As we move to larger and larger tire sizes we inherently alter the caster due to the larger tires footprint. Large tires give you more positive caster. To compensate, we need a new caster setting to offset the larger tires. Tire diameters will depend on air pressure and actual specs for the brand and model of tire.

You might note that I ran 18 lbs of air pressure, OEM called for 34 lbs IIRC. So how did I arrive at that figure?

Tire Contact Patch or the footprint. Several ways you can do this.

Find a empty parking lot a day or two after a rain, find a wet spot large enough to get both tires on each side wet the drive forward and back to see the footprint. Air down until you get an edge to edge and good tread definition. Since I run OBA (on board air, Warn Powerplant) I would adjust my TP up/down until I got the foot print I wanted. At 34 lbs and the weight of my Jeep about 4800 lbs (OEM was about 3400), 34 lbs did not allow a full contact patch for street/highway driving. Off road I ran 3 lbs.

NOTE: Big (Tall) tires mounted on small diameter wheels can induce DW at low air pressure, this is due to the sidewall flex which also allows lateral movement or what is uncontrolled 'reciprocal oscillation'.

 

hey 17 Oaks... Thanks for the correction. I am aware this can happen on anything with front wheels. I've had my share and I should have been more clear in saying that in most cases control arm suspension (independent) is less apt to get the wobble vs solid axle type. Good write up on what to check. Most frustrating is what may fix one may not fix another.

 

Fortunately for Superduty owners, our trucks have a long wheel base and are more inherently stable. Also they are heavy with unsprung mass low in comparison. The 66-77 bronco's have the same suspension design, and many suffer DW and poor handling as they are old (worn out bushing), short wheel base, narrow, and lifted high on big balloon tires. My old bronco drove beautifully on 37s at 25 psi, even at 80mph, with soft springs no sway bar. why? I added 8 degrees of caster for a 4" lift where only 4 is need to 'get back to stock'.


No need for Band-Aids like dual stabilizers. Fix the root of the issue

 

I strongly believe that if you want to fix DW then you either must understand it or know someone who does, I can fix it because I understand it.

When I did my Rubicon build back in '03 I spent 3 weeks building it, but as I got down to the very end in the tuning phase I did not have a Steering stabilizer mounted on it., spent a lot of time tuning and got lulled into thinking I could get by w/out a SS. I was running some SERIOUS axles: Dynatrac ProRock HiPinion, 35 spline ChroMo shafts, ARB locker, Front High Steer, front and rear D 60's. Life was good for about a year + then one day I got DW on the way to the Off Road Show out in Pomona Ca in I 10 traffic just outside of LA...band news. I left for home Monday and found a sweet spot the Jeep would work at sans DW.

For the next few weeks I spent at shop after shop after shop with some of the so called experts in the Jeep scene. I heard every fix and cure you can imagine. All the while my DW getting worse, finally to the point it was undrivable at any speed. After spending far more money then I should have with near ZERO results and the tow bills mounting up due to not being able to drive it at any speed without DW. I finally slapped myself up side the head and said Don, you are an engineer, retired, but and engineer still and its up to me to fix it.

This became and odyssey that lasted about 6 mo's and took me to shops and discussions with folks across the spectrum to include a half day coffee fest with 2 Chrysler Jeep Engineers.






This is the culprit, a track bar with a vertical frame side attachment, its the same setup as used on the tie rod and yes it does the same thing as it wears, it moves laterally.





This is how I solved the problem. I designed my own track bar. On the right is the frame side, using a mega Johnny Joint I gut from Currie Enterprises, the tube and left bushing I got from JKS. Tube is ChroMo .120 wall 1.25 in diameter.





Here is the new frame side track bar mount, braced and boxed. I was able to shift it enough to run a straight TB instead of the OEM curved unit.





Johnny Joint welded and STRAPPED! The JJ fits in side and give a HORIZONTAL 2 point support (double shear) using a Grade 8 bolt. DW generally has its origins in the TB, because that is what locates the axle laterally and it takes all the weight...my D 60 front axle weighed in at about 700 lbs complete with 37" BFG KM2 on Walker Evans Beadlock wheels

If you can get the axle solidly mounted under the frame as I did, then after that is a matter of maintenance in your components such as tie rod ends, bushing, SS, shocks, proper alignment specs for YOUR unique setup, tire pressure and ball joints. Solve the Track Bar problem and you are well on your way to a home run...





Compare this setup to the OEM tie rod end bent like a snake track bar.

 

Nice work. Those are some sweet axle$$$. Engineers can figure out anything (except women) or so we think! What type of engineering did you do? I'm an EE.

 

Thank you

EE, I take my hat off to...YOU are the smart one, you can do math, I can only work with 1's and 0's. Software, Hardware and Network Engineer. Early days I was a Mech Engineer then I decided to change fields or rather it was decided for me by the Army...new field and they were looking for bodies. I was at 10 year point in my career as an Infantry soldier. I agreed to take one tour and then back to Infantry. About halfway into it, dead of winter I realized that for the FIRST time in my military career I was not HOT, HORNY or HUNGRY and spent the next 25 years in IT...R&D for the first half of that like being in heaven...

 

On all my mud trucks and my FJ40 with 37's I have added 2-3 degrees of positive caster when moving to the larger rubber.
Although I have no death wobble in any of my SD's the first thing I would do would be caster correction if I had a new truck that had this problem.

 

Fellas,

I have a 2015 F250 Xlt with 285/75/17 AT2 LRE tires with -12 offset wheels. The truck is riding stock at the moment and have had some wobble issues when hitting bumps at high speeds or water. I am debating on putting a stabilizer on the truck and am wondering the best one to use. I have seen the fox, bilstein and rough country dual stabilizers. Bilstein and Fox being the more expensive. Will rough country hold up to the abuse? I use my truck in all terrain. I like the Fox stabilizer as i am debating putting fox shocks on my truck as well. Would a steering stabilizer help my truck out? Any input would be much appreciated! Cheers fellas!

 

Some folks will call a SS a "Band Aid" will its not! Its is a component in the suspension that has a job to do and does it. But we can make it into a band aid and that is when you add 1 to make 2 or even more, I have as many as 4*.

So if you are running more than one SS and you tire/wheel combo is not extreme then you have entered into the bandaid world. The laters forces that result from normal wear of suspension components will allow DW at some point in time, enough miles and years and it will appear. Adding a second SS will only DELAY DW, it will not cure it! I recommend you go with a good quality HD SS. Do not let money be your guide. I have always run Rancho on my Jeeps and my Jeep builds for clients I ran the Rancho FORD Truck 5401. ( do not know if that is the one you need to run on your truck). I would suggest contacting the ones you like and asking for a HD recommendation for you make and model.

An indication of the 'strength' of a SS or even a regular suspension shock is the diameter of the body of the shock and the diameter of the central shaft.

FOX/Bilstein make there own shocks, Rough Country outsources as do most. IIRC there are only a few shock manuf in the US.

*NOTE: There is some justification for more than one and that is when you tire size (really WEIGHT of tire and rim) become extreme. Remember the purpose of the SS is to modulate the reciprocal oscillation or to just control the lateral forces that result from road impacts, pot hole, water puddles, heat/expansion strips etc etc. As tire and wheel increase in weight the rotating mass gets harder to control so you are justified in adding larger and or additional SS. I was able to run 37" tall BFG KM2's on Walker Evans Beadlock wheel. weight was about 130 lbs gross.

 

Just changed all 4 shocks yesterday (original FX4 Rancho's), 2 were noticeably bad so I had hope. Hit one of the "trouble spots" in the road today @ 55 mph and off she went, shakin' like a beat up old truck. I really didn't think that would fix it but based on the feed back here (which was correct) the shocks were crap anyways so now the Ford Dealership can't blame (and make me pay for) them. Everything else besides the alignment should be a warranty issue as I have the extended coverage.

 

Be sure to let us know how they resolve it. My GUESS, replace track bar, but am very interested to know exactly what they replace and if it solves the issue. I can tell you for a fact that Jeep would do nothing, your jeep, your problem, DW is just a part of Jeep life, live with it.

 

I bent the joint at the end my track bar on my 2011..shook violently. I see what you mean. My 16 shakes over bumps bumps but soon clears upon leaving them.

 

I grew up in a family owed AMC/Jeep dealership and owned Jeeps all my life (10+-) until recently (still have cars) and never experienced anything as bad as this.










When We owned a marina our 1988 GMC 3500 flatbed (last year the one tons had solid front axles) developed it but a new stabilizer resolved the issue.

On this one spot on county Rte 477 that has a full width paved patch about 10' wide it will do it violently every time between 55-65 mph. If you hit it with only the RF it won't do it or slower it's mild enough you can drive out of it. There will be problem knowing when it's fixed.

When sitting still if you jerk my steering wheel back and forth there's a clunking sound that's noticeable every time you change direction.

Because I've never experienced any tire wear I feel initial steering linkage, box or track bar/linkage are prime candidates. I will definitely have them do an alignment @ my expense and add caster.

 

Its a problem that was especially unique to the TJ (97-06).

Here is the Jeep design, they use a tie rod end to attach the Track Bar to the frame side. Coming out the chute the tie rod end wobbles back and forth. So if the castle nut on top gets lose, wears or anything you incur lateral movement, thus you get DW. In this case its OEM and not an option on all TJ, standard equipment and you will get DW on a TJ, can't avoid it. Few dealers will put on a new SS but that does nothing in the long run.







Track bar frame side tie rod end, it wobbles when its brand new, not IF you get DW but when!





Here I cut off the frame side TB mount, note the single hole, where the TB attaches, also take note of the white piece of paper where VIOLENT DW cracked the frame mount. See story below for when/how it happened.





Here is how you solved the issue: TB attached to a grade 8 double shear bolt!

Death Wobble, a story:

While out in Pomona, Ca attending the Off Road Expo I was driving I 10 which is in dire need of repair. The road is rougher than a Nyquil hangover and no ones friend, Death Wobble, is trying to hitch a ride with me at about 70 mph. Of course it picked a great time to do it as I was lifting a cup of near boiling coffee to my lips.

Suddenly I find myself trying to steer, dodge boiling coffee and traffic at the same time. I’ve got 7 or 8 cars around me that are watching the Jeep Rubicon do the Death Wobble 2-step, coffee is everywhere but mostly on the inside of the windshield, my lower lip and between my legs which is causing me to lift out of my seat.

Finally I get the Jeep settled down enough to pull over in the wish I wasn’t here lane. I get out to do an inspection and of course normal cars are whizzing by only inches from my burnt body. At least the wind is making my crotch and lower lip feel a little better.

Turning the Jeep around at the next exit and heading back to the motel to change clothes, and try to figure out what to do about my lower lip. I also need to think about what I can tell my wife that she will believe about why I have a scalded crotch.

 

So here's an update.

I installed new Bilstein gas shocks with no change.

Went in for a 7:30 am appointment (made several days before) that I was waiting for (Parks Ford Wesley Chapel Fl). SORRY, you have to drop it off and we'll get to it when we can. Well, that didn't work so I left.

Made an appointment @ Jarrett Ford in Dade City Fl. for 8:15 am.
Got there on time. Finally @ 9:30 am they said I needed new tires.
I knew I needed them but I assured the tech that wasn't the issue.
noon time I was told the drag link was bad. and they had to order it.

Appointment was made for three days later, no warranty rental as it's "drivable" according to Ford.
A day before the appointment they cancelled it on me and scheduled it for the next week.

Since I had the time I replaced the tires with Cooper RTX's, no change.

Dropped it off and took my rental. Told them to do an alignment also.
I called @ the end of the day and it wasn't ready.
Picked it up the following day.

They replaced: Complete drag link assembly and track bar ball joint end.

The severe "death wobble" ' is gone, but it does shimmy over the the same bumps quite a bit but does come out of it now.

Looks to me like the sway bar bushings are worn as the bar has shifted over an inch to the left. Don't know if it matters but I'll be looking into it.








That's it so far.