My XJ Refuses to Run BFG ATs!!

Okay, this is really odd. Can anyone figure out what is going on? Every time I put a set of BFG AT's on the XJ I get major death wobble. I have tried different sets of 33/10.5/15 and always, the XJ shakes so violently I expect the doors to fall off. Swap the 32" swampers back on, & everything is fine! After one episode with the BFGs, I put the Swampers back on, ran 'em 4 hours to Rausch, wheeled and drove back home, no problem. I have swapped 3 sets back & forth always with the same results. One set BFG has AR aluminum wheels, and the other set has Soft 8's. Both load range C, no dry rot, no sidewall bulges ... in fact both sets are like new with nubbies still on. So why won't my Jeep run them? :dunno:

I know someone is going to say the BFGs are bad, but tire shops have told me that they're fine, & they're balanced. Besides I sold the aluminum set & the guy has had zero problems with them. My theory is that the sidewalls can't support the weight of this 4400 pound pig, but that makes no sense.
Any tire gods out there with some wisdom?

Cursed?

Possibly that the Swampers are so out of balance/round that it offsets something bad in the front end and equils out.

:roflmao:

diffrent wheels?, maybe the bfg wheels are bent or somthin. You could also take them to a shop that has a ballencer that measures road force variation, most balencers do not measure this, it puts a "roller" on the tire and tests for imperfections and such in the tire.

Darky said:

Blessed?

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fixed

whitexj98 said:

diffrent wheels?, maybe the bfg wheels are bent or somthin. You could also take them to a shop that has a ballencer that measures road force variation, most balencers do not measure this, it puts a "roller" on the tire and tests for imperfections and such in the tire.

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I can't accept that the steel & aluminum wheels are both bent. Besides, the new owner of the aluminums has no problems. Thanks for the idea, but I'm reluctant at this point to spend money on diagnosing this mess.

I think Darky is on to something. I'm beginning to think my XJ is alive & she's a bitch. If I put any oil besides Amsoil she creates such a ruckus, coughing, spitting, I gotta drain & refill ... but that's another thread.

You didn't think the jeep was a living being before? shoulda known.

Death wobble comes more from your worn out tie rods ends, sway bar brackets, bushings, etc. Are the BFG's bigger, that is probably the case which just makes the wobble happen more because it moves the angles of these rods more into the worn ruts in the tie rods and stuff. How old are your tie rod ends, sway bar brackets, sb bushings, steering stabilazers, front shocks, etc.? I traced down my death wobble slowly that kept coming back until I pretty much replaced all of these because of the wear in them.

hollandbr2 said:

Death wobble comes more from your worn out tie rods ends, sway bar brackets, bushings, etc. Are the BFG's bigger, that is probably the case which just makes the wobble happen more because it moves the angles of these rods more into the worn ruts in the tie rods and stuff. How old are your tie rod ends, sway bar brackets, sb bushings, steering stabilazers, front shocks, etc.? I traced down my death wobble slowly that kept coming back until I pretty much replaced all of these because of the wear in them.

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Rod ends, about 2 years old; SB brackets ... I dunno, but if you mean the discos & links about 1.5 years; stabilizer, shocks all OME and about 4 years old; all bushings are poly and tight, except for the UCAs which are shot. Installing brand new UCA's & bushings by the weekend. The entire front end will AGAIN be checked out then.

The 33s aren't really bigger if you set them side by side ... The Swamper lugs are tall. And like I said, Jeep runs fine without the BFGs.

I can help you sell me your tires problem solvedarty:

Take a good look at the trac bar and bracket!

easy... bfg at's are gay and meant only for absurdly big f 250's and f350's with 20 inch or larger chrome rims that see absolutely NO dirt...also known as pavement princesses

and your xj just doesnt wanna be seen skating on a set lol

With the BFGs you have more tire contacting the road so it grips the road better and your tires are trying to go one way and the front end is trying to go the other. Swampers are softer and dont have as much contact surface on the road so they dont grip the road as well. So no your BFGs are not bad or junk there an awesome tire its just they grip the road better.

Like everyone said double check your front end also check how far you are toed in or out.

you know, mine did the same thing! i went from bfgoodie mudders to the a/t's and my jeep was shakin like a queer in a pickle factory! i swapped tires and life was good.
i also swapped tracbar and got rusty's knuckle to knuckle steering conversion... either way, no wobble till i swapped to the all-terrains.

DW is caused by a dynamic instability at a given frequency. The whole suspension is in fact a tuned system. If you change any major piece of the system to something with a different natural frequency or damping factor, you can shift the resonance point, or introduce multimode instability that is quickly damped. Different tires have different frequencies or damping characteristice. Even changing the air pressure has a major effect.

When you introduce a finite impulse, (hit a bump) the system responds by either damping the response or going unstable and breaking into oscillation (DW). That is why adding a steering stabilizer to dampen the oscillation is many peoples first choice. It tends to mask the underlying problem. It doesn't "fix" anything. It simply hides the problem until some later date when it is the absolute worst time to deal with it.

The bottom line is that for the system to resonate usually takes one or more joints with a significant amount of play.

In order to quickly diagnose a loose joint requires two people. Put a person in the vehicle and have them rock the steering wheel back and forth about a quarter turn. Crawl under the rig and inspect every joint, including control arm bushings. There should be no slop in any joint.

bluejeepkid said:

easy... bfg at's are gay and meant only for absurdly big f 250's and f350's with 20 inch or larger chrome rims that see absolutely NO dirt...also known as pavement princesses

and your xj just doesnt wanna be seen skating on a set lol

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Really kid? just because not everyone wants to run mud tires doesn't mean that at's are bad.

I run 33" BFG AT's. I have been in the mud, and I crawl on the rocks. They are a great tire and I've had no problems with them. I do get a little DW from 48 to 52 MPH then it goes away. I haven't tried different tires. The DW didn't change when I removed the steering stablizer.

kf_chris said:

Really kid? just because not everyone wants to run mud tires doesn't mean that at's are bad.

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He's just kidding. I thought it was funny ...


Well, today I will be having the new UCAs (JKS) done so we'll see what we find.

My JKS adj track bar is brand new with barely 100 miles on it. Again, we'll be checking every single part of the front suspension, links, bushings, etc. I refuse to accept that I can't swap tires at will without major issues. Someone said that the BFGs contact more road surface ... they're 10.5" width while the Swampers are 11.5". Allowing for a miniscule variation in diameter & tread pattern, I'd say that they have about the same amount of contact surface.

I'll be hesitant to put the BFGs back on, but I will report back here what we find. Thanks for all the input so far ... I do appreciate the ideas.

Mighty.Mighty_XJ said:

My JKS adj track bar is brand new with barely 100 miles on it. Again, we'll be checking every single part of the front suspension, links, bushings, etc. I refuse to accept that I can't swap tires at will without major issues. Someone said that the BFGs contact more road surface ... they're 10.5" width while the Swampers are 11.5". Allowing for a miniscule variation in diameter & tread pattern, I'd say that they have about the same amount of contact surface.

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Check not just the track bar but the axle mounting location. It can often wallow out and become oblong. Even when it is tight it will slip back and forth in the whole causing the whole axle to shift side to side. If you have any wabble this will greatly exagerate it.

While what you said about contact patches being similar in size may be true, the style of that contact patch is miles apart. The BFGs will track the road with greater percision and grip than swampers. If your alignment is out they will show it much more than any mud tire simply because of their tread design. Check your Toe in. You can do it in the driveway with a measuring tape. If it is far enough out of alignment the two tires (because they grip better) might be fighting each other for the straight line.


Good Luck

I have this same problem when I run any wild country tire from schwabs. I think they buy only blems like their wheels. I can run bfg at's, mt's, big horns, swampers with no DW but if I use wild coutry's TXR or rvt or xtx I get massive death wobble. I do need new ball joints but everything else is new and tight. Check ball joints that may be the issue.