Tire Balance and Shimmy

[mdsalemi]

Guys and Gals,

This is an update with some new information regarding tires, but more specifically related to "balance".  If you have any shimmy issues, follow the link at the bottom and find someone who has a GSP9700 and the flange adapter.  You will be happy you did.  To find out more about this wonderful machine, surf on over to http://209.176.154.132/index.cfm there's a lot of info on how it all works.

Seems I've been plagued with shimmy all my life.  From my 1979 BMW 320i with its legendary and notorious shimmy, to my 113--I've rarely had a car that drives really smooth.  Happily, this has a good ending as I've found the solution--and have applied it to two cars now with astounding results.  Believe all you read here, as it is all true.

You might recall my post of a month or two ago regarding my praise of the Coker Phoenix tire.  My local repair station, Motorwerks, http://www.motorwerksgroup.com did the mounting and balancing.  However after all was done, I STILL had a shimmy at 70mph! :evil:  I called Sateesh (the owner) back, and he called the Hunter folks (always looking for a challenge)and they suggested an upgrade to his Hunter GSP9700 Road Force balancing machine. He bought it immediately.  The upgrade did two things--first, it allowed the wheel to be mounted on actual studs as opposed to a simple rubber cone, and second, allowed weight specifications to be more accurate by specifying corrective weights on both the INSIDE and OUTSIDE of the wheel.  Most tire balance machines only call for a weight in one place, and that is usually the outside of the rim.

When Motorwerks received the attachment, and the software update to the GSP9700, I went back and we rebalanced all the wheels, and found some errors we were able to correct.  Bottom line?  Shimmy all gone.  Completely.

One very nifty feature of the GSP9700 is the ability to independently measure tire balance issues; wheel balance issues; and tire and wheel combinations--and correct for them as well.  I say balance but that is not quite accurate; it measures road force and this has components called "radial and circumferential harmonics, first, second and third order"  Your average tire-changer at Discount Tire is not going to know anything about this stuff.

How does this work? With my set of new Coker's one of the tires was out of round beyond specification.  The machine compensated for this by locating the low spot on the wheel; then instructing the operator to shift the tire's high spot to the wheel's low spot.  By doing this and recalculating road force, it can sometimes create a tire/wheel combination "in spec" with road force out of a "bad" tire and "bad" wheel.  This feature works best with stamped steel wheels as opposed to machined alloy wheels which tend to be more round and have less "hop" to them.  Despite the fact that this was done, and we did create a working combination, Coker is replacing that out of round tire for me.  I believe their words were "We're not going to argue with a GSP9700!".  Order of placement on the car is important.  The tire/wheel combination with the least amount of road force correction goes on the front driver's side; second on the other front; third on the driver's side rear; and worst on the passenger side rear.

I was extremely pleased with the results.  One very important thing to remember is that all the tires "balanced" and you would not be able to discover the problems with the out of round and road force issues on conventional tire balancing equipment--which is why my 113 had the shimmy all along.  And, had this GSP9700 existed 25 years ago, I'm certain my BMW would have been corrected.  They always said it was a tire issue, but the tools to correct it didn't exist.

Then, the other night, my wife brings home our brand new Explorer SportTrac (chill out everyone she works for Ford!)which had a shimmy at 70 mph.  She noticed it on the way home from work but did not tell me.  My first highway experience with the truck yesterday and I was back in shimmy hell!  So it was back to Motorwerks today, and lo and behold, we found--on a brand new vehicle--two big problems.  First, one tire was out of round beyond spec.  With cast and machined alloy wheels, unfortunately we were not able to correct for it.  We found another wheel/tire so badly balanced in terms of road force that it fooled the machine into thinking the tire was out of round; when we took the original weights off, the problem went away and we were able to get it right.  Luckily the new truck has a full sized spare.  Ironically this tire was nearly perfect and it went onto the front and the bad one under the truck into "spare" service.  So, the shimmy on the SportTrac is gone as well.

Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored

[hauser]

Mike I too have been down the same road as you.  Going from one place to the other trying to achieve that "perfect balance".  My biggest nightmare was with a BMW.  I tried everywhere and even had the tires balanced while on the car.  This is a balancer that works without taking the tire off the car and balance the unit as a whole.  Wheel, tire, center cap and suspension all at one time.  Did not work.  I was getting pissed off until I found a guy that took his time mounting and remounting the tire trying to get a "perfect balance".

When I purchased my ML I did not like the wheels that came with the car and the owner of the dealership got me the ML430 wheels for it.  They did the mounting and balance with all the weights on the inside of the wheel! (which is how the 430 was) Whatever they did and whatever they used worked out great!

I wonder what the car manufacturers use at their factories?

1969 280sl 5 spd        1999 ML320          Gainesville,Fl.

[mdsalemi]

Well Hauser, my suggestion is to go to the Hunter GSP9700 website and find a rep near you; then call or email the reps to ask them who has the GSP9700 in your part of Florida.  There are only 12 of these machines in the metro Detroit area so you may have to travel a bit, but my guess is you'll be as pleased as I am.


Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored

[ted280sl]

Mike,
   That balancing machine is magical. My other car, a Subaru,
has had a slight shimmy for a few years. I put new tires on it and had the wheels balanced by a reputable tire shop. I still had some shimmy so I brought the car back had had them re-balance the front end. There was some improvement but, it did not feel right. After reading your post I brought the car to a repair shop that had the machine you mentioned. He re-balanced the wheels and it really made a difference. No more shimmy!
Thanks,
Ted

[rwmastel]

Mike,

There are 23 shops that use a Hunter GSP9700 within 10 miles of my zip code.  You can bet I'll be taking my cars to one!!!  Thanks for such an inspiring story.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[mdsalemi]

Well guys when I say "Listen to what I say it is all true" I really mean it.  I will NEVER have a tire balanced on any other machine every again--unless of course it is Hunter's follow-on to the GSP 9700.

Note also that the FLANGE/STUD adapter and the new software that comes with it is very important, particularly if you have steel wheels.  Make sure the shop you use has that attachment!


Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored