HealTech SpeedoHealer Plug-n-Play Kit for 98-06 Jeep TJ Wrangler, 04-06 Jeep LJ, 98-01 Cherokee XJ | POLY PERFORMANCE https://share.google/2JT6M0uL1ASVAnicb

 

[Captain Phoenix]

Oh yeah I dunno about that. I'm trying to keep my Jeep free of any more additional circuit boards rather than adding more of them.

Gears are only a "close enough" fix, this is a perfect fix. It's also universal so any time you change tires or air pressure it can just be reprogrammed.

 

[machoheadgames]

Update (I'm sure this will help so many people sleep at night again). I did the 4.88 swap on this raging squirrel machine and it feels like the right call. It's a bit more shifting for cruising around town, but why do you think I bought a 6-speed manual if I don't love shifting? New question though. Speedo-gear. I think it's looking like a 41 based on this chart https://www.novak-adapt.com/catalog/transfer-case-parts/np-speedometer-gears/. Does anyone have any experience with this on an '05 4-banger with 31" tires and an NV231 transfer-case?

The factory would have used a 43 tooth for that setup, though the speedometer wouldn’t be accurate (but the odometer would). For accurate speedo, 41 would be about right.

The factory used speedo drive gears that generated a perfect odometer, with the speedometer being about 4.5% fast.

If I’m deciding between speedo healer or the gear, I’m going with the gear if I have no future plans to change anything. I think the gear is a bit more reliable/simple. But, you get your money’s worth pretty quickly out of the electronic solutions if you’re going to change plans ever.

 

[kevnls]

The factory would have used a 43 tooth for that setup, though the speedometer wouldn’t be accurate (but the odometer would). For accurate speedo, 41 would be about right.

The factory used speedo drive gears that generated a perfect odometer, with the speedometer being about 4.5% fast.

If I’m deciding between speedo healer or the gear, I’m going with the gear if I have no future plans to change anything. I think the gear is a bit more reliable/simple. But, you get your money’s worth pretty quickly out of the electronic solutions if you’re going to change plans ever.

Thanks!

Oh yeah I'm actually not terribly concerned about the money. I bought the last year of what I consider (in my mind) to be a Jeep for a very specific reason. If I have to buy a new speedo-gear every time I change tire-sizes no biggie. I do not want an electrical short to knock out my speedometer though.

 

[machoheadgames]

Thanks!

Oh yeah I'm actually not terribly concerned about the money. I bought the last year of what I consider (in my mind) to be a Jeep for a very specific reason. If I have to buy a new speedo-gear every time I change tire-sizes no biggie. I do not want an electrical short to knock out my speedometer though.

To be fair, the electronic solutions are pretty proven….but I too prefer the adjusting-at-the-gear setup.

 

[Rickyd]

Update (I'm sure this will help so many people sleep at night again). I did the 4.88 swap on this raging squirrel machine and it feels like the right call. It's a bit more shifting for cruising around town, but why do you think I bought a 6-speed manual if I don't love shifting? New question though. Speedo-gear. I think it's looking like a 41 based on this chart https://www.novak-adapt.com/catalog/transfer-case-parts/np-speedometer-gears/. Does anyone have any experience with this on an '05 4-banger with 31" tires and an NV231 transfer-case?

A chart may or may not work for you. You need actual tire size not advertised. You can use a GPS app on your phone to find actual speed of lets say 60mph. compare it to the dash mph to find a percentage it is off. Apply that percentage to your current speedo gear to find the right tooth count. Correct by macho's amount if you prefer a correct odometer?

 

[machoheadgames]

A chart may or may not work for you. You need actual tire size not advertised. You can use a GPS app on your phone to find actual speed of lets say 60mph. compare it to the dash mph to find a percentage it is off. Apply that percentage to your current speedo gear to find the right tooth count. Correct by macho's amount if you prefer a correct odometer?

Most all of the 31’s I’ve driven end up right at 29.5” actual, so assuming he’s in that range, the 41 would get him an accurate speedo. 43 is how the factory would have equipped it, following their logic. Which is to have the correct odometer and a speed buffer. The charts muddy the waters because you never know what actual size tire was used and you don’t know if they prioritized speed or distance. Most tend to care only about speed, but I kinda like the factory logic so I usually offer both suggestions.

But yeah, in this case doing the math would be an easy way to determine the correct percentage to adjust by for accurate speed.

 

[Captain Phoenix]

I do not want an electrical short to knock out my speedometer though.

A SpeedoHealer is not connected to the Jeep wiring outside of the wires that run the signal from the gears to the PCM so I'm not sure where a short would come from that would affect the SpeedoHealer. I would imagine you're more likely to fry the PCM than the SpeedoHealer but do whatever you like best.

 

[mrblaine]

A SpeedoHealer is not connected to the Jeep wiring outside of the wires that run the signal from the gears to the PCM so I'm not sure where a short would come from that would affect the SpeedoHealer. I would imagine you're more likely to fry the PCM than the SpeedoHealer but do whatever you like best.

You say that now. We've fixed more than one that came in on a tow truck due to no start, no crank, no bus symptoms. The problem is the wiring from the Speedohealer got melted and pulled the PCM down to a no communication status due to the short.

 

[akajibio]

I wanted to make a thread about recommended gear ratios to help out fellow TJ / LJ owners. My reason for this is because we see this question come up all the time, and it could be helpful for new owners to have a thread like this to reference. Those "gear ratio" charts you see floating around the internet are notoriously inaccurate, especially when you consider that they don't take two of the most important factors into consideration: which engine you have, and which transmission you have. Those factors are absolutely crucial (along with tire size) when making a decision on which gear ratio to go with.


6 Cylinder Engines
Keep in mind that the deepest gear you can put in a non-Rubicon model Jeep is a 5.13, while the deepest gear you can put in a Rubicon model Jeep is a 5.38. This chart only covers up to 35" tires, and the primary reason for this is because with 37" tires or larger, you should no longer be running stock axles at that point, and therefore your gear ratio limitations will change. The table below is laid out by tire size in the left hand column, and transmission on the top row. Match up your transmission with your tire size to determine the appropriate gear ratio.

	32RH	42RLE	AX15	NV3550	NSG370
30"	3.73	4.56	4.10	4.10	4.10 / 3.73
31"	3.73	4.88	4.10	4.10	4.10
32"	4.10	4.88	4.46	4.56	4.56 or 4.10
33"	4.10	5.13	4.56	4.88	4.56
34"	4.56	5.13 5.38 (Rubicon models)	5.13	5.13	4.88 or 4.56
35"	4.56	5.13 5.38 (Rubicon models)	5.13	5.13	5.13 or 4.88

4-Cylinder Engines
Generally speaking, it's not a good idea to go over 33" tires on the 4-cylinder engines. For off-roading purposes it's fine, but if you plan on doing any highway driving, anything larger than a 33" tire on a 4-cylinder is really going to make life miserable. The table below is laid out by tire size in the left hand column, and transmission on the top row. Match up your transmission with your tire size to determine the appropriate gear ratio.

	30RH	42RLE	AX5	NV1500	NSG370
30"	4.10	4.56	4.56	4.56
31"	4.10	4.88	4.56	4.56
32"	4.56	4.88	4.56	4.56
33"	4.56	5.13	4.88	4.88
34"	5.13	5.13	5.13	5.13
35"	5.13	5.13	5.13	5.13

Which transmission does my Jeep Wrangler TJ / LJ have?
For information on which transmission you have in your Jeep Wrangler TJ or LJ, please see this post.

Which engine does my Jeep Wrangler TJ / LJ have?
For information on which engine you have in your Jeep Wrangler TJ or LJ, please see this post.

Which axle gear ratio did my Jeep Wrangler TJ / LJ come with?
If you need help determining which gear ratio you currently have, see this thread here: How do I determine my axle gear ratio?

What RPM do I want my TJ to be at at highway speeds?
Ideally you want your engine to be above 2000 RPMs on the highway. The 4.0 for instance doesn't really start it's power band until past 2000 RPM, so keeping it under 2000 RPM at highway speeds is detrimental to performance, and it can also be bad on your engine (in terms of carbon build up, poor fuel economy, etc.). Do not listen to anyone who tells you that you should be crusing at highway speeds with your RPMs under 2000 RPM. This is completely inaccurate and bad information. I prefer mine to be around 2300-2500 RPM at 65 mph, which I feel is the sweet spot for both fuel economy and performance.

What's with 5.13 and 5.38 gears?
5.38 gears will not fit in any other axle other than the Dana 44 axles. In many cases, 5.13 is recommended above for 35s, when 5.38 would actually be a better choice. However, unless you have a Rubicon model (that has both a Dana 44 front and rear axle), then you will have no choice but to use 5.13 gears, unless of course you swapped in Rubicon axles. Many of you will have a Dana 44 rear on your Sport, Sahara, or special edition model TJ. The issue with that is that while you could fit 5.38 gears in the rear Dana 44, they will not fit in your front Dana 30 axle. Remember, that front Dana 44 axle ONLY comes on Rubicon models.

Do I need to have matching gear ratios in both front and rear axles?
Yes! Your front and rear gear ratios must match! If not, you will do serious damage to your vehicle (unless of course you never engage 4WD, in which case, technically you'd be fine.

How much does re-gearing typically cost?
I've found that re-gearing typically costs anywhere from $1000-$1600 for the labor. I've had it done twice, and each time paid $1200 for the labor. This of course excludes parts. You should expect to pay around $500-$800 for parts in addition the labor.

Which brand of gears should I go with?
I personally always recommend Revolution gears, as they are very highly regarded and run by many of us. The general rule of thumb though is to go with whatever gears your installer / shop will warranty. Often times shops will not offer a warranty on certain brands of gears they have never installed before. For this reason, if you really want Revolution gears, but the shop will only warranty Yukon gears, the smart thing to do is go with whatever the shop will warranty.

Is there a break-in procedure for new gears?
Yes, there is indeed! Though Revolution has recently started making REM finished gears that do not require any break-in period whatsoever. In this case, you want to ask the shop installing the gears what they recommend for break-in procedure, and follow their recommendations to the T. Be very aware that if you do not follow the break-in procedure, there's a very good chance you will damage your gears and have to have them replaced. Those break-in procedures are there for a reason.

Should I attempt to install new gears myself?
Absolutely not. If you are reading this, it means you've likely never done it before, and you shouldn't start with learning to wrench by installing gears. Ask someone like @AndyG what happened when he attempted to install his own gears. This isn't to say you couldn't teach yourself to do it, but if you plan on getting it right the first time having never done a gear install before, you'd better think again! This is one of those tasks that takes a lot of skill and experience, as there are a number of variables that all need to be very accurate.

Is there a gear ratio calculator I can play around with?
Yes, there is indeed! Check out the Grim Jeeper Gear Ratio Calculator. It's a very helpful tool that will allow you to see how a given gear ratio will affect your Jeep.

Chris is there anything wrong with running 4.56 gears with 35s for my daily driven 4.0 TJ?

 

[mrblaine]

Chris is there anything wrong with running 4.56 gears with 35s for my daily driven 4.0 TJ?

I'm sensing a trend here.

 

[Mr. Bills]

Is there anything wrong with running 4.56 gears with 35s for my daily driven 4.0 TJ?

Ill advised would be a better term.


When I purchased my '06 LJ Rubicon it had 4.88 gears and 35" tires. It was a dog on anything but level ground, and even on level ground it was apparent that the jeep was undergeared for 35" tires.


One of the first things I did was re-gear to 5.38.

 

[akajibio]

I'm sensing a trend here.

Yes, questioning is a trend. Wanting to know why is also a trend. Intelligent people question everything, Sheep just follow! Sorry if questioning offends you! I thought the whole point of such forum was to exchange ideas and learn.

 

[jjvw]

Chris is there anything wrong with running 4.56 gears with 35s for my daily driven 4.0 TJ?

Still on the search for confirmation bias?

 

[akajibio]

Ill advised would be a better term.


When I purchased my '06 LJ Rubicon it had 4.88 gears and 35" tires. It was a dog on anything but level ground, and even on level ground it was apparent that the jeep was undergeared for 35" tires.


One of the first things I did was re-gear to 5.38.

Thank you Mr. Bill

 

[Captain Phoenix]

Yes, questioning is a trend.

No, the trend is people not reading the thread and asking a question that's been answered and explained in detail already. There's 23 pages in this thread but you're too lazy to read it and want it answered again just for you.