Jeep Modifications for off-road trails

JEEP = Just Empty Every Pocket

Basic Modifications

Trail Ratings thru 6 or 7
Old thinking was to start with body armor, Rocker Panel Guards, Skid plates etc. Current thinking is to start with lift for larger tires, lower gears, stronger axels and locking differentials, so you don't need the body armor.

Front and rear tow hooks. $50
Sway bar disconnect. $90
CB radio and a high-quality antenna $150. (See also radios below.)
A GPS and be able to report your location accurately is is invaluable in an emergency.
Small lift kit ($900) and slightly larger, more aggressive wheels ($140-600) and tires ($600).
4.5" lift kit with upper and lower arms ($1,400)
Rocker Panel Guards (rock rails/ rock slider) (best)($120-$325) (Shrockworks, AEV Rocker Guards)
Warn or Sun Performance are good.
Optional - Skid plates:
The factory TJ comes with skid plates for the transmission and transfer case and gas tank. Most people do not install differential skid plates as they reduce your ground clearance. You should learn to plant your tires on obstacles to avoid contact with the differential.
- You can get a gas tank skid plate, that provides better protection around the edges, which will go over the existing one.
- A belly up skid plate ($325) can add 2" of clearance at the transmission and transfer case, but can make the driveshaft angles severe. This requires fine tuning to eliminate drive shaft vibration. (e.g. trailquest.com/teraflex/)

See: Trip Checklist
Top 10 mods at Glen's Jeep,

Configuration for the Rubicon Trail

Requirements for Organized Trips

Company (1)	Pietschmann		Jeep Jamboree USA	Jeepers Jamboree	Albright
Company (1)	Basic	Best	Jeep Jamboree USA	Jeepers Jamboree	Albright
Tires	33"	35"	≥ 31" "C" rating 3-ply sidewalls †	≥ 33"	≥ 33"
Lift	(proper based on tires)		max. 5"	≥ 3.5"	≥ 2.5"
locker	Some rear locker	ARB front & rear			Y
rear gears	3.73	4.88
crawl Ratio	40 manual 27 auto	75 * manual 50 auto
skid plate (2)	std	std	std + oil
rock rails			Y
Side step	N	N		N
Tow hooks (F & R)			Y
Full sized spare (within 3")			Y
CB Radio			Y
winch					Y
Hi Lift jack					Y
Ice Chest			Y

1. See Trips at the Rubicon Trail Page for information about companies doing trips.
2. The Wrangler comes with transfer case and gas tank skid plates standard. An oil pan skid plate may not be required on TJ with proper lift.
† - Goodyear Wrangle AT/S with 2-ply Durawall&tm; would be allowed, but 3-ply is preferred.
* 4:1 transfer case (Rubicon) plus 4.88 differential.
Other recommendations by trip companies:
- It is highly recommended that someone in your group have a winch.
- We suggest that you bring a 5-gallon can of gas per vehicle.
- Acceptable vehicles for Jeepers Jamboree: Jeeps®, Toyota Land Cruisers, Land Rovers, older Broncos, Toyota pick up trucks and other 4x4 vehicles.
- The Rubicon Trail is a pretty mean trail. So, expect some scratches and dents depending on how well you drive.

Rules & Regulations for Calif. 4WD Clubs Sierra Trek. Some additional rules they have are:
- Spare tire with diameter within 3 inches of existing tires (no temporary spares)
- 71" maximum width of body, cage, and/or non-flexible flares.
- 80" maximum overall width sidewall to sidewall. (TJ width with 10.5 tires is 71")
- Antenna(s) must not exceed 4'6"
- Fire extinguisher with gauge indicating good/full, appropriately stored.
- Tow strap or rope (recommend rated at 2 times the vehicle weight)
- Electric fans reduce load on the engine

Basic Recommendations from other sources:
Engine: 6 cylinder recommended. Torque-to-weight ratio is what counts. ≥ 20:1 is inadequate and < 10:1 is overkill.
1997 Wrangler Specs.

Engine	Torque lb-ft	Weight	Ratio
4.0 litre 6 cyl	222	3229	14.5:1
2.5-litre 4 cyl	140	3092	22:1

The 4L engine generates about 90 percent of its peak torque at its 600-rpm idle speed.
Transmission: There is a long standing debate in the four-wheeling world over automatic vs. manual transmissions. For most people automatic is superior. With the manual it is difficult to maneuver at low speed on obstacles due to riding the clutch. Popping the clutch Gear selection is not a problem with an automatic.
One comment on a forum said: "The manual is fun when you start out, but once you step up to bigger, scarier things, you almost want an auto because of the control you have only having to use two pedals. I can't count how many times I've slipped the clutch just barely too much and lost a line because of it."
However, if you have a high crawl ratio (higher gear ratios in the transfer case and differential) your manual transmission behaves mucn like an automataic;
An automatic may slip at low RPM with a high crawl ratio, so some consider Some people use a Two footed driving approach to go over obstacles with an automatic transmission.

Where Manuals Are Better:

Downhill engine braking.
Holding the truck in a specific gear for specific conditions.
No extra engine cooling system load caused by radiator tranny cooler for automatic.

Where Manuals Are Worse:

With tall axle/t-case gears that would cause excessive clutch slipping.
Much harder on drivetrain parts, transferring shock loads and generally breaking parts more often.

Where Automatics Are Better:

Where very fine control is needed.
Where smooth upshifts and downshifts are needed to control traction and maintain momentum.
Gives the driver less to do and think about so he can concentrate more on the terrain.

Where Automatics Are Worse:

Low power rigs where an automatic soaks up too much of that meager power.

Source: Off-Road Adventures Mag Feb. 2006

Tires: Larger tires give your more clearance for obstacles, but usually require a suspension lift (see below) for proper clearance. Mud-terrain tires with larger lugs and bigger gaps between them are the preferred tread pattern for off-road but all-terrain tires which are better on the road are used by many.

Stock Tires are 28-31" (Sport has 29", Sahara & Unlimited has 30" and Rubicon 31". Optional 30" tires avail. on Sport). Each inch in diameter gives you 1/2 in. lift. E.g. 33" tires give 2" of extra clearance on the differential over a 29".
Del Albright says "To many folks, 33 inch tires are barely adequate. That's what I run and I drag a lot."

Tire diameter is not the only issue - tire width is important to. Wider tires increase footprint which can be important for traction or increased flotation. Wider tires may require wheels with less backspacing (See wheels) to get enough clearance from control arms up front and spring cups in the rear.
I got an OME 2 1/2 lift with 33 x 12.5 tires on factory 8" aluminum rims and it hit the spring cups. The solution is to get wheel spacer to move the wheel out or new wheels with less backspacing.

More at Off Road Tires

Braking Warning: Larger tires, lifts and body armor will increase your stopping distance because:
1. Going from a 31" to 33" tire will reduce your braking force by 6% because of the longer lever arm between the brake and the road [brake diameter (same) : wheel diameter (6% more)] .
2. Going from a 31" to 33" tire will add about 20% to the tire weight (47 to 57 lbs./tire) and 6% to the diameter so the angular momentum will increase about 27%.
3. The extra suspension components to lift the vehicle will increase the vehicle weight also. e.g. (Lift Kit difference [40-60#], Tires [40#], Rocker guards [80#], axel, bumpers, ...). 200 lbs. out 0f 3,200 is another 6%.
4. The additional unsprung weight (tires and axels) can reduce traction due to things like tire hop.
Bottom line is you will end up with more than a 10% increase in braking distance.

See Also: Tires under products
and Air Down under tips for more.

Wheels:

Tire width	Rim width
Tire width	Goodyear	BF G
9.2	6-7	6-7
9.7	6.5-7.5
10.2	6.5-8
10.5 x 15	7-9	7-9
10.5 x16	7-8	7-8
11.5 x 15	8-9.5	8-10
11.2 x 16	7.5-9.0	7.5-9
12.5 x 15	8.5-9.5	8.5-11
12.3 x 16	8-9.5	8-9.5

diameter x rim width

Model	stock	optn	Tire
SE, X	15x7		28"
Sport	15x7	30"	29"
Sahara, Unlimited	15x8		30" *
Rubicon	16x8		31"

Optional Canyon alloy wheels are 15x8 with 5 1/2" backspacing and 3.73 gears.
American Racing Series 62 Wheel 15x7 and 15x8 w/ 3 3/4" backspacing are popular for lifted jeeps.
Many prefer steel wheels because they are more malleable; see below.

See: BF Goodrich Mud-Terrain T/A requirements
* An 8" wide wheel and 12.50" wide tire is a very common setup. The relatively narrow rim (in comparison to tire width) is well protected from damage due to the bulging sidewalls. The downside is that the bulge of the tire also leads to premature wear at the center of the tire unless low tire pressures are maintained.

Sometimes wheels with less backspace are used with 12.5" tires to get enough clearance from control arms up front and spring cups in the rear. This also gives you a wider stance, but may put an additional load on wheel bearings. Standard backspace is 4-5.5"; rims with 2" backspace are available.

but you need to have enough back spacing to get your tires out from your control arms up front and spring cups in the rear.

Larger tires will usually require new wheels (rims). Steel wagon wheels, which are much less expensive (only about $35 each) and much more forgiving than cast aluminum (which go for around $100 per rim). A steel wheel will bend, allowing you to straighten it somewhat with a hammer. A cast aluminum wheel will crack, however, leaving you stranded on the trail. And the wheel cannot be repaired; you will have to replace it. For both strength and lightness, you may want to use a "forged" (vs. "cast") aluminum rim. However, expect to pay in excess of $150 per wheel!

Lifts for Wrangler TJ - For street use †
Lifts (raising the body higher above the axle) provides several advantages:

More ground clearance for your oil pan, transmission and gas tank.
You can use larger tires for better differential clearance
Longer springs for more articulation or travel in the suspension. A more flexible suspension will allow the tires to follow the contours of the trail better.

What	None	Average	Hard Core	Ultimate
Lift TJ	0	2.5-3"	4-4.5"	5-6"
Cost₁	0	$600-880	$1,400- 2,600	2,600- 3,500
Tires	30-31"	32-33"	34-35"	>35"
Cost₁	$500-600	$600-780
Lift JK	0	2-2.5"	3-4"	5-6"
Tires	29-32"	33-35"	35-37"	>37"

32x11.5 are the largest tires that a Jeep Wrangler TJ can fit without a lift installed. For street use only.

Note: Off-road use with things like sway bar disconnects may require more lift.
See below.

See: Jeep Tech: Tires at off-road.com
Lift size vs tire size. at sleeoffroad.com
Tire Size Clearance Guide at californiajeeper.com
Wheels at jeep.us41.org for more on tire size.

† YJ - Max 30" with no lift, 33" questionable with 2.5" lift

1 - Cost is lift kit only. Not installation.
See below for other modifications which may be required (lower gears and drive shaft)

The above table is primarily for street use. If you add sway bar disconnects and adjustable shocks to increase articulation (suspension movement) you may need the next lift step up or have to trim the corners of your fender flares for off-road use.

4 Wheel parts has the following Maximum Tire Size Chart:

Suspension Lift for

Addl. Mod. Tire Size

31 32 33 34 35 36

None 2 4 6

2" body lift 2 4 6

Tire width is also a consideration. With the maximum diameter for a given lift you will be limited in width.

Some Manufactures specs:

Mfg. lift Tire

Teraflex S4T 4" 35"

Teraflex S3T 3" 33"

Rubicon Express (RE) 4.5"
plus 1" body lift 35

Rubicon Express 3" 33x12.5

RE Superflex 2" 31x10.5

Rockcrawler 2.5" 33

Source: What lift fits? at yuccaman.com
See links to other pages on tire sizes below.

Other combinations are possible including:
Combination suspension and body lift (max 2")
- A body lift will not raise the gas tank, engine, transmission and transfer case are connected directly to the frame, so under body clearance will not be as much as with a suspension lift and you will not get the extra off-road performance of increased suspension travel. However, you will have a lower center of gravity as the heavy components (e.g. engine) will be lower.
Differential and tie rod clearance are a function of tire size not body vs suspension lift.

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. 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. Source: jeep.us41.org

Trimming the corners of the fender flares or installing wider fender flares.
Note: Body lifts will also reduce slack in some of the wiring. One person said this could be a potential problem.

Vehicles receiving more than a 2.5 to 3-inch lift will require additional parts, such as a transfer case lowering kit (some people still report getting vibration with the transfer case lowered) or slip-yoke eliminator (SYE) for the stock NP231 transfer case. New CV driveshafts ($150+) are also recommended by many lift manufacturers. Other parts (e.g. rear stabilizer bracket) may have to be moved around.

Note: My auto mechanic says he has picked up many a Jeep which has rolled. Lifting your jeep will make it even more unstable on the highway. The Wranglers have a wider wheelbase than the CJs, so are safer.

Legal Issues:
- Light Height: In most states the distance from the ground to the center of the head and tail lights can be no more than 54 inches for headlights and 60 inches (72 in some states) for taillights.

- In many states the fenders must extend over the tires, although this may not be enforced.

New Jersey Lift Law (NJAC 13:20-37.3)
Under 4 inch lift, no tilt test/susp inspection needed. Total lift includes lift from tires, suspension, and body lift combined.

Front fenders must cover tread. Rear flaps must be in accordance with SAE standard J682. ( I think this means 15 degrees up from back of tire must be covered by mud flap).
PA.C.S. 4533 - Equipment should bar water or other road surface substances thrown from the rear wheels of the vehicle at tangents exceeding 22.5°

Max lift heights
GVWR -4500 lbs 7" over orig veh height.
GVWR 4500-7500 9"

Simple Basic Lift:
2" spring spacers (<$200).
1" body lift for about another $80.

At bmja.org/forum/ a comment says "Rubicon Express (RE) lifts are good but sit higher than advertised. RE 3.5 sits closer to 4.5."
RE says their lifts sit higher initially to compensate for a reduction after springs are settled in (1,000 - 2,000 miles depending on how aggressively you use them). Settling can be 1/2 to 1" (average is 3/4").
Note: The additional weight of a hard top will also reduce the lift height.

Short Arm (see long arm below) lifts (in order of unofficial preference) are available from: BDS, Rubicon Express, Black Diamond.

Larger tires lower your RPM for a given speed to the point that you are severely under-powered. This requires you to modify your gear ratio.
Front and Rear Gears - $300

Increased tire diameter increases the torque loads on the axles, u-joints & drive shafts. For significantly larger tires it is usually necessary to upgrade these components. See axle below.

The lift greater than 3" will increase the angle of the drive shaft. Some of the lift kits include components to lower the transfer case to compensate, but this reduces clearance in the middle. A new rear drive shaft which requires modification of the connection to the differential is sometimes recommended, however this can cause vibration if you do a lot of highway driving because it is difficult to center the new components.

A 4.5" RE lift will put the top of a BestTop soft top a little over 6'-8"; Many garage doors provide only 6'-8" clearance. The hard top is a little lower.

Long Arm kits supply a new upper control arm which is longer and requires the attachment to the frame to be moved back, usually to a beefed up transfer case skid plate. (see more on the Rubicon Express Long Arm below.)
The general consensus is you should seriously consider long arms with lifts 4.5" and above.

Review at rockcrawler.com says:

Short arm lifts increase the control arm angle making the suspension harder to react to bumps and shortening the wheelbase. This causes two things: squirrely handling and tires that are noticeably not centered in the wheel wells at ride height. A disadvantage is that because the control arms are not attached to the transfer case skid plate work on the clutch or transfer case will require more time to remove these arms and support the axles.
Highway driving is free from coil spring cycling. Ever hit a large bump with the 4.5" lift? Some people call the result 'Death Wobble'...and it is not fun.

See Long Arm vs Short Arm discussion at jeepaholics.com.

Long Arm (LA) Lift Kits (in order of unofficial preference) are available from: Clayton ($2,100 - 4") (First to produce LA. requires welding), Rubicon Express ($2,500 - 4.5"), Tera, Full Traction, Fabtec (lack of rear pinion angle adjustment), and skyjacker (PITA to install) .
Skyjacker had a 2 1/2" long arm kit.
Fabtech 6" long arm at 4wheelparts.com
The Nth Degree kit was new and not included in the preferences.

Forum Comments on lifts:

Old Man Emu (OME) 2 1/2 lift with 1" body lift is a good combination for 33" tires.
The best kit for the $ IMHO is the Rubicon Express (RE) stuff if you're looking for the most creative kit, check out the Nth Degree Mobility and the Fabtech stuff. butch6924 at pirate 4x4
Daystar Body lift is best. It actually replaces all of the factory body mounts with 1" taller polyurethane mounts. These are the best lift kits on the market.

Rubicon Express (RE) Kits:
Long Arm (TJLA) ($2,500)

    * Increased wheel travel for better traction off road
    * Minimized axle steer through the suspension cycle
    * Decreased torque roll, providing a safer, more controllable vehicle 
Returns a nearly stock ride to a lifted jeep.
The installation of a slip yoke eliminator (SYE) and CV driveshaft
on the stock NP231 transfer case is required.  A new muffler may be required.


Nth Degree Long Arm ($3,400)
Retains factory bushing at axle ends to deliver best possible
ride and fit stock brackets.
'Dog-Leg' Long Arm Design for better clearance.
Unbelievably low Ride 'Harshness' via GyroJoint™-plus-stockbushing
arm design and good control arm
angles

See Also:
What lift fits? at yuccaman.com -
lift options by wheel size at off-road.com
Jeep Tech: Tires - Lifts and Tire sizes.
Full Traction Lift Review (recommended)
TJ Tech from New England Four Wheelers, Inc
Full Traction problems at Rubicon Outfitter Forums
Tire Size Help at jeepfan.com
Tire/Lift combinations FAQ
Rubicon Express, Rancho Cordova, CA
Nth Degree Mobility Lift Kits, Carson City, NV
Clayton Off Road Manufacturing, Waterbury , CT
BDS suspension Coldwater, MI
Links to Suspension Lift How Tos at jeepsonly.com
4x4xplor.com/mods-TJ.html Excellent write ups on mods for a TJ including how to install a body lift and suspension lifts. Very nice.

Axles:
With a 33-inch tire and lockers, particularly with low gearing, the stock Dana 35 axles will snap. You can add stronger axles, but you still have a Dana 35. A popular swap is the Dana 44 or the Ford 9 inch axle. The Dana 30 up front is usually good up to a 35-inch tire.

Dana 44 axles (heavy duty), 4:56 gears. - $3,800 (front and rear)
(Can use Dana 44's from a wrecked Jeep Wagoneer. New rear on e-bay $800)
May require new wheels because of a 6-lug hub
Dana44's are more prone to vibes after a lift, so you have to be careful to center the ?? where the driveshaft connects to the differential.
see Sams Offroad Equip.

Differential: Locking (or limited slip)
According to Albright
"Without a differential modification, your current rig is really still a two-wheel drive vehicle. By modifying the rear axle, you've grown to 3-wheel drive. And by "locking" both front and read diff's, you've now graduated to a true four wheel drive."

Locking (or limited slip) in rear (ARB is most popular.) $615
See diagram at 4x4abc.com/4WD101/diff.html

Tru-Lok diff has limited slip in rear when not locked. ARB is completely open when not locked.

A response at pirate4x4.com/forum under Daily driver lockers.
Personally, I'm not a fan of ARB lockers and never bought into the 'best of both worlds' thinking. Ideally I want all 4 tires turning on pavement, but no binding in the steering, chirping of tires, or fishtailing in snow. Off road I want all 4 tires turning and retain steering ability. ARB, gives you all 4 tires turning when you need it, but when they are off you have open diffs. How is that the best? All at what I consider too much complexity.

I run Truetracs in both diffs. Not the 'best' as I don't get 100% lockup on the trail but on pavement where my Jeep is most of the time they out perform ARB's hands down. All at lower cost, less complexity, and less thinking about what position the switch is in. I've never hear anyone say they can't engage the Truetrac. And if I had to do it today there is the Electrac which gives you a Truetrac that can be locked electrically. That is the best of both worlds in my mind.

Not really bashing ARB as Lord knows they are effective popular enough.

BTW, as far as traction on the trail people normally assume I am locked. And yes, a limited slip in the front is worthwhile.

Another report on the-jersey-devil.com/bbs:
Why limit yourself with a limited slip like the truetrack? They work pretty well, but the torsion gear design just isnt up to large tires. I think even tractech says the limit is like 32-33" tires for them. Drop a locker in the front, you wont notice it unless the hubs are locked. If your swapping gears then go full detroit, if not then drop in either a lockrite or aussielocker. Heard of alot of problems with the detroit ezlocker when they came out so I wouldnt personally go that route, but the aussies have held up great, and the lockrites are proven. As long as the EB has power steering, you will do fine with a full locker up there.

Another forum reported TrueTracks may not be beefy enough for > 33" tires. See: Tractech (maker of the Detroit Locker and EZ Locker) has been able to develop their own line of torque-sensing limited slips they call the Detroit TrueTrac.

Lockers:
Detroit E-Z Locker - Insertable, utilising existing diff carrier housing, full locker, automatically unlocks when turning, easy installation. Visit www.tractech.com

Detroit Locker - Replaces existing carrier (in most applications), thus much stronger than original carrier, full locker, for heavy duty use-competition, racing etc, automatically unlocks when turning, the ultimate locker! Visit www.tractech.com

Detroit Truetrac - Geared limited slip, requires no special oils or maintenance, performs open until needed, perfect for front diffs where steering control is important. Visit www.tractech.com

Lock-Right Locker - Same as E-Z Locker, for some applications where other lockers aren�t available, or if you prefer Lock-Right. Visit www.powertrax.com

ARB Air Lockers at excellent prices! Visit www.arb.com.au for information.

OX locker - new

Detroit Electrac - Basically the Detroit Truetrac clutchless limited slip diff. with some sort of electronically engaged mechanism that turns it into a spool. So you have a full time limited slip that switches to a spool, you never have to run open, yay! And no cluthes to wear out, no compressed air lines that leak. www.tractech.com

Transfer Case: (T-case)
The transfer case which attaches to the drive shaft behind the transmission and directs power to the front and rear drive shafts. It has two main purposes. 1. Putting the jeep into and out of 4-wheel drive and 2. providing a lower gear ratio for off-road use.
They have a 1:1 gear ratio in high and the low gear varies from 2.74:1 in a stock TJ, 4:1 in a Rubicon up to 6:1 in an atlas II.
The stock transfer case was an NP231. New versions of the NP231 are referred to as NVG231 or NV231 which stands for New Venture Gear.
he NP231 used in the Wranglers have an over all length that is long for a short wheel base vehicle. This can cause driveline vibration and premature u-joint failure especially for a lifted vehicle. There are kits to convert the tail housing to a standard yoke to allow the use of a longer rear drive shaft. There is also a 4:1 low range reduction kit for the NP231.

An Atlas II transfer case has several advantages:

Superior strength
Shorter (6½" shorter than an NV231 without a short-shaft conversion kit) allowing for better drive shaft angle on lifted jeeps
Shift-on-the-fly feature
Low-range ratios of 3.0:1, 3.8:1, 4.3:1, 5:1 or 6:1 are available
Individual axle control with two shift levers so you can have (1) front wheel drive only (2) 2WD low to reduce drivetrain binding when one encounters tight turns on the trail with lockers.

See: Atlas II notes.

WARNING
A higher center of gravity and larger tires affect the handling requiring safe driving techniques. The higher center of gravity increases the chance of rollover and loss of control. Larger tires with greater rotational momentum and the extra weight of lift and armor components will increase your breaking distance.

See: Center of Gravity and Roll-Over Angle - Jeepaholics Anonymous

Required

Towhooks (front/rear)

See CheckList.
Optional/Recommended:
See discussion below.

Winch (A Hi-lift Jack or come-along and tow strap is a poor mans alternative)
Rack (assuming you want to leave back seat in for relatives, dogs, or relatives who are dogs)
Skid Plates:
Skid plates covering the gas tank and transmission/transfer case are recommended for all trails rated 4 and above per Jeep Jamboree USA.
- Rocker Panel Guards (Rock Sliders) ($250-300)
  Nerf Bars ($140)
- Gas tank skid plate. You can get one that goes over the stock skit plates on Wranglers to provide better protection around the edges.
- Engine/Oil Pan Skid plate - $125
- Belly UP Skid plate ($325) can add 2" of clearance at the transmission and transfer case, but can make the driveshaft angles severe. This requires fine tuning to eliminate drive shaft vibration.
- Differential Guard (Most people do not use because it reduces clearance. You can avoid differential damage with driving techniques, such as planting your tires on obstacles. However, this technique does make it more important to protect your rocker panels.
Stronger Bumper ($200 each/front & rear); may include stronger spare tire carrier for larger tires and space for HiLift jack ($500). A Receiver Hitch may be included in bumper, but most of these (e.g. Warn) are not rated for towing. In fact their receiver is slightly smaller than 2" so standard balls won't fit.
They are used for accessories such as tow hooks, bike racks, storage racks, ... Most accessories require a 2" receiver although the smaller ones are getting more popular.
See hitches below.

Sway Bar Disconnect:
To achieve maximum articulation (about 4" more), for rock crawling only, disconnect the front sway bar end links. [Disconnect kit ($90)] DO NOT OPERATE THIS VEHICLE ON PUBLIC ROADS OR AT SPEEDS GREATER THAN 15 MPH WITH THE SWAY BAR END LINKS DISCONNECTED.
DISCONNECTING SWAY BARS MAY INCREASE YOUR LIKLEYHOOD OF ROLLOVER OFF-ROAD ALSO.
Note: When the front wheel goes over an obstacle, disconnected sway bars allow more articulation and have a leveling effect. When the back wheels go over an obstacle or you are on the side of a steep hill (try to avoid this) disconnected sway bars will allow more body lean increasing the chance of a rollover.

(See JKS Quicker Disconnects also).
Note: Disconnecting the sway bar will make your vehicle more prone to roll over. 2007 jeeps have an electric disconnect switch, so you can disconnect or connect depending on the terrain.

Bottom Line:
According to Foothill Off-road Products a 4.5" lift, 33" tires, heavy duty drive train, locking differential, etc. would run about $6,500 installed.

Examples:
Empty Pockets Budget buildup
Glen's Jeep

Engine Modifications:
With larger tires and extra weight of optional equipment you may want to modify your engine to increase horsepower. Some modifications are:

Air Intake Systems (May improve mileage also)
AEM Brute Force (article at 4wheel drive mag.), True Flow, K&N, AIRAID, AFE
See Air Filters in Products.
Throttle Body Spacers are also supposed to increase performance, but a 2005 article at SUV World says:
The original idea of adding some space between the intake manifold and, back then, the carburetor was to improve the downward curve of the air and fuel so that it does not hit the bottom of the intake before it is directed into the intake ports. This is not the case with fuel injected engines. It would appear that the spiraling effect would have to carry all the way through the intake manifold and end up in the combustion chamber. ...
They concede there may be other effects which lead to some higher rpm power, but say further investigation is required.
Exhaust manifold
ECM (Engine COmputer) modifications.

Onboard items
First Aid Kit, Fire Extinguisher, Recovery Strap
Hi-Lift jack ($50), Compressor or tank for airing up tires. (see trip list)

Tools:

1/2" Drive Ratchet and Sockets (metric and imperial sizes)
Open end and box wrenches (metric and imperial sizes)
Torque Wrench (250 FT-LB capacity)
Allen keys
Torx bits
Circlip pliers

See Trip Checklist
and bolts (sizes, grade, class).

Tops, Doors, Fender Flares:
Soft top $520-$1,100
Inexpensive after market tops don't always fit right.
Besttop - Supertop w/ 2PC door $785 (at Quadratec)
SunRider $700 + 2PC door $500 = $1,200 (at Quadratec)
Bikini top: $55-100 + Windjammer $70-$85
Molded (Hard) Bikini: $400
Doors: Fabric - $180 pr.; Alum - $300 pr.
Cover: Cab cover $40 Quadratec, Trail Cover $110 BestTop (seem to be same thing)

Fender Flares: $250-500 ($350 w/ rocker extension) (set of 4)

Bushwacker
Poc keet Style 6" $500
Flat Top 7"
Warn 6 or 7" $425
BestTop $315
Omix-Ada (Crown) 7" $150 sold by RuggedRidgeOffroad.com and Outland Automotive. JeepForum reviews say they look a little funny but are rugged can be pushed back out after hitting something with no damage.
Outlander

BestTop
www.4softtops.com/
jeepworld.com/accessories/wrangler/softtop.htm
See Dealers and Mail order web sites below.

Other Accessories:
Batteries
Some people like sealed batteries (Absorbed Glass Mat (AGM) or Gell Cells) because the electrolite (sulfuric acid) will not splash out.

For winching, you want a starting battery, not a deep cycle.
Because starting batteries are designed to flow a lot of current, accept higher charge rates (faster to recharge) and are a lot less picky about how they are charged (temp compensation etc). This makes them perfectly suited for electric winches which demand an unholy amount of current (upwards of 400 amps), and if you discharge your batteries during a long winching bout, you want to recharge them as quick as you can to unstick yourself.

See Batteries in Home and Garden, Auto and Products.

Tailer Hitches
A receiver hitch (square tube which accepts interchangeable hitches or other accessories) is preferred because you can get inserts with drop downs for different ball heights to match the trailer tongue and use other accessories designed to fit in the receiver.

Hitches which mount under the bumper (e.g. Hidden Hitch) are usually stronger but reduce the departure angle. Receivers built into the bumper are generally weaker and not rated for towing.
Although the Jeep is only rated for a 2000 lb. tailor (Class I), most people get a Class III hitch to get a 2" receiver which accepts more accessories (carriers, tow hooks, ...) than the 1 1/4" receiver.
Most boat trailer now come with surge brakes, which theoretically would allow a heavier tailor.
See: Towing at the Jeep page and "Products > Hitches"

Some people replace the carpet with Spray on Rhino lining.

Storage:
Tuffy - Trunk & Rear Storage
Tuffy Expandable Rear Security Lockbox $410
Security Lockbox $443
BestTop ExtendaTrunk $200, Besttop modular system
WildernessRacks.com
Security: Locks (Door, hood,)
Tuffy
hood locks

Radios See:
Communications from the Rubicon and the Tahoe Area for information on ham radio.
Personal radios at Products
Installation of radios at hobbies
Amateur radios at hobbies

Others See Trip Checklist.

Tips & Maintenance notes

Light switch with door removal:
How do you get the interior lights to stay off after you remove the doors?
Remove the "Door Switch Defeat" fuse (#4 - A 10 Amp [red] fuse.); It's designed for this purpose, so you can still twist the light switch to turn on the light after removing the fuse. Fuses are in the box behind the glove box (Take the strap off the glove box and tilt it all the way down to remove). (Note: TJs have another fuse box under the hood on the right hand side. Fuse #17 in this box does the same thing). The headlight warning alarm, when you take the keys out with the headlights on, and possibly the dash lights are also on this same circuit.
(On YJ's it is called "Door Jam Defeat")
Check Engine Light: On a 1997 TJ you can get the Diagnostic Trouble Code (DTC) without taking your jeep to a dealer or service center with a computer. Turn the ignition key to the "On" position three times in succession (i.e., On, Off, On, Off, On).
Malfunction Indicator (MIL) (Check Engine) Lamp will flash the appropriate number of times to indicate the Diagnostic Trouble Code (DTC). 2 flashes followed by 5 indicated code 25. The DTC will also be displayed in the odometer window.
1998 and newer models will require going to a dealer or getting a Diagnostic Code Reader or OBD-II Scanner
See Check Engine Light
Chrysler parts departments have a plastic window cleaner/polish that will help the cloudy windows a lot.
Bad Mileage - Have a dealer run the MDS (Mopar Diagnostic System) analyzer on it.

See troubleshooting.

Other Information

crawl Ratio - Forces - Stress (Do the math):
Terms:
GVW - Gross Vehicle Weight (Incl. passengers and cargo)
Crawl Ratio - The maximum multiplied lowest gear ratio. First gear, transfer case low range, and axle (differential) ratio.
For a TJ In 1st Gear w/ Automatic: 2.74:1 (Manual 5-spd 3.83:1); Transfer case Low Range: 2.72:1; Differential: (Dana 44 - 3.92) Transfer Case - The gears which transfer power to the front wheels and usually have a low and high range in 4WD.
Gear Ratios:
Crawl ratios in the 60's are quite capable; in the 80's, very respectable, in the 110's, impressive and anything beyond the 130's is usually considered the point of diminishing returns.

'97 Wrangler 4.0-L 6 cyl in 4WD Low Range <

5 spd Manual 3 spd Auto 4 spd Auto Rubicon

manual auto

Transmission
1st gear 3.83:1 * 2.74:1 2.84:1

Transfer Case
low 2.72:1 2.72:1 2.72:1 4:1 4:1

Differential 3.07 † 3.07 3.73

Dana 44-3 axle 3.55:1 3.55:1 3.55:1 4.11 4.11

Crawl Ratio 32
41 w/ 3.73 23 65 41

* NV3550 5 speed overdrive on later model X, Sport, Sahara & Rubicon is 4.04:1
† Optional 3.73
Weight: 3,229 lbs, + Gas 19 gal. @ 5.6 pounds per gal. = 106 , people 350, gear 100 = Total 3,785 pounds.
Transfer Case rations are usually 1:1 in Hi
Common differential ratios are: 3.07, 3.55, 3.73, 4.10, 4.56, 4.88, 5.38, 6.17. See Gear Ratio Guide for Larger Tires at the tires page.
Rock-Trac is the transfer case on Rubicons

Transmission ratios:

1st 2nd 3rd 4th 5th Rev

AX-15 3.83 2.33 1.44 1.00 0.79 4.22

AX-5 3.93 2.33 1.45 1.00 0.85 4.74

30/32RH 2.74 1.54 1.00 2.20

4 speed Auto
unlimited 2.84 1.57 1.00 0.69

AX-15: The AX-15 is a medium duty 5 speed manual transmission. It was introduced in mid 1989 with the 4.2L engine. The AX-15 is still used in TJs and XJs with the 4.0L engine.
AX-5: The AX-5 is a light duty 5 speed manual transmission. After mid 1989, the AX-5 has only been used in 4 cylinder Wranglers (YJs and TJs), Cherokees (XJ).
30RH - 3 speed automatic used with 2.5L engine
32RH - 3 speed automatic used with 4L engine

See:
Gear Ratio Guide for Larger Tires at the tires page.
Common Transmission and Transfer Case Ratios at: 4lo.com
Jeep Transmissions at jeeptech.com
gear ratios and crawl ratio explained at 4x4abc.com

Engine Power:

Other
Web Pages on Modifications:

Del Albright's Rubicon Trail Mods
YJ Transformation, From Mild to Wild in a Month 
How to purchase the best jeep lift kits with Tech. Tips.
Pirate4x4.com - Forum, Product Reviews, Tech Articles, Trail Reports
Quadratec.com - Accessories
Rubicon Express - Manufacturer in Rancho Cordova, CA.
Foothill Offroad Products in Auburn, CA
Oasis Off-Road Manufacturing
Why Modify your Jeep - Article at From the Louisiana 4x4 Club.
Jeep Tech Electrical 
Stu Olson's Jeep Site

Tech Corner at OffRoaders.com
Trial & Error - Product Reviews and Tips at DirtRoadMagazine.com
rockcrawler.com/techreport
jeepaholics.com
yuccaman.com/jeep/
4x4xplor.com
Tech Reports and Reviews at RockCrawler.com
4 Wheel Drive 101 by Harald Pietschmann
Jeeps Unlimited Tech Tips

Essential TJ Mods - Before you hit the rocks! at off-road.com

Equipping your rig

Jerry Bransford's Geezer Jeep Site

Books:

Factory "Service Manual" $90 - Chrysler Service Publications 1-800-890-4038
View Manuals online at techauthority.daimlerchrysler.com for $20/24 hrs.
In "Jeep Owners Bible" (below), Ludel says "The factory manual provides the most information, greatest detail and best illustrations.
"MOTORS Truck Manual", and Mitchell service books have service information for older Jeeps.
"Jeep Owners Bible" (Description at 4x4books.com), 2003, Moses Ludel
4 Wheelers Bible
Jeep 4x4 Performance Handbook, 2007 revision by Jim Allen "Jeep 4x4 Performance Handbook"
How to Modify Your Jeep Chassis and Suspension for Offroad Use by by Jp Magazine