Wheel Runout - Balance Problem

[GR8_ASP]

Just purchased replacement tires and found a problem. Neither rear wheel can be balanced due to excessive runout. These wheels have never been damaged in any way but show the same symptoms - each has nearly 1/2 inch of runout (in and out, pependicular to rotation). The tire shop tried to load balance them and said it was not possible. What do I do? The wheels are production polished wheels for 1996.

Thanks,Ron

 

[Ulysses]

A little ditty I found:

"Usually, runout can be reduced to acceptable limits by relocating the wheel and tire assembly on the wheel studs or rotating the tire's mounting position on the wheel to put the high point of the tire at the low point of the wheel. This latter procedure is called match-mounting a tire. Chrysler 22-01-97, 6/13/97"

By John Fobian

Hope that helps,

Ulysses

 

[GR8_ASP]

Clarification - the runout is the wheel and not the tire. It is also in the side to side direction as mounted on the car. I believe the balancer mounts the wheel against the backing plate and uses the center circle for centering. I am pretty sure this is a wheel issue and related to hub squareness.

Ron

 

[Ulysses]

The earlier statement applies "Usually, runout can be reduced to acceptable limits by relocating the wheel and tire assembly on the wheel studs " if the hub also has runout. Then you are match mounting the wheel against the hub. The first thing to do is confirm that it is the wheel. If you go back to the same tire shop. Have them check that the balancer back plate is truly square. If it is, then you can match mount against the hub and balance on the car. Or you can try a different tire shop and see if they come up with the same results, letting them know that you suspect excessive wheel runout so they can give you a second opinion. Sounds like its going to be pretty much trial and error.

Anyway, if it does turnout that the wheels have too much runout on the sides, going through matching can be time consuming and may not solve the problem completely. Very frustrating. It would probably be just easier on you now and later down the road to give Jon B a call and get new rims if you confirm that it truly is the wheels.

 

[Trbulnc]

One question for you, I work for a wheel manufacture so I might be able to offer a little insight. You said you had lateral run-out of .5? Is this what the store measured at the highest point? Lateral run-out is an average taken over the reading of the entire wheel. Usually if there is .5 to one side, 180 over will be leaning the same direction to an extent. (due to the cnc machining process and the offset of the bolt pattern or hub hole depending on how the wheel is chucked. This will help offset the .5 from the other side. Lateral is checked on the A1 side which is the side the viewer sees on the car and A2 which is the inside of the wheel. These two averages are taken together and then calculated together to get a run-out total. The A1 and A2 both have a higher run-out spec than the lateral average (overall combined). Sometimes a print does not call out for a lateral tolerance so it becomes a in-house spec set by the manufacturer. If it is just a highpoint of .5mm it isn't necessarily that bad but if it is an average that could be bad! A common setting for A1 and A2 measuring device is 1.0 mm run-out. When the two are combined for an average, lateral can be up to .5, .6. have seen upwards of .8 on some products. Different manufacturers have different specs with GM having one of the toughest of all competitors. On a side note...if the wheels were purchased as aftermarket over the counters that could explain also. If a wheel can not meet the run-out spec. for production but are very close, they are sometimes kept as service parts to be used as insurance replacements, over the counters, etc. Some companies service part orders do not have a tolerance as tight as production wheels.

 

[Trbulnc]

sorry, made a typo...if it is .5 in a direction (say upward), 180 off should be about .5 downward...in the opposite direction. Not always true but usually aids in countermeasuring.

 

[GR8_ASP]

Thanks to everyone for their helping words. Based on the comments above I installed the wheels on the car and checked the lateral runout installed. I was surprised to find it within a mm or so. I also drove the car ever so slowly (God that is difficult in the Viper) while watching the wheels in the side mirrors. The rear quarter panels provide an excellent background for comparison. No significant runout driving either.

It appears the whole issue is the mounting of the wheels on the balancer. This is a Hunter 9700 (load balancer) so the balancer is not the issue. I believe the issue is that they have no 6 bolt mounting plates and revert to using a backing plate and cone on the inside diameter. I described this to the Viper Team tire and wheel engineer and he thought it should be okay. But, evidence would indicate that it is not. The store, Discount Tires, stated they would do a search for a better mounting solution. I hope they find one.

I did a test drive and did not find any noticeable vibration. Only had one quick burst up to 120 or so do to heavy traffic. Will try more later.

Thanks again for the help. Note Discount Tire has been helpful and courteous throughout so even if it is their problem I believe they will find a good solution.

Ron

 

[GR8_ASP]

PS. The lateral runout specification is 0.8 mm. There was no indication of an average runout. This is circular runout per side. Mounted on the car mine appear to be within that amount.

Ron

 

[John Moore]

I see comments on "1/2 inch" runout and .5mm runout. Which is it? A "1/2 inch" is incredible and would require no equipment of any sophistication to detect. If you put a wheel on the car and spin it and it doesn't look like it's wobbling all over the place then the mechanic at Discount hasn't a clue how to put a wheel on the balancer. If they are wobbling all over then they're bent big time. If it's .5mm then you can confirm this easily by placing a screwdriver on a jackstand and point the tip right next to the rim edge while the wheel is spinning. You can see the rim rotate in and out towards the screw driver.

 

[GR8_ASP]

The initial statement by Discount Tire was 1/2 inch of lateral runout. They placed it on a different balancer to demonstrate it to me and yes it did wobble by more than 1/4 inch. The setup was repeatable for both rear tires on 4 different balance machines. However, they used the same setup method each time.

I confirmed the as-mounted runout of less than 1 mm as you indicated. I ran a string across the fender and scaled the gap at several rotational points. It was less than 1 mm, without any question.

The primary difference between the balance machine setup and the vehicle is the use of the wheel center for the machine and the 6 lug nuts on the vehicle. Both contacted the back of the hub. I still do not see why their method produced such erroneous results.

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But now that I have confirmed the wheels are straight the ball is in their court to find a way to mount and balance them properly. In the meantime it drives well with no apparent vibration problems.

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Ron

 

[Cam]

Sounds like the is not setup on the balancer properly or maybe cant even handle the offset of the rear wheels.

 

[Trbulnc]

Has to be in the machine or the way the wheels were mounted. A lateral run out average of 1.5mm or greater (about .060" and up) will produce a very bad vibration that will not balance out usually. You would not even be able to idle down the road with a 1/2" run-out. A tire also seats on a flanged area on the the dropped portion of the edge called bead seat. If there was 1/2" run out the tire would not seat properly and would more than likely not hold air. The flange is to seal the bead and protect the tire from exploding when damaged. There is a 1st harmonic and concentricity spec. which is the relationship between the hub hole to bolt holes (how far off center they are from each other). This will also cause run-out problems, but it has a spec from the manufacture also.