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Wheel Balancing - When first try doesn't work - READ ONLY

68 messages,  Last post on Aug 17, 1999 at 7:29 AM

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Messages Page 7 of 7

#59 of 68 by quadrunner500

Aug 07, 1999 (4:37 am)

0.010 ounces is impressive, but what good if weights don't come in all increments. You put on the smallest 1/2 oz weight, and with the rounding error, you're nowhere. Not saying it hasn't worked for you, but must admit I have some doubts that a wheel balanced to 0.010 ounces is going to stay balanced that way for more than a few scuffs of the tarmac, or a few miles. Hope I'm wrong.

#60 of 68 Small weights by vivona

Aug 07, 1999 (3:13 pm)

The GSP does come with smaller increment weights. The idea of balancing down to such a small weight is to allow a lot of latitude for changes brought about by scuffs, mud, etc. If you balance down to .25 oz and it happens to be at the end of the range, then any changes may cause an imbalance. But if you are balanced right down to the .01 oz, you have a long way to go either way before you are even at the level you would be if you had balanced down to "only" .25 oz.

#61 of 68 by quadrunner500

Aug 07, 1999 (5:16 pm)

Well, the proof will be in the pudding. Let us know. Good luck.

#62 of 68 Nagging inconsistencies by quadrunner500

Aug 12, 1999 (6:22 am)

Now supposedly, indexing the tire on the rim can be used to offset the runout of the rim, to cancel the runout of the tire, by putting the two offsets 180 degrees apart.


Now in the Vivona case, we are told this technique was used to cancel a tire runout of 0.035 with a wheel runout of 0.004 inches. Since the wheel run-out becomes -0.008 when put 180 dg out of phase, added together a tire run-out of 0.027 remains. Thoughts?


Then we are told that the superior balance accuracy of the GPS9700, down to 0.010 ounces is relevant, since special weights in small increments are available.


It was stated that in the Vivona case, other more traditional balance methods were unsuccessful, and that the Mitsubishi is more sensitive to vibration due to various suspension and design factors. Not disputing that, but the question remains, how was the benefit of the GPS9700 balance machine germane to Vivona's case when the wheel weight increments applied were stated to be in the range of 0.5 to 1.5 ounces? Are we to believe the coincidence that the imbalance condition was exactly offset by 1/2 ounce wheel weight increments, with no rounding error? Or were these weights a non-integer decimal for some size in between?


All in all, I'm still a bit doubtful that beyond identifying some out-of-round tires to be discarded, the more conventional spin balancers should be able to adequately do the job, if in good working order. Since I suspect quite a few aren't, I might continue to state the case that a simple bubble balance, used on a good wheel, with a modern tire of good balance distribution and roundness in general, is also capable of doing a good job with its inherent simplicity.

#63 of 68 GSP 9700 Advantages by vivona

Aug 12, 1999 (11:54 pm)

The main advantage of the GSP9700 is in its ability to detect variations in sidewall flex. No amount of bubble balance or traditional spin balance will identify a vibration caused by a variation in the sidewall. The tire can be in perfect balance, and be perfectly round, and still have variations in sidewall flex due to manufacturing variances.


The second advantage is the ability to balance down to a smaller weight increment. On a FWD car with an independent suspension, the rear wheels often have little in the way of unsprung weight. According to the article at http://www.dsm.org/how-tos/wheelvibrations.htm accuracy to .25 oz could leave you with an imbalance of 1/2 lb in force at 65 mph. When the unsprung weight was much higher on cars of yesterday, that amount of imbalance usually wasn't detectable, but with multilink suspensions, aluminum suspension parts and alloy wheels, a modern car can feel such a small imbalance.


The proof is in the actual experience. Three attempts at traditional balancing, and two tire replacements didn't cut it. The GSP9700 did the trick.

#64 of 68 Will Tire "Force Variance" Become Well Known? by spokane

Aug 13, 1999 (7:56 am)

Quadrunner points out that other than identifying tires that must be discarded, the pre-GSP9700 balancing technology can do a very good job. I agree.
 
Viviona's case demonstrates there are occasional tires that are dimensionally good and are properly balanced but do not operate smoothly on the road because of irregularities in flexural rigidity. While it is sometimes possible to play off the rigidity problem against balance or runout, this problem often requires replacement of the tire.


When using properly-calibrated conventional balance equipment on a tire with a "rigidity" defect, we can use the process of elimination to set this tire aside and try a replacement. One problem I see in this process is that the alternate tires of this brand, style, and size in the dealer's stock my be infected to some degree with this same problem. With its "force variance" determination, the GSP9700 allows measurement of all three driving-uniformity criteria (dimensions, balance, and rigidity) which can effect ride quality.


Looking to the future, suppose I have a problem with a new tire purchased at Joe's. Joe tries unsuccessfully to correct it using his conventional balancer so I then go across town to Sam who has a GSP9700. Sam finds the force variance to be out of limits. Now, Joe is a good tire guy but he's never heard of force variance so I imagine it could be awkward to ask him to replace the tire. Hopefully, other balance equipment makers will soon join Hunter in having force measurement machines and will acquaint all of the tire shops with this technology even if they don't sell the new machines right away.

#65 of 68 Force Variance by vivona

Aug 13, 1999 (4:32 pm)

In time I think the force variance method will gain popularity. I asked the Goodyear dealer if they had heard of them and they said, Yes, but at $10,000 apiece, we just can't justify buying them. However, the Goodyear dealer didn't have a problem at all replacing tires that were shown to be defective by my Mitsubishi dealer's force variance machine. I did have a vibration problem Goodyear couldn't solve, so having someone else come up with a definitive solution was to their advantage.


Hopefully, as other balancing manufacturers come out with similar machines the price will come down to a level that more tire stores will consider reasonable.

#66 of 68 by quadrunner500

Aug 13, 1999 (5:24 pm)

Vivona, that's where I have a problem, "the proof is in the experience" as a blanket to write off other explanations.


Your case keeps raising more questions. And I realize you went to extraordinary length to be thorough, including measuring runouts.


Here's one problem. Please correct me if I'm wrong, but you said that Goodyear admitted to some bad tires, and gave you a second replacement set, your third set overall, balanced by them, that left you with a vibration that remained. Then you took that set to a business operating the GSP9700, and Mitsubishi paid for it. So the third set was both cause for a vibration when balanced by Goodyear, and was removed as a cause for vibration when balanced by the GSP9700. Same set of tires. Beyond indexing it on the rim to correct for 4 thousands of wheel runout, all it can do is balance correctly if it's not telling you to replace a tire for sidewall variance.


Now think about it. If the GSP9700 said put 1/2 ounce at 12:00 o'clock, and you put a 0.500 oz weight at the proper location, you would zero out the error. Great! But if the GSP9700 said put 1/4 oz at 12:00, and all you had was a 0.500 oz weight, then your wheel would be off by 1/4 oz whether you added the weight, or not. My point is that a standard balancer can balance to that accuracy. And I'm not missing your point that the GSP9700 can additionally identify sidewall variance, and index the tire to offset this against wheel runout. But with your negligible wheel runout of 0.004, you were left with 0.027 for the tire(s) you accepted.


Spokane, I agree. Well said.

#67 of 68 Balancer weights by vivona

Aug 14, 1999 (1:34 pm)

If the GSP9700 said put 1/4 oz at 12:00, you would put 1/4 oz at 12:00. It is pointless to ask what would happen if "all you had was a 1/2 oz weight" since putting the wrong weight on is not an acceptable practice. Actually, if this situation really happened, the tech would take a 1/2 oz weight and cut it to half size.


It is a better argument to say what if the GSP9700 indicated that the weight should be .37 oz. With the GSP9700 you must stock many more weights in small increments, so you would have the .37 oz weight and install it. But a regular balancer couldn't measure to this accuracy and would either indicate .25 oz or .5 oz, depending on where the machine rounded to. In that case you would be .13 or .12 oz off, depending on the round off. That is enough to cause vibration on some suspensions.


The GSP9700 does have other advantages. It has an automatic mounting mandrel tightener to assure that the wheel is mounted tight enough and sensors to detect if the wheel is not mounted correctly. When balance problems are noted, the machine has a display screen that tells the tech exactly what to do. On a standard balancer the wheel or tire could be way out of round and the tech wouldn't even know if unless he actually looked under the balancer cover and estimated the wobble. They don't even have a runout gauge, they just do it by eye. I have watched many standard balancing jobs and never saw the tech watch the tire for runout except in the one case where I had a specific complaint about balancing that didn't work. And they did it by eye. And they mounted the wheel incorrectly, giving a false indication that the wheel was out of round. And they improperly indexed. And the tire still vibrated. And the GSP9700 found all the errors and corrected the vibration.


Works for me!

#68 of 68 by quadrunner500

Aug 17, 1999 (7:29 am)

Okay, fair enough, but one more question, still unanswered.


Were the ACTUAL weights used on your wheels, that you stated earlier to be 1/2 to 1 1/2 ounces, were they in between those amounts, or were they exactly 0.5, 1.0, 1.5 ounce weights? Because if you tell me they were trimmed, or one was 0.66 ounces, etc., I can let this rest. But I would have to remain skeptical of the likelihood that all 4 wheels actually zeroed out if standard wheel weights in 1/2 ounce increments were used.

Messages Page 7 of 7

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