Whether or not you off-road in your Jeep, you will eventually catch the Jeep bug, and you will find yourself suffering from "Lift Envy." Lift Envy is a disease that causes Jeep owners to lust after higher lifted vehicles with bigger and bigger tires underneath them every time a "superior" Jeep drives past. But what the heck is a lift, and what is involved in going bigger? This article explains it all.

Going Big: Upsizing Your Wheels

A lot of people purchase their Jeep thinking they will never go off-road, and that they will have no interest in building it up into a bigger, higher-performing vehicle. When I bought mine, I passed up some great deals because I was convinced I just wanted it for its ability to go topless and for the sporty ride. I had no idea that after a year of owning it that I would be building it up and doing all of my own service.

Eventually, you are probably going to want to get bigger tires for your Jeep. On a stock Jeep, something is just wrong with having that big square box sitting on those little tiny tires and wheels. It looks like it could just tip over. As you can see, the wheel wells on a Jeep Wrangler TJ are quite large, and can handle a bigger tire than the one that comes on it stock. But there is a lot you need to know if you are going to get bigger wheels. Maybe not just for the look, but also to get a wider stance to reduce rollover risk, or maybe to increase clearance for better off road performance!

In exploring my options for going bigger, I've taken some photographs of other Jeeps, so I can copy a look that I particularly like, and I've done a lot of reading about tires, wheels, axles, gearing, body lifts, motor lifts, suspension lifts, wheel alignment, steering straightening, driveshaft replacements, and other topics which all surround getting bigger wheels under your Jeep.

Before we start, here are the bottom lines that we will be working around:

Bigger = Worse Economy - as you move away from stock size tires, your mileage will go down. We will talk about how much later on.

Bigger = Exponential Cost Increase - If you want to go a little bigger, you can just get bigger tires. If you go just a little more big, then you end up buying rims and tires. A little more, and you are replacing springs, shocks, drilling a hole to move your trackbar, and buying rims and tires. A little bigger yet, and you are performing surgery on the driveshaft and transfer case, replacing just about every component in the front steering assembly, and replacing the gears in your differentials. Eventually, expenses can go over the $4,000.00 mark if you go big enough. Further on we discuss just what you have to do to go bigger and bigger.

Big Tire Curve - There is a curving line that says what you have now is too small, and that somewhat bigger tires will be better, but beyond a certain point, bigger tires have diminishing returns, and you've now gone too big. Keep in mind what you will be doing with your car. Do you want to pick up your boss at the airport in a suit while driving on 40" tires lifted up 10" like some sort of off-road competitor in a Jeep that sounds like a motorcycle, or would you rather retain some qualities of a regular car?

The Big Tire Curve shows us that for each of us personally, there is a moderate size tire which will produce the highest possible level of fun for us by not costing too much money in upgrades, pushing our vehicle's tolerances too far, and by not consuming too much gas.

Tire Sizes

Before you consider anything else, learn about tires. Tires for your Jeep TJ come in two different types: Passenger Tires and Light Truck or Floatation Tires. What's the difference? Passenger tires have a softer ride, but are less heavily constructed to withstand abuse. Light Truck tires are tougher stuff but offer a less comfortable ride. Mostly the difference is in the sidewall. A soft, thin sidewall makes the tires softer to ride on, yet more vulnerable to damage.

For some dumbass reason that I cannot fathom to save my life, passenger tires are generally measured using a metric system that is very confusing. Despite my extensive education in geometry, algebra, trigonometry, and calculus, I find the metric system of sizing tires to be almost incomprehensible. Some all terrain tires are also measured using the metric system. I shy away from them because trying to understand exactly what I am getting is difficult when measured using such confusing measurements.

The stock tires that come on a Jeep TJ are P225/75R15 tires. That means they are 225mm wide, 75% of the overall width makes up the sidewall, and they require a 15 inch wide metal wheel rim to be properly mounted. Some less expensive Jeeps come with P215/75R15 tires, which are almost a half inch skinnier, but otherwise identical. These are passenger tires, and despite any sort of trail-rated badge your Jeep might have on it, these tires are not very good for off-roading. Mine were Goodyear GSA's, a standard passenger tire. Two of mine have popped in a year, so I don't think much of Goodyear GSA tires.

Does the graphic above make it make more sense? Heck no, it does not. Who is the bozo who thought up this system? Here's my answer: Who cares? There is a better method of determining tire sizes, just like there is a better way than the metric system to measure distance. Her Majesty's Imperial System of Measurement. God Save The Queen.

31x10.5x15 is a measurement that is easier to understand. Using this system, you can hear a measurement and know exactly how it will look in your mind. And since if you do any tire upgrading to your Jeep, you are going to be buying light truck tires, also called floatation tires. And, thank you God, these tires are typically measured using the Her Majesty's sensible system, although some are not. The tire is 31" tall, 10.5" wide, and needs a rim 15" tall. It's that easy. Some familiar tire sizes:

P215/75R15 - Stock passenger tires. The smallest, skinniest, most sad little dish plates ever screwed onto a Jeep. Shameful. Please do replace these with something - anything other than what you have. Your Jeep looks like a big box skiing around town.

P225/75R15 - Stock passenger tires. These figure out to be around 28.5x8x15 in Imperial measurements. They are pretty small, but they give a soft ride and the Jeep doesn't have to work at all to push them or stop them.

30x9.5 - These are the tires you get if you opt for the off-road optional package for your Jeep. It's kind of strange, I think, that Jeep stealerships offer off-road tires as part of an add-on package instead of offering them as part of a stock vehicle. Most new Jeeps roll off the lot not equipped at all for off-road service, despite being all "trail rated."

31x10.5 - These are the largest tire that will fit on the stock rims (which are 15x7, usually) on your average Jeep Wrangler TJ without any modifications. A few people report that the tires rub some of the suspension components at this size, but that replacing a simple washer on the steering bump stops solves the problem. Loss of fuel economy and power is slight and relatively unnoticeable.

32x11.5 - These are the largest tires that a Jeep Wrangler TJ can fit without a lift installed. For street use only, you can fit these tires under your fenders. If you plan to go off-road at all, you will need a 2 inch lift of some kind. Rims with sufficient backspacing (discussed later) are needed as well to keep these tires from rubbing suspension components. After installation, you will experience a small loss of fuel economy, perhaps 1 or 2 mpg, and loss of power is somewhat noticeable, but not severe. Now you might notice braking is more difficult.

33x12.5 - The darlings of the off-road and mall crawler communities, these are the big tires that have that fat appearance and stick out. Even for street driving, you need a lift of some kind to fit them as well as rims with plenty of backspacing. A few have reportedly stuff these into their wheel wells without a lift before, but even going over railroad tracks could be damaging to the vehicle. I wouldn't recommend this. Loss of fuel economy is significant - 2 ~ 4 mpg, and loss of power is significant. Depending on your engine and the gearing of your axles, you might find this tire size to be nice to look at but a pain to drive on. Braking is definitely more difficult at 33".

35x12.5 - Not the biggest tire ever put on a Jeep, but definitely a really big tire, and typically, as large as someone goes who uses their Jeep on streets, but not always. This size tire really requires a significant and expensive suspension and perhaps some body lift to use on the road. It also requires a heavy-duty axle, known as a Dana 44, in the rear. The typical stock Dana 35 axle might snap under the strain of trying to drive these big meats around. Loss of fuel economy is very significant 4-5mpg. Loss of power probably may require regearing axles in order to find Jeep usable even on the street. You may consider high-performance brakes in order to improve stopping. Regearing your axles will be a necessity.

Bigger and Bigger - Some guys put on 37's, 38's, 40's, or even 44" tires in extreme cases. I don't recommend these tire sizes for a Jeep that will be used to commute any real distance on roads. Fuel economy, power issues, and braking almost require major upgrades in the thousands of dollars to axles, gearing, brakes, suspension lift, brake line extension, and possibly high maintenance of after-market components. Don't forget Death Wobble becomes more likely.

The bigger you go, the more you have to do to your Jeep to make it ready. A complete list of preparations is at the bottom of this article. I should note that the Rubicon usually sits on the lot wearing 31x10x16 tires. Note the 16. The Rubicon comes with 16" rims mounted on it. The usual Jeep TJ is rated at 15mph city and 19mpg highway. With 35's, 10mpg in the city would probably be cause to smile. That's worse fuel economy than a heavy duty pickup truck.

So, tire size is a trade off. You have to look at what you will use your Jeep to do, and balance the clearance and performance you get from bigger tires with fuel economy and having to deal with lost power, which could mean slow starts and difficulty ascending hills. I am no off-roading expert, but what I have observed is that people who just want bigger tires for infrequent but occassional off-roading get 31's. People who off-road a little more get 32's. Guys who are hooked on off-roading and have money to burn seem to prefer 33's or 35's.

Tire Styles and Brands

Being Jeep owners, we want to get some sort of tire for off-roading. After all, this is a Jeep web site, not a web site for wasting time and money making little cars noisy, low to the ground, and basically useless so that Jeep owners laugh at them.

What kind of off-road tire to get? There seem to be several favorites out there. Tire styles seem to come in four different flavors for off-roading. There are All Terrain tires, which are good on the street, OK in the dirt, and crummy in mud. There are Mud Terrain tires which are great in mud, very noisy on the street, and a bit slippery on wet pavement. Generally all terrain tires have smaller tread with grooves, and mud terrain tires have big lugs and spaces so that mud can be cleared out as the wheel turns.

Balance seems to be the key. You must have some idea of what you want your tires to do in order to get a set that will perform well for you. No tire does it all well. If the tire is good on mud and the street, it also has a weak sidewall. If the tire is good in the mud with a strong sidewall, it is probably no good on the street. If a tire is excellent on the street, in the mud, you will just spin them uselessly, going nowhere. So, predict your use, and get an appropriate tire.

Below I highlight some of the tires that I have seen recommended repeatedly. I focused on tires that would be good both on the street and good enough in dirt or mud. There are myriad tire options out there, and this list is not exhaustive, but there is not a bad tire listed below.

Goodyear MT/R - This tire is very popular among Jeep owners, and it is very expensive. The MT/R stands for Maximum Traction, and this tire will set you back some serious coin at $180.00 each. People report getting very high mileage with it, and that it tends to perform pretty well on streets and off road, and even in mud, even though it is not a mud tire, technically.

For looks, the Goodyear MT/R has a very aggressive tread pattern. Recently, DC started putting these tires on Jeep Rubicons as the stock tire. I have never heard anyone who owns these complain about them, even for street use.

BF Goodrich AT/KO - The heavy sidewalls in this tire make it very popular amongst off-roaders who do a lot of street driving. The tread is very reliable on the road, although it won't go too far in heavy mud. A very popular, tough, and reasonably priced tire.

BF Goodrich MT/KM - This is a mud terrain tire that is a little more noisy on the street and less reliable on wet pavement than the AT/KO, but performs quite well by reports if you sipe it. Siping is a process through which the heavy tread lugs in the middle of the tire are cut half-way through their depth by a tire shop to create groove in them. This increases their wet pavement performance greatly, and if done correctly, does not alter tire life. However, siping can void a tire warranty. BFG's are always popular among Jeep enthusiasts, it seems.

Before purchasing a set of mud terrain tires with huge lugs on them, call around to find a local shop that does siping, if you plan to ride these on regular pavement. Many tire shops won't even know what you are talking about when you say "sipe", so you want to make sure you can find a place that can sipe your tires for you before you haul off and stick these on your Jeep.

Procomp MT - Procomp's MT is very popular among some folks because of the relatively reasonable price as compared to the Goodyear MT/R, the aggressive looks, and the fact that unlike most other mud terrain tires, they are relatively quiet to ride on. The big lugs in the middle are even pre-siped, making this tire perform pretty good on wet streets, too. But, here's the downside: the side plywall is only 2 layers, unlike BFG's three layer walls to protect against blowouts on the trail from sharp sticks and rocks. This is a great "looking like going off road" tire, and it isn't that bad out on the trail, either.

There are a bazillion different tires out there. Other companies make tires that Jeep enthusiasts love to death, but these seem to be the big four recommended by people most often on the exper hangout JeepForum.Com. The trades offs between tires seem to be expense, road noise, tread siping, durability, and appearance.

Where to Buy - While buying tires online these days is certainly affordable, wiser men have recommended that we buy tires locally so that we can inexpensively take advantage of warranties and guarantees. Returning a tire that is mounted on your wheel to an online shop? May as well just buy a new tire. So, buying locally is recommended.

Wheels (Rims)

If you are going to go big, you not only need to pick out the size of tire you want to run and the kind of tire you want on your Jeep, you also have to figure out what sorts of rims you want. And, unfortunately, this too is a mini-rocket science sort of endeavor that frustrates and confuses people who just bought a Jeep and yet never before in their lives paid attention to what kind of tires they had on their car.

Let's get started. For those of you who would never dare ask this, wheel rims are the metal thing that the tire is stuck on. The tire is held on by its inflation pressure. If it is deflated too far, it might come off. Pressure of inflation is measured in pounds per square inch (psi). The stock P225/75R15 tires that came with my Jeep are supposed to be inflated to 33 psi.

When you go off-road, usually you air-down your tires to make them softer and create more surface area to contact with the ground. Usually Jeep enthusiasts seem to average between 18 and 25 psi for off-road purposes. Back on the road, they must re-inflate or they will get terrible gas mileage and a squishy, soft, unresponsive ride quality.

Wheels are usually measured in terms of how tall they are, and how wide they are. Typically, Jeep stock ECCO wheels are 15x7. Most people seem to upgrade to 15x8 wheels. Jeep's upgrade RAVINE wheels give you 15x8 wheels. Rubicons come with MOAB wheels that are 16x8.

Stock Jeeps generally come with 15x7 rims with 5.5" of backspacing. Backspacing is important because the less there is, the more the wheel sticks out from the axle and the fender well. The wider the tire you purchase, the less backspacing you need to get in a wheel. A stock Jeep can take a 31x10.5 tire on a 15x7 rim with 5.5" backspacing without any modifications.

If you wish to run 32x11.5 tires, without a lift, you will need rims with less backspacing - maybe 4.5" down to 3.75" of backspacing would be a good idea with a 15x8 rim. Vehicle lift compensates somewhat for the potential for a tire to rub against components vertically, but when you turn the steering wheel, to prevent a wider tire from rubbing up against something important and ripping the tires to shreds, you have four options:

• Modify your driving habits so you never turn the wheel too far (yeah, right!)



• Add washers to the steering stop bolts. There are little bolts on the joint assembly that serve to stop the wheels from turning too far. You can unscrew these, put in a few washers to make them stick out more, and screw them back in to extend your steering stops to prevent rubbing.



• Less backspacing. Buying new rims is the best option. Besides, I like the look of wheels sticking out from a Jeep, and it increases the width of the stance of the Jeep, lessening the chance of rollover if you don't lift up too high.



• Wheel Spacers. Spydertrax produces an excellent wheel spacer. You remove your wheel, screw on these spacer gizmos, and then screw your wheels back on. The result is that you can use your old rims without buying new ones with much larger tires. Spacers usually remove 1.25" of backspacing when applied. This allows Jeep enthusiasts who have invested in the very attractive Canyon or Ravine 15x8 wheels with 5.5" of backspacing to run them as if they had 4.25" of backspacing.

Any time you reduce backspacing by buying new rims or by adding wheel spacers, you increase the load on the axles by putting the wheels farther out from the center of the vehicle. This is typically mentioned as putting extra wear and tear on the wheel bearings, but so many Jeep enthusiasts do it without too many issues, that most don't worry about this.

If you decide to get new rims, like I did, get the right amount of backspacing for your application, and remember that Jeep TJ rims require a bolt pattern of 5 on 4.5". That means there are 5 lug nuts, and they are 4.5" apart from each other. Any other bolt pattern will not fit on your Jeep at all.

And here you were thinking that you could just slap on any old rims you might find for sale. Sorry to make it more complicated, but maybe it saved you some trouble.

Steel vs. Chrome vs. Alloy - And now I am going to make it just a little more complicated. There are different kinds of wheel you can get to go with your new, bigger, meaner, more manly tires. You can opt for steel wheels or alloy wheels. Alloy wheels are very durable in that they don't ding very easily, and they sure do look all shiny and pretty under there. Steel wheels, on the other hand, can be repaired. Most serious off-roaders prefer black steel wheels, the cheaper the better, and they call them "steelies."

You can also get chrome covered steel wheels, but the chrome can chip off, and they rust, and they are no cheaper than alloy wheels. The price differences are amazing. Chrome costs almost the same as alloy, but has none of the benefits and is susceptible to damage. Black steel might be 1/5 the price, (less than $45 in some cases), and while they might rust, who cares? They are easily replaced!

Lifts

The last thing you need to know about your Jeep is about lifts. Once you have decided upon a bigger tire size, a tire brand and style, a wheel (or keep what you have/get a spacer), and you have figured out everything you need to about what you will do with the tire - be it fuel economy, wet road grip, mud performance, or whatever, then you are ready to find out what kind of lift you will need to fit the tire under your Jeep TJ Wrangler.

Lift is measured in inches.

31x10.5: 0 - 2" of lift. None required, some like 2" with it for serious off-roading. Your choice. Feel comfortable going without a lift.

32x11.5: 2 - 3" of lift. None required, but without any lift, no off-roading for you without rubbing problems. Definitely you need less backspacing to handle these wide tires, and 15x8 rims.

33x12.5: 3 - 4.5" of lift. 3" is generally considered the minimum lift to run 33's safely. It can be done with 1-2" of lift, but you're likely to have problems and off-roading you will more than likely get some laughs as you encounter problems. Most report that 3" seems to do the trick. Serious off-roaders and rock-crawlers seem to prefer 4.5". 15x8 or 15x10 rims with 3.75" of backspacing seems to be pretty standard.

35x12.5: Another inch of lift over 33x12.5 requirements is reported to do a pretty good job by most. Some go even higher.

Lifts come with risk. First of all, the higher you lift your Jeep, the more unstable it becomes. Of course, getting wheel rims with less backspacing increases the width of the stance to make it more stable, but as you go up, you cross a line where good stability lies and enter an area where the Jeep's chances of rolling over become significantly greater.

A stock vehicle has a relatively narrow and tall shape, making it somewhat unstable. Putting on wider tires with no lift and wheels with less backspacing will result in a wider stance and more stability. Lifting the Jeep a little returns the center of gravity to a normal position. Lifiting it considerably more can make it less stable.

For every inch upward you go, in order to maintain the same stability, you will need to have your wheels 1 inch farther out on each side. If you move the wheels wider without lifting the Jeep any, you increase stability. If you add larger tires without a lift, that still lifts the height of the Jeep, so more width is desirable. But once you reach 3.75" of backspacing, you've pretty much gone as wide as you probably should, so any increase in tire size or lifting of the Jeep you do will decrease stability an increase the danger factor for rolling the Jeep over.

Lifting a Jeep is the art of adding hardware to it so that the fender flares are up higher in the air so that bigger tires can fit under it. There are two ways to accomplish this: a body lift or a suspension lift.

Body Lifts

There are 11 places on a Jeep TJ where the body of the vehicle is bolted to the frame. There are rubber disks about an inch thick in each of those locations which cushion the body when the Jeep is bounced around. A body lift consists of loosening those bolts, removing them, and lifting up the body of the Jeep to insert spacers in between the rubber disks and the body. The spacers look like black plastic cylinders about two inches in diameter. Then you bolt it back up and your Jeep is lifted.

In order to make everything fit correctly following a body lift, you need to put in a new bracket for your radiator fan shroud, since the shroud is attached to the body, and the radiator is attached to the engine, the body lift moves the shroud so that cooling could be affected. Most body lift kits come with a new bracket.

You also need to move the transfer case control bracket. There is a bracket underneath the body that holds the transfer case control handle in place, and it needs adjusting to make it stick up through the floor board properly. These are not difficult operations that require a mechanic. Someone with a floor jack and some basic mechanics tools should be able to do this on his own just by reading directions online.

Advantages of a body lift are:

Installation Woes. Suspension lifts are very tricky purchases. Many companies do not deliver everything that you need to install them properly in their kits. That includes the big name brand companies. For example, if you are going to install a 3.5" lift on a Jeep, you probably need new shocks, new springs, new wheels, new tires, new adjustable track bars front and rear, and a transfer case lowering kit or a 1 inch body lift with a 1 inch motor mount to straighten out the drive line. You will need new sway bar links front and rear. Lastly, you will possibly need to have an Slip Yoke Eliminator performed on your transfer case output shaft and a new CV (shock absorber type expanding and collapsing) drive shaft installed. You might even need new adjustable forward control arms to restore caster to your alignment and prevent a rough ride, and you'll definitely need to perform a front end alignment.

Good luck finding someone who does all of this correctly and inexpensively.

Whatever you do, consider that your mileage will go way down as you increase tire size. That seems to be more and more important these days with gasoline up over $2.00 a gallon. And also remember the increased wear and tear on everything in your drivetrain. Putting big ass tires, wheels, and lifting a Jeep puts a huge strain on it - it will last fewer miles for you in the long run. The more you modify your Jeep to become a better off-road vehicle, the worse it will perform on the highway, the more dangerous it will be to drive, and the higher risk of rollover you will run. As a final annoyance, big tires are hard to push, so different gears may be necessary, and that can cost $1500 to have done to both axles (you cannot do just one axle or 4WD is impossible). Read on to learn about that.

When selecting the type of lift, get what you need, not what someone else needs you to get to make themselves feel better.

The higher the suspension lift, the more you must modify various items on your Jeep to accomodate it.

3/4" lift, you are only putting coil spacers on the tops of your front springs, usually to raise the front end after having added a winch to the front bumper. Winches and plates weight in around 100 pounds total or more, so when you add one, the front begins to sag about 3/4". This is the simplest, most mild lift possible.

With a 1.75" lift, you are only putting coil spacers on the ends of springs, and perhaps some new shocks could be added, but maybe not. This is usually referred to as a Budget Boost. Pull out the springs, put on the spacers, maybe install some longer bump stops, put everything back together, and you are done.

A 2" ~ 2.5" lift usually consists of shocks and spring replacements. You might also need to install a rear adjustable track bar or drill new holes to put the current track bar back in place. The track bar is a fixed length bar connecting the frame to the axle to keep the axle from floating around to the left and right. When you lift up the Jeep, the angles change, and the axle is now off center and the wheels are over to one side. You can also get an adjustable track bar which can be dialed to longer and shorter to pull the axle back to the center. You will also need new sway bar links for this lift. Preferable some that connect and disconnect easily by pulling and replacing a pin instead of having to use two wrenches to pull out a big bolt. The Jeep may get vibrations from the rear differential gears not meeting the drive shaft's pinion at the right angle. Lower the transfer case skid plate a little with some washers to correct this.

3" of lift is more severe and may involve more component changes. Now the driveline is almost certainly affected. Consider an SYE or lower the t-case a lot. New springs, shocks, swaybar links, and trackbars are needed now. At this height, your Jeep is now better off the road than on the road, and vehicle balance has been lost between the two types of driving. Also, you cannot space your wheels out 3" on each side, so geometry has changed enough to seriously increase the risk of rollover in an accident.

4.5" of lift is very high, and the driveline is definitely impacted. You will need front and rear adjustable track bars, coil springs, and you will very likely get a CV driveshaft and an SYE kit to perform a driveshaft replacement. The cost for this lift is quite high, and the risk of rollover is significant as well. This much lift is usually used for 33" tires. If you want to run 35" tires, you will need a new rear axle, because the Dana 35 (such as my rear axle), is not really capable of pushing a 35" tire down the road without breaking eventually.

There are higher lift kits, but from what I have observed, the few that go this far add another inch of body lift on top of 4.5", and they stop there before becoming very extreme. Besides, our purpose is merely to understand these lifts and what is involved, not to document all possible lift affects or learn how to install them.

 

Regearing

When you put bigger wheels on a Jeep, the number of times the wheel rotates around fully to go the same distance is reduced. That throws a few things off. The first thing is that your speedometer no longer knows how fast you are going. It usues the differential gear ratios and the size of your tires to compute your speed. Also, with significantly bigger tires, you lose power, because the ratio of the gears in your differential are now too "tall", that is, they are designed for a smaller wheel, and the engine has trouble delivering everything it has in the right proportions.

What's it like? Well, someone with tall gears with big wheels in a manual transmission will find that 5th gear act like you are trying to start off in 2nd gear from a dead stop. It will lug and strain and you will have to downshift to get power. Also, you'll be a little slow off the starting line - 1st might feel like it has become 2nd gear.

Jeeps come with differentials geared at the following ratios. You can find out what yours is by crawling under the rear end of your Jeep and looking at the tag on the rear differential. It will have the ratio on it along with some other numbers. Look for one of these ratios: 3.07, 3.55, 3.73, 4.11, 4.56, 4.88, 5.13. The gears in your axle are dependent upon the axle itself, the size of the tires your jeep came with, the transmission, and which engine your Jeep has. A bigger engine with an automatic might use 3.73 comfortably. A smaller engine with a manual might come with 4.56 installed.

In order to regear, you must change the ring and pinion gears in the front and rear axle. If you change only the rear axle, you cannot put the Jeep into 4WD any longer. The gears in front and rear must match or something will break or bind up. Doing your own gears is rare, and labor costs seem to be nearly $600 per axle in most places.

Speedometer and Computer Modifications

Now that you know about axle gears, consider the speed sensor on your transfer case. Manual transmission Jeeps and automatics before 2003 can replace the speedometer gear in the transfer case in order to restore shift points and the speedometer to normal. This is an easy switch out that even an idiot like me can perform. Speedometer gears cost less than $30 at the stealership. Basically you unbolt the sensor, pull off the gear, stick on the new one, replace it, and bolt it back on. Not hard, huh?

The question is, which speedometer gear to get? The below chart should be some help to you. The part number is 520676 plus the two digits in the matrix next to your axle ratio and your tire size. The two digits are also the number of teeth that the gear has in it. I haven't included all gears or tires here. Who knows when to stop? This page mostly is help for novices, so someone who is getting 44" tires installed wouldn't be reading this wondering what gears to get from someone like me. I don't even have big wheels on my Jeep. But here is the help for you, nonetheless.

This table of gears is of no use to Rubicon owners. If you own a Rubicon, the transfer case does not use a gear to determine speed. Intead, it has a pure electronic sensor, and you must have the computer reprogrammed by the dealership in order to have your speedometer readout corrected after you up or down size your tires. In Winter of 2005, I called four local stealerships in my area to have this priced. The price for reprogramming ranged from $42.50 to $87.00. The lowest price was from a Chrysler dealership that does not sell Jeeps. Yes, they can work on your Jeep, too.

Axles

The stock axle set up, like on my Wrangler X, is a Dana 30 in front, and a Dana 35 in back. What's the difference? The Dana 35 is designed to be a rear axle, and it is heavier-duty than the Dana 30 in the front. The rear axle is the one that takes a beating, so Jeep offers an optional upgrade to an axle called Dana 44. If you have a Dana 44 in the rear, you've got a nice, heavy-duty axle for driving big, fat tires and doing serious off-roading. You probably also have better gears.

It is possible to swap out one axle for another. Some people fit Dana 44 axles front and back, or they get even heavier axles off of Chevy pickup trucks and stick them under their rigs in order to do serious off-roading.

How Do I Know Which Axle I Have? If you have a Jeep TJ, you have a Dana 30 in the front and either a Dana 35 or a Dana 44 in the rear. If you bought a Rubicon, you probably have a Dana 44. If you bought a Sport, you might have a Dana 44 or a Dana 35. If you bought an X, and you didn't ask for a Dana 44, you probably don't have one. But there is an easy way to tell.

Crawl under the rear of your jeep and look at the rear differential. A Dana 35 has a rubber plug in the drain/fill hole. The Dana 44 has a metal plug that you unscrew like the one in your Dana 30 in the front. Rubber plug? Dana 35. Sorry. I have a Dana 35, too. Most of us don't have a friggin' clue about axles the day we finally decide to purchase a Jeep Wrangler.

Rubicon Differences

If you are still thinking about getting a Jeep Wrangler, remember to get one with a Dana 44 in it. Yes, it's important later on. In fact, get a Rubicon. Just about everyone who shops for Jeeps ends up thinking they are all the same, then they go out on the Internet and find out that the Rubicon is almost totally different vehicle with upgraded everything.

Rubicons stand about 2.25" taller than your stock Jeep Wrangler TJ Se, X, Sahara, or sport. They have 1" longer coil springs in them, as testified to by the people who raid wrecked Rubicons for their coil springs to boost their Wranglers up a bit more. They also come with 31" tires on them. And, they come with 16x8 wheels instead of 15x7.

Consider that the tires are 2.5" taller, and so offer the axles 1.25" of lift off of the ground. That's 2.25" inches total more height for the fenders and bumpers, and 1.25" inches more clearance for the differentials as compared to a regular Wrangler.

Rubicons also come with a heavier duty transfer case with lower, more powerful gearing. It has heavier axles with lower, more powerful gearing. The stance is a little different, as the axles are wider. The Rubicon's transfer case also is pre-equipped with an SYE, and is more flexible in terms of driveline angles. And the axles contain air lockers that are activated from the dashboard switches, which allows the axles to be locked or unlocked dynamically. Overall, it is a better vehicle to start off with, but it costs a fortune.

Now that you know what is involved, as a novice, you are ready to think about upgrading your tires. You now know what you need to know in order to start making decisions. You know some tire recommendations, you know how size affects your speed, and you know how size can affect power and fuel economy. You know that backspacing on wheels and lifting the Jeep may be necessary as tires grow taller and wider, and that there are costs and advantages to all of this. You can now make informed decisions, and do extra reading, and post messages in the Jeep Forums and ask for more details from more experienced people than I.

Now you know why people say that Jeep stands for Just Empty Every Pocket.

Feedback

Mark writes:

Just wanted to say your web site is awesome. As someone with a 01 Wrangler and a 16 year old son pushing to put "huge" tires on it, I found your information invaluable. Thank you so much for taking the time to write an informative and interesting article on Jeep modifications - both pro and con. So much for the 35's.... I now will not rush blindly into making uninformed decisions. Thanks again!!!!

Online Resources

Goodyear MT/R - Goodyear's page for their MT/R tire. I don't link to the home page because I have Goodyear GSA's on my Jeep, and I think they stink. One popped after only 10,000 miles because I rubbed it on a curb at slow speed in a parking lot. While the GSA model stinks, imo, the MT/R is reported to be the shiznit of tires.

BF Goodrich - The home of a great tire manufacturer for Jeep tires.

Everything You Ever Wanted to Know About Wheels - This amazing site is where I learned just about everything I know about wheels. What a fantastic explanation of bolt patterns, backspacing, offset, and other features of rims for your Jeep.

4WheelDrive Hardware - sells the Spidertrax wheel spacers. Search their online catalog for them.

SpiderTrax Spacer Install - A good example of installing the spidertrax spacers and how they work.

4x4xplor.com - Excellent write ups on mods for a TJ including how to install a body lift and suspension lifts. Very nice.

How To Change Your Speedo Gear - This is a great Stu write up of swapping out the speedometer gear.

All about Speedo Gears - A great article about upgrading your speedo gear.

Adjusting Your Steering Stops - Pictures of steering stops and how to adjust them to keep tires from rubbing at full turn.