Tire Balancing

[pman]

I have 305/70/16 BFG KM2s on my 2001 LX with roughly 40K miles on the tires. Lately I have been having issues with balancing them.

It seems to be one tire that is the problem. Its on the rear and causes a noticeable shaking at 30-40MPH, as I speed up the shaking almost goes away completely. But you can still hear/feel that it is not perfect. I know it sounds crazy to say it sounds like it is out of balance, but there is a difference.

Last time I got them balanced, everything was great for about two or three weeks, Then the shake/noise started to slowly come back. The time before that they were good for a month or so, but again it slowly came back.

This weekend I took off each wheel and checked for mud caked inside the wheels. There was a little bit, but it was minimal and spread evenly. Anyways, I cleaned out the mud, but it didn't seem to help any. Took it to Sears and had them balance all 4 tires. Driving home I noticed that it was still out of whack. Upon closer inspection, I realized the morons left all the old weights on and just added new ones.

Obviously I need to take it back to have them re-balance. However does anyone have any ideas as to why they wont stay balanced?

I have thought about dyna beads, but looking on various forums from a google search the feedback is all over the place. Therefore I am not inclined to try them.

Lastly, anyone think I should pull off the weights myself before turning it over to Sears again?

 

[Sandroad]

How about a good road force balance at a tire place that knows what they're doing? Not removing the old weights is a clear indication of incompetence. Road force balancing is expensive, but it will help identify if there is tire with structural problems causing loss of balance.

 

[inkpot]

There is a chance that this tire has been balanced OK and it just has started failing structural integrity. You may need to delegate it to spare only duty. Not real rare problem for tires with a lot of miles on them. Are they aging out? John

 

[THEROK]

-tire is out of round

-wheel is out of round

-alignment causes tires to wear unevenly

-tire tech isn't doing it right

There are a number of things that could be the sources or sources to problem. You need to cover your bases. I understand your frustration. I have run into these issue with other cars in the past and it annoys me royally.

What's interesting is it'll only get worse when you rotate them and they end up in the front.

 

[TXLX100]

Like others have said, you may just need to take it to a good shop and have a dynamic balance done on the tire. Road force will tell if the tire is bad. Also, a good shop should be able to phase match the wheel and tire to improve the balance. Big tires can be tricky. Of course if you are putting the tires through the ringer it could be slipping on the wheel, but you could see that if you note the orientation.

 

[Tinkerer]

I second the motion to do a road force balance. Total force variation can cause vibration even if wheel/tire are well-balanced, and even if runout is minimal (because force variation can be caused by non-uniformities in the tire section itself which affect the force response due to non-uniform stiffness aka modulus).

With that said, tires are not very stable elements. Over time the tire can change with respect to both runout and section stiffness/uniformity. If the vehicle sits on the tires without rolling for long periods they can even "flat-spot", I dealt with this problem not too long ago with some Michelins bought new for a 4Runner that sat for most of a year.

Look up Hunter GSP9700 Road Force Balancer. Interesting things to note: (1) Tire dealers rarely use one, I believe this is partly due to cost but also partly because they don't want customers to see the poor quality of many tires with respect to road force variation. (2) Dealers usually DO have one. (3) GSP9700 machines are not always in good condition and calibrated, evidently they are also expensive to maintain. (4) Technicians frequently don't really understand how to use them properly, which I attribute to low pay / high turnover / poor training in most shops.

Aside from bent wheels, there is one more thing that can cause tire vibration to develop due to wheels/tires: If tires are mounted using silicone spray as a lube, they will tend to slip on the wheel for days/weeks after installation, throwing the balance off. Using silicone is a no-no, I ran into this problem once some years ago; confirmed it by marking tire/wheel, then made the shop dismount/clean/remount/rebalance WITHOUT silicone.