why do tires go out of balance?
 

My understanding of the need to balance tires is as follows: tires are not manufactured with perfect weight distribution and thus a weight is added upon installation to avoid an assymetric force on the tire.
What I don't understand is why, once you add this weight with the initial installation, the tires would ever go out of balance. Do the tires rotate over time on the rim? If this were the case I would think a clever person would have figured out a way to attach the weight to the tire itself thus removing the need for future balancing.
My tires need a good balancing, but I am going to need new tires in about a month anyway, so I'm putting it off. This is what I think about as I feel the gentle vibration all the way to and from work each day.

You are missing a key point.

What about tire wear and alighnment? Tires develop wear patterns that are
not even. So if the inside wears more than the outside the weight distribution changes. Also a worn tire becomes more sensitive to the road because there is less rubber cushioning.

Steve

taking a railroad track at 60 isnt gonna help.....

It doesn't take 60MPH. I just had mine balanced and 2 weeks later went over a RR crossing with a small pothole after it at about 25MPH and heard something go whizzing off and hit the curb...sure enough when I stopped I saw the weight had broken off...so that tire is out of balance again. The weights sometimes just fall off. $12 a wheel for two weeks of vibration free driving:mad:

No tire is perfectly assembled, so the belts are always a tiny bit off true center, and always a tiny bit off perfectly radial. The rubber is never perfectly even consistancy nor perfectly distributed, so as the rubber wears off the tire, the compensating weight added becomes too large or two small as the weight distribution of the tire changes.

Add to that the fact that tires almost never wear perfectly evenly, and there to go -- out of balance.

Impact damage makes this worse, so do bad shocks (cupping) or misalignment of other types, or heavy cornering.

Just a fact of life -- get them rotated and balanced every 5000 miles or so, and they will both last longer a ride better.

Peter

Talking about tire balancing, it seems that the tire weights you get at the typical tire store never fit as well as the original metric weights fitted at the factory. While washing my wife's C230 yesterday, which had new tires just about a month ago, one of the wheel weights felt loose. I was able to pull it out by hand.

Because of this, usually I ask for stick-on weights (from inside). This means before going to the tire shop I have to remove all wheels and clean the inside of the rim. The tire store jockeys will just stick the weights on all the accumulated brake dust, and you'll be lucky if it's on there by the time you get home.

If you go the the Mercedes dealer for tire balancing, do they use the original metric weights?:confused:

Harry, it's best to have wheels balanced at a MB dealer ... the Service Department uses 2-piece MB balance weights ... at least on the wheels for our 1991 and 1992 300CE's and our 1998 E320. Newer wheels with the smooth edges may require stick-on weights, but I would expect the dealer techs to clean the wheel, as required, so the balance weights stay on under normal driving conditions. The MB dealer may charge a bit more than the local tire store, but the job will be done correctly ... and the balance weights will be appropriate for a MB wheel. It's the little details that distinguish a MB enthusiast from a person who merely drives a MB.

When I picked up my 95 SL500 it had a terrible wobble at about 65-70mph. I took it to a local place where the owner is known for suspension expertise on race cars. They even took a couple of the tires off the wheels to reposition them on the rim to get near perfect balance. They spent about 2 hours and it cost me $60 bucks but the results were worth it.

Back to the original post..many tires WILL move on the rims & that will change the balance

You can prove that by marking the rim to tire position & see how that position changes.

Thanks everyone. Some really good points. They seem really obvious to me now that you mention them, but I just couldn't wrap my head around it the other day. I promise to have my tires faithfully balanced from now on.

Eric,
That was a very thought provoking question, and you got a lot of very good answers. MB Doc was right about tires moving on the rims. This is a problem with racers. You have also reminded me of another thought provoking problem. Take any section of freeway, parkway, beltway, turnpike, or whatever you call it where you live. Millions of commuters are wearing their tires out on these roads. Shouldn't there be like piles of rubber dust lining these roads? where does it go?

Thanks a lot
 

That was a great question and the answers were very good, too. I appreciate the expertise and the willingness to share it here that you guys have.

I'm a salesman and I often ask other salesmen why their product costs the price that they have quoted to me. They usually take this to mean I think their price is too high and that they should lower it to get my business.

Really, I am just trying to give them an opportunity to "sell" me. You guys have "sold" me on why it's worthwhile to pay more for something like tire balancing. thanks.

Live or work near a highway and you get a dose of tire dust and (worse) brake dust everyday.
Ever look at a cabin filter from one of the newer MB's? Thats much of what you see on it.
Interesting anecdote:
They measured high concentrations of copper in a reservoir around here and called in experts to find out where it was coming from. They traced it back to the brake pads on cars that run along city streets in the area and were able to show that the friction materials in pads contain bits of copper. It turns out that is a common additive in Japanese and German car manufacturers. It all winds up back on the ground and off to who knows where when the wind blows and the rains fall.

Dieseldiehard,
I agree with your thinking, but you've got to get Americans away from their belchfire V8s. They will sacrifice other things to drive SUVs. You also live in the Bay Area. You've seen lone commuters in their expeditions. I had to road test a Hummer yesterday and what a POS. It's noisy and rattles. At least their ads are reaching their target market. If you watch them, you'll see they are aimed at people with low self esteem.