KM2's balance problem

Help...I bought 5 new BFG KM2's a few weeks ago from Discount Tire and they can't get them balanced. I've been back twice and about to go back in for a third time. They told me if I come back a third time they would put a different brand of tire on for me.

I had the Pro Comp Extreme MT's on my last Jeep and loved them, quiet, balanced nice but thought I would try the KM2's this time.

WTF?? Have any of you had problems with balancing the KM2's?

They're 315/75/16 on Black Rock steel rims both new.

Thanks for any feedback.

My KM2's are fine. Could it be the steelies?

Your wheels are the issue, I bet one is bent on the hub.

You think a brand new wheel could be bent?

Dudetx wrote:

You think a brand new wheel could be bent?

Yes.
Can they balance any of them? If it's just one tell them to replace that tire! I've had problems with BFG tires in the past not balancing and I've made them replace the tires for it too. That's why I went with Toyo this time.

whatever the case, it should not be all 4 wheels/tires

That would beat the law of probability. One, ok. Two, very weird. more than that and something is waaaay off. I haven't seen any posts about a bad batch of KM2s. They should dismount the tires and see how the wheels balance. if the wheels are messed up, then that could be the problem. But 4 wheels & tires NOT balancing is very strange. Try a different discount tire and speak to the manager about the issue.

I had 4 super swamper LTBs. Those are bias ply and are notorious for being hard to balance. 2 of the 4 balanced with less than 7 ounces on cragar soft 8s. of the other 2, one took 11 oz and the last could not be balance properly with 15 oz (almost a full pound )

SWAP Them!!!!!! My dad went through all four tires, blow outs and screwed up his fenders!!! Tires probably have seperation! SWAP THEM! Don't rack up miles on them!!!!

I watched them weight them and they all spec'd out on the machine. Headed back in the AM.

I've heard guys talk about "Road Force Balancing", is that different than what DT does?

I've never heard of road force balancing. I've had my km2's for ober six months and about 7500 miles on them. I had to get them balanced 2 times inthe first month that i had them. but once they got broke in they were fine. but they're on stock 16 x 8 rims so it very well bould be the wheels.

Road force balancing is more for 37 yo 40" tires, not a 33" which is essentially what you have despite what BFG stamped on the sidewall. And it isn't cheap either...$200 plus per tire

from another forum:

A tire is not necessarily round. Its tread surface does not necessarily describe a perfect circle. What is most important is, "Is it round while rolling?" The first step in using a GSP9700 is to measure just that.

A tire/wheel is mounted on the shaft of the GSP9700 and a roller is pressed against the tire as the shaft slowly rotates. The roller presses with a constant force of about 700 lbs (early version) or 1,400 lbs (later version). If the tire is perfectly "round while rolling", then the roller will roll with the tire but will not move otherwise, i.e. there will be no measured "runout" of the tread surface. If the tire is not "round while rolling", then the roller, which is mounted on an arm, will move back and forth, toward and away from the shaft of the GSP9700, as it rotates, i.e. it will measure the "loaded runout" of the tire.

Now, how significant is that runout?

Here is what happens: Suppose the tire rolls along a perfectly flat surface (i.e. a really good road), and suppose its axle is mounted to an assembly that keeps the axle at exactly the same distance from that surface. If the tread surface is perfectly round while rolling, then the force exerted by the axle on the wheel (which, of course, is the same as the force exerted by the tire on the wheel), will be constant as the tire rolls along. As a "high spot" in the tread circumference, i.e. a "high spot" in the loaded runout, rolls into contact with that surface, then the tire pushes upward against the axle with a little more force than average, right? As a "low spot" in the tread circumference, i.e. a "low spot" in the loaded runout, rolls into contact with that surface, then the tire pushes upward against the axle with a little less force than average, right? That variation in the upward force the loaded tire exerts against the axle tries to make the axle move up and down as the tire rotates. In a vehicle, it does make the axle move up and down. It feels like an out-of-balance tire/wheel assembly.

Interesting, huh? The nominal scale factor is that a measured runout of 0.001 inch corresponds to about one pound of "road force". That's where the term "road force" originates.

It isn't enough to just measure the loaded runout of the tire, though. Why not? Because the wheel isn't perfectly round at the bead seating surface, either. You could mount a perfect tire on a wheel that isn't round and you would get the same effect as mounting a tire that isn't round on a perfect wheel.

So, what's a feller to do?

The GSP9700 can also measure the runout of the wheel. It uses a small roller against the rim on each side to measure its runout. Then, with a bit of arithmetic, it can determine how much of the loaded runout at the tread is due to the wheel and how much is due to the tire.

That's what Michelin wants measured. They want to know the loaded runout (measured in thousandths of an inch or in pounds) of the tire. If it's too much, then the tire is defective. Michelin understands this quite well.

So far, all we've discussed is how road force is measured. What, then is a "road force balance"?

Once the operator has measured the loaded runout of the tire and the runout of the wheel, the GSP9700 computes how to minimize the net loaded runout of the assembly. The operator makes a chalk mark on the outer sidewall of the tire and another on the rim, as directed by the GSP9700. He then removes the assembly from the shaft, deflates the tire, breaks the beads loose from the wheel, and rotates the tire on the wheel to align the two marks. Then he re-seats the beads, re-inflates the tire, and re-mounts the assembly on the GSP9700.

What this does is mount the "high spot" of the loaded runout of the tire at the "low spot" of the runout of the wheel, which minimizes the net runout of the whole assembly as measured at the tread. The proof is in the puddin', as the saying goes. The GSP9700 re-measures the loaded runout, at which time the operator can see just how much better it is.

It is not necessarily going to be perfect, because the loaded runout of the tire does not necessarily equal the runout of the wheel. The procedure is more correctly described as a "compensation" than a "correction", as one defect is used to compensate for another.

That procedure is called a "road force balance". Note that a road force balance has nothing to do with mounting weights on the wheel. Once the road force balance is completed, then the whole assembly has to be spun by the balancer, its imbalance measured, and weights applied to correct the imbalance, in the usual manner.

The result is that you can have a wheel/tire assembly that has significant road force imbalance but is in perfect weight balance, and you can have a wheel/tire assembly that has significant weight imbalance but is in perfect road force balance. Either condition can cause vibration that you can feel. You gotta get 'em both right, and it takes a separate procedure for each one to do that.

But, you can't get road force balance perfect, as I noted above. How good is good enough? Usually about 25 lbs of road force imbalance is a threshold above which you can begin to feel vibrations from it.

Is this real? Damned right it is. EVERY wheel and tire put on new vehicles is road force balanced at the factory.

take it to southwest brake and alignment. they can shave it into a perfect balance.

Well I don’t have a problem with them, they balance fine for me. Now on my other car (my DD) discount tire can never get the balance right so I don’t take it there anymore plus they always break my studs there, well actually twice but that’s enough for me. So take it somewhere else before you start changing tires.

Firestone does road force balancing... not all locations tho.

call the Fort Sam location 224-0209. Ask for Richard Martinez. He's the store manager. Tell him you are in the jeep club with his son (Richard, that's me). Tell him about your problem with balancing. Not sure on the price for road force balancing, but you can ask. he'll do his best to get you taken care of.

(disclaimer - This location is uber busy. you might have to be there on a saturday at 6:50 am before they open if you want to wait for it. Also, he can get you a great deal on some Destination MTs. they kick a$$. then get ur $$ back from discount).


good luck.

Update...the rims are out of round!!! Ordering new rims today (aluminum this time!) and will deal with Quadratec and Black Rock after i get the new rims mounted.

I guess I should have known better than to try the steel wheels...DAMIT!!

Thanks for all the feedback.

MC

try river city offroad. Marcus can get you a good deal on just about everything jeep related.