The Jeep Geek

The Jeep Geek's Blog
Sep 2010

A Few Notes on Tires

The Jeep Geek has a new favorite tire. Over the years he has gone back and forth between BF Goodrich and Goodyears. However the new Goodyear Wrangler Kevlar has captured his cold hard heart.

One wonders if The Jeep Geek will have enough to say on the subject of tires to fill a blog article...doubtful, but he can be surprisingly pedantic and verbose.

We digress, tires make the world go round. Well maybe they don’t, but tires are an often overlooked consideration when contemplating modifications that will perform both on and off-road. The quality of tires will either provide the traction needed to gain full enjoyment out of your 4 wheel drive system, or slip and slide on both the rocks and snow covered roads. The Jeep Geek is often surprised to see someone spend thousands of dollars on lifts, bumpers, body armor, winches, compressors, engine modifications and then purchase awful tires that don’t perform well and make a ton of howling noise on the highway.

So the primary job of the tire is to transfer the torque of the drive line to the ground via traction. Traction is measured on various surfaces. A tire that works well on dry pavement may not provide much traction on a slippery rock, or snow. Designing a tire that performs well on all surfaces is extremely difficult...if not impossible. Design trade-offs have to be made to provide a tire that excels on a particular surface. They will not perform as well on other surfaces. So the trick is finding something that is balanced for a number of surfaces.

Off-road tires have, historically, had two annoying characteristics: They tended to be noisy on the highways, and the tread life was low. Improvements have been made. While there are still in-expensive off road tires out there with these same short-comings, the BF Goodrich Mud Terrain T/As and the Goodyear Wrangler Kevlars are notable exceptions.

Both of these tires use a variable spacing on the tread to reduce highway noise. This makes for a much more pleasant highway driving experience...much quieter than other off-road tires. They also have great off-road traction as well as good traction on roads. The Goodyear tire also has very good traction in snow which makes this an ideal tire for our conditions here in Colorado.

As far as tread life is concerned, the BF Goodrich tire is rated at 40,000 miles (The Jeep Geek’s experience is that the BF Goodrich gets just under this lifespan). The Goodyear tire really excels here. It is rated at 60,000 miles. This additional lifespan makes the premium paid for the tire a more cost effective choice.

One further advantage of the Goodyear tire is the quality of the construction of the bead. The tire bead is so well formed that for tackling slippery rock, the tire can be aired down to 8 lbs. This increases the surface patch. This larger surface patch allows for more traction. In fact the tread of the tire extends pretty far down the sidewall of this tire. The BF Goodrich tire can also be aired down to about 15 lbs allowing for a large surface patch as well, but smaller than the Goodyear.

One final advantage for the Goodyear tire is that it uses Kevlar belts which makes it much harder to puncture that other
blogEntryTopper fabric or steel belts. All-n-all this Goodyear tire is a great tire and is the recommended tire for all of The Jeep Geeks friends.
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The 4 1/2 Inch Lift

The Jeep Geek has been promising this article for quite a while and he hopes that the article meets with the enhanced expectations due to the delay. It has been a very busy time for The Jeep Geek as Jeep sales are up quite a bit over last summer and things certainly look like we have turned the corner economically here in the Front Range of Colorado. Not everyone who wants a job has one yet, but things seem to be getting better every month...or maybe we are learning to settle for less...The Jeep Geek doesn’t know which, but he has time this morning to write this.

The higher the lift, the more complex the engineering issues become. This is because the geometry of the suspension changes, and with larger tires, the forces on the drive line increase. These changes and increased forces have to be dealt with or damage to the drive line becomes more likely. In fact, some significant safety issues can be injected into a poorly designed lift.

So the first issue, short-arm or long-arm lift? The Jeep Geek recommends long-arm lifts if you are going to lift more than 2 inches.


Pasted Graphic 1

Short Arm show above. This lower arm is located here from the factory. If the suspension is lifted more than a couple of inches (say 2), the mounting point remains the same and the angle becomes more obtuse and is not able to withstand the forces that will be encountered off-road.

Now for the Long arm:


Pasted Graphic 2

Notice that the lower arm is much longer, in fact in this picture you can see the original mounting bracket and the long arm attached quite a distance beyond this. This geometry allows for a more robust connection to the frame and makes it possible to withstand greater forces on the wheel. From the two pictures, you can see that the material is also more solid for the long arm, further strengthening the suspension.

Another consideration in these more extreme lifts is drive shaft angle. It is not possible to re-use the factory drive shafts with this much lift as the angles will be greater than the 10 degree maximum for a universal joint. The replacement drive shafts used in the Mopar 4 1/2” lift kit are heavy duty and have double cardon joints. The heavy duty part is a result of the added drive line pressure from moving larger diameter tires. In fact up to 20% more force on the drive shaft from the larger tires. The double Cardon joints are composed of two U-joints which effectively doubles the amount of angular change.

For those who purchase a third party lift kit, buy the upgraded drive shafts otherwise you will be presented with a recovery event when your drive shaft breaks at the U-joint. With 20% more force on the factory drive shaft, coupled with a more severe angle than the U-joint is designed for, there will certainly be a failure...probably on a trail where AAA will be hard to contact.

So a word about shock absorbers. Most third party kits don’t include these...don’t skimp here. With the more extreme lifts like the 4 1/2” lift, making them perform on the highway safely becomes more difficult...especially tuning them with the Electronic Stability Program which rides on the ABS. It becomes harder to make all this work with cheap shocks whose characteristics are radically different from the OEM ones, and cheap shocks change their damping characteristics more quickly than better shocks. What this means is that cheap shocks that worked right after installation, don’t 5000 miles down the road.

In general The Jeep Geek likes the Mopar 4 1/2” lift kit because all of these issues have been addressed (together with half a dozen other issues that The Jeep Geek will discuss another day). While the cost of the Mopar Kit is higher than other third party kits, if you add the missing components to the third party kits, the cost is very close to the Mopar kit.

A couple of last minute considerations. Just like with the 2 inch lifts, The body pinch weld needs to be clipped near the rear tires. Also, the stock OEM bumpers will rub a 37” tire when they articulate up, so when installing the lift kit, it is time to replace that bumper.

Also, the stock OEM wheels will not work with the 4 1/2” lift kit. you will need wheels with a 4” positive offset to clear the frame members once the lift kit has been installed.

As long as you are doing all this, might as well put an off-road front bumper (with a winch) on your wrangler. All in, you are looking at about $15,000 to perform all the modifications assuming you use a shop to install these items.

Here’s the complete list of stuff:

  • 4 1/2” long Arm Lift Kit Including shocks, drive shafts, shimmy shock - $5700

  • 5 wheels and tires - $2500 (including the tire pressure monitors)

  • Rear off-road bumper - $750

  • Tire Carrier for rear bumper - $750

  • Front bumper and winch - $2500 (can be a little less, but budget for a good one)

  • Flat top off-road fenders - $1200 Gives a bit more room for full articulation

  • Labor to install all the stuff - $2500 (This will take a good technician 4 to 5 days to get it all done correctly)
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Winching

A winch is a handy device to add to your Jeep. It is useful in a number of circumstances that you will face on the trail. The Jeep Geek has mentioned that it is useful when fording a stream, but this picture (above) shows another application.

Here the driver has determined that the trail is too slippery to drive. The ice on the trail may cause the Jeep to skid off the trail and careen down the hill. A carefully located tree strap and the winch line are placed on the high side of the trail. The driver then carefully draws the Jeep forward with the winch and if there is any slippage then the winch line keeps the Jeep on the trail.

So a winch is useful when there just isn’t enough traction to overcome an obstacle. Other circumstances include steep grades, boulders, muddy trail, sand, and as mentioned...ice on the trail. It is also useful when the Jeep is stuck...self recovery...Or when the Jeeper encounters another vehicle that is stuck (probably not another jeep).

The Jeep Geek has seen several cases where an off-roader has broken an axle because the driver didn’t winch over an obstacle. They instead rocked the vehicle back and forth by shifting the transmission between 1st gear and reverse. This maneuver places strain on not only the axles, but the entire drive line...it is possible to blow out a U-joint or damage the clutch. These hapless drivers find that a winch is about the same cost as replacing an axle or drive shaft, and then the next time they have more off-road capability with a winch. These drivers feel especially dumb when they already have a winch installed and didn’t use it.

So what type of winch is needed? What size? Where should it be mounted?

Well The Jeep Geek recommends at least a 9500lbs winch (even though the Wrangler is only about 4000lbs. The reason for this is the rating of the winch is measured directly at the bottom of the spool. Each wrap of the winch line derates the pulling capacity...if you have 4 wraps of line on the spool, the spool diameter is greater and the pulling capacity is only about 6500lbs. It is best to have a bit of over-capacity when winching so a rule of thumb is to ensure that the weight of the vehicle represents 60% of the winch capacity. This prevents burning out the winch and also have the capacity to over come drag (from the frame dragging along rocks) and suction (that may be present in mud).

The most common type of winch available today is an electric winch that runs on 12V electric power of the Jeep. There are some power-takeoff types still out there, these run on a pulley that is driven by the engine, but these are rare and not really as useful as an electric winch since the engine must be running to operate the winch.

As far as where to mount the winch, most are mounted on the front bumper, however The Jeep Geek has seen some that are mounted on a trailer tow receiver hitch that can be mounted on both the front and rear bumper. The rationale for this approach is that sometimes the Jeep is facing the wrong direction to permit effective winching in a recovery mode. While this is certainly an inventive approach, there are other techniques that permit winching out of such a situation. With the hitch receiver mounted winch, the user should be aware that a winch is very heavy and it is nontrivial to haul this winch to the other side of the Jeep and mount it for action.

So a word on the bumper is needed here. There is no place to mount a winch on the factory bumper of a JK vintage Jeep, so an off-road bumper with winch mounting plate is needed. Older Wranglers have steel bumpers that can support a winch. Regardless of the vintage of Jeep it is vital that the winch be mounted on a surface that is securely attached to the frame of the Jeep otherwise damage to the bumper or body of the Jeep is possible (read probable).

Now safety is an important topic to cover in winching. If the winch has steel cable installed on the spool, you should be aware that force is loaded on steel cable. What this means is that the steel cable holds this force and if the cable breaks it will whip back with extreme speed and force. This can cause severe injury if someone is hit by the cable. The Jeep itself can also be damaged if the cable hits it. It is always a good idea to place something over the cable such as a heavy blanket or coat over the winch line to dampen the force in the event of breakage. Also, the winch line should be periodically inspected for rust which will weaken the line.

Most winches have a remote control unit that permits the operator to stand away from the winch to prevent injury if the line should break. Keep your eyes and ears open when winching so you will know if and when the cable breaks.

The Jeep Geek recommends that the steel cable be replaced with synthetic line. There are a couple of advantages for this. First, synthetic line does not load like steel cable. This means that if a synthetic like breaks it will just drop harmlessly without whipping back at the operator. Also it is lighter than steel cable and the lighter you make your bumper, the more clearance in the front you will enjoy.

Another safety consideration is to always wear heavy leather work gloves when working with the winch line as individual strands of the cable can break and cut your hands. Always keep a pair of gloves in your winch accessory kit.

On the subject of an accessory kit...there are a few items you should carry in your Jeep if you have a winch. You should have a tree strap so that you can attach to a tree as an anchor point without damaging the tree. (Never loop the winch line around an object and place the hook on the winch line. This will damage the line by placing severe force on a small portion of the line.) You should also have a recovery strap that can be placed on one of the tow hooks of the Jeep for pulling another vehicle out of trouble. A recovery strap is a long length of fabric or synthetic material that does not load like steel cable. Also a snatch block should be part of your kit. A snatch block is basically a pulley that can double the capacity of your winch and is useful for recovering a vehicle that is heavier than your Jeep (such as a pickup truck). It is also useful for maintaining direction if your recovery requires you to make a sharp turn in direction during the recovery.

As you can see, having a winch will enable you to traverse terrain that might not be possible without some assistance. This will allow you to go further down the trail and discover something that others will miss due to a lack of equipment or tech
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All 2 inch lifts are not equal

So in the last post we discussed clearance issues to determine how much lift is needed. In this issue we will focus on 2 inch lifts and discuss the various considerations in picking a particular lift. The Jeep Geek will also explain why he feels that the Mopar 2 inch lift is ideal for most cases.

The Jeep Geek knows of lift kits that cost under $400 that include 4 2” spacers and four shock absorbers. The idea is to leave all the stock components in place (except for the shock absorbers) and place the spacers on the top of the coil spring to extend it’s size. These will give 2 inches of lift and permit the installation of larger tires, but there is a problem.

These kits are dangerous. They limit articulation so they are not good for off-road. (In fact they can articulate down and rip out the brake line...but cannot articulate up.) In addition they are not safe for on-road use as they change the suspension geometry and leave the vehicle subject to severe vibrations (sometimes called death wobble). If you cannot afford a correctly engineered and installed lift kit...wait...don’t install a cheap one or it will cost you much more in the long run.

So briefly lets look at a budget to do a lift. There is the cost of the lift kit, new tires, new wheels (yes the stock wheels will not work as you will need wheels that are offset to allow the larger (and wider) tires to clear the body, a rear bumper with tire carrier (you can’t mount the larger wheels and tires on the stock tire carrier). A reasonable budget will break down similar to:

$1600 for the lift kit
$3500 for 5 new wheels and tires (could be as low as $2500 for really cheap tires)
$1500 for rear off-road bumper with tire carrier
and about $1000 - $1500 for installation labor. Yup, there is a lot of work involved to get all this installed correctly.

So, how smart did it seem to put a $400 lift kit on in light of the other expenses. Bottom line is a $400 lift kit is unsafe at any speed.

At a minimum the lift kit you choose should include 4 heavy duty longer coil springs. 4 high quality shock absorbers, steering linkage to maintain steering geometry, anti-sway bar extenders, new bump stops to prevent over-articulation, an oversized steering stabilizer, and either new brake lines or a kit to move the brake line links to allow for articulation.

So why heavy duty coil springs? The Jeep Geek is glad you asked. You jeepers insist on bolting things like off-road bumpers, winches, gas cans, cargo baskets, etc to the bumpers. These add weight and have to be compensated for with heavy duty springs.

So lets assume that you have all these parts, are you good-to-go?
Not necessarily. Do the parts work together, are they engineered as a unit? Are they tuned for highway speeds, cornering, to work with the Electronic Stability Program of the Wrangler? If not, then there may be drivability issues. This is why The Jeep Geek likes the Mopar engineered solution. It was designed to work with these systems in the Wrangler.

As you can clearly see in the picture above, the lift includes a heavy duty steering stabilizer. Without this, any lift could be prone to high speed instability. A number of Jeep forums have documented this “Death Wobble”. In all the examples that The Jeep Geek has seen, this occurs on poorly lifted Wrangler JKs. If your lift doesn’t include an upgraded steering stabilizer you are asking for trouble down the road.

Now it is important to discuss some installation issues. First, the Mopar kit allows for full wheel articulation. This may require some modification to the body and fenders if 35” tires are mounted. The pinch welds of the body pans near the rear wheel will have to be trimmed slightly (just about an inch of the corner). If the factory rock rails are installed, they will also need to be trimmed slightly as well (to match the body trim).

Second, the rear fender may have to be replaced with a high clearance fender to allow 35” by 12” tires to fully articulate up. The Jeep Geek has seen some fender rubbing with the factory fenders. Mopar has released some flat fender flares that handle this issue nicely as well as provide a handsome and muscular appearance. These can be purchased for about $950 for all 4 fenders. The Jeep Geek will post some pictures of this shortly.

Now you are ready to do some serious rock crawling. Have fun out there.
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Stiffer is Better

So The Jeep Geek promised another article on lifting Wranglers, but he is sidestepping a bit with this article. This article is regarding the new 2011 Jeep Grand Cherokee. This is not going to be the typical fluff piece that The Jeep Geek has been reading all over the internet...it is pointed at the totally lame marketing he sees at Jeep HQ in Chrysler. He does have hope as there are a series of commercials that are about to debut this month that make The Jeep Geek’s heart beat faster.

The subject of stiffness will apply to lifts and The Jeep Geek will develop this thought regarding lifts later this week.

The concern centers around a commercial that has been running that shows a bunch of robots welding a Grand Cherokee frame. The announcer says something like “why do we use 5400 welds on the new Grand Cherokee? Because we aren’t just building a new car, we are building a new company.”

What??? The Jeep Geek has a marketing background and has seen slick ad agencies pitch slick ad concepts that do nothing to promote either the brand or communicate the central value proposition of the product. The ad in questions falls into that category.

Here is why The Jeep Geek cares about 5400 welds (and why you should as well). The new Grand Cherokee has a body that is 146% stiffer than the previous body. Now the previous body was pretty good as far as stiffness is concerned. Some of the reason why the new Grand Cherokee has a stiffer body is the number of welds.

So why do you care about body stiffness? The Jeep Geek is glad you asked. There are several benefits of a stiffer body. First, the new Jeep Grand Cherokee handles better in high speed corners. This is because when a vehicle turns at high speed there are forces exerted on the body and it flexes a bit. When the body flexes this change in shape often changes the steering geometry. Not a big deal in slower turns, but becomes a big deal in high speed turns. The Jeep Geek can tell you that he has personally taken the 2011 Grand Cherokee on test drives with high speed turns and it holds the line beautifully. Better than anything in its class.

Second, a stiffer body yields a quieter cabin. The 2011 Grand Cherokee has a quieter cabin than most of its competition...The Jeep Geek has seen this personally as he has driven these competitors against the Grand Cherokee in a number of situations.

Third, the stiffer body allows for the doors to be opened when the Grand Cherokee is rock crawling with opposing wheels fully articulated. Not all competitors can say that. It isn’t a good thing to be stuck on rocks and not be able to get out of the vehicle because the body has flexed so much that the doors are jammed.

“So why do we use 5400 welds in the new Grand Cherokee? Because we are intent on building the highest quality, best performing vehicle in its class.”
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