From digest.v7.n292 Wed Sep 17 18:30:08 1997
From: Lowell Seaton <SEATON.LOWELL_at_EPAMAIL.EPA.GOV>
Date: Wed, 17 Sep 1997 18:36:44 -0400
Subject: Wheel shimmy and tire balancing

There has been quite a bit of talk on the Digest the last couple of months about wheel shimmy and steering wheel vibration. My experience may not apply to all BMW's, but I know that my '95 M3 is hyper sensitive to out of balance front tires. I had 17,000 highway miles on the original Michelin Pilot SXX's, but I had hit a construction work zone at 15,000 miles that bent all four rims and probably broke the belts in the tires too. Then I thought, what the hell. Might as well do an autocross on used tires before I buy new tires. At said autocross I completed a judge's score 5.9, 8 cones DOA, 2 =BD revolution spin at 90+ mph, thereby flat spotting what was left of my tires. Did I mention? Never lift the throttle in an E36 M3 in a fast sweeping corner :-)) <bg>

After all this, my steering wheel wobbled worse than Duane C. after drinking a 6 pack. I went to the local Discount Tire Store for new Pilots. (BTW: My local Discount Tire Store sold me the Pilots for exactly the same price as Tire Rack. I paid sales tax but then I didn't pay shipping from Tire Rack so it was a wash. Very satisfied with Discount Tire price. However, the grease monkeys did way over torque my lug bolts. Must have torque the bolts to 200 ft-lbs That's an old thread. You just can't get good wheel mounting at any price. Sigh.) With new and balanced tires, I thought my steering wheel shimmy would be gone. But no It was nearly as bad as before. So I called a local BMW performance shop recommended by my local BMW club to get a wheel alignment. I thought I must have knocked it out of alignment when I bent the rims.

I called the performance shop, described my wheel shimmy, and said I had new balanced tires on the car. Before I could tell him I thought I needed a wheel alignment, he said that discount tire stores have a hard time properly balancing tires. I took my car in. He rebalanced the front wheels. Never touched the alignment. Afterwards, I had absolutely no steering wheel shimmy. It was an expensive wheel balance, $50 for 2 wheels but he was right. I asked him what the key is to balancing wheels because I thought anybody could balance wheels with these new computer spin balance machines. The mechanic (he also owns the shop) said that tire balancing machines need to be periodically calibrated. He calibrates his machine every morning. I'm sure Steve D'G will concur that you can have the most sophisticated tire balancing machine in the world but if some 17 year old tire jockey drops a tire iron on it, it isn't going to work properly.

LESSON LEARNED:

Pay your money and get your tires balanced by a competent, caring mechanic. Expect to pay for half an hour of labor per tire. Ask how often the tire balancing machine is calibrated. If the mechanic doesn't say daily, go somewhere else. Don't go to any place that has 17 year old kids working around. No, I don't want to rehash that idea of taking all the E36 M3's away from all drivers less than 30 and giving them only to experienced drivers. I am sure that there are 17 year olds that can balance tires exceeding well. But think about it, where do you want to take your chances. At a cheap and fast tire store with part time kids working their way through school and minimum wage laborers or at a BMW specific repair shop owned and operated by a 46 year old man who worked his butt off for somebody else and saved his money to buy his own shop. I know who will be balancing all of my tires as long as I live in Dallas.

Other advice:

1. Leave your BMW at home.
2. Jack it up, put it on jack stands, remove wheels (2 or 4)
3. Put the wheels in your other car or borrow a friend's RM3DR1 M3. I hear they can get 5 R1's in there and don't even need tire baggies :)
4. Shop around locally and get a good price on your new tires. Ask the local BMW club if any tire stores give discounts to BMW club members. You might be surprised that you can get tires just as cheap as mail order. If not, take your mail ordered tires to a tire store and have them mounted. Don't leave. Watch every move they make. If anybody uses a steel tire iron on your rims, grab a tire iron and break their fingers. The Discount Tire Store that I used had a really neat Hunter tire machine. It just rolled the tire off the rim. No tire iron touched my rims except to pull the carcass up and out to hook it on the machine. Really nice machine. I think nearly every tire store has at least one of these machines. But don't turn your back. I am afraid that the tire jockey would use the quickest, closest tire machine if you are not there to watch him.
5. Don't pay to have your tires balanced by the discount tire store.
6. Take your wheels to a reputable BMW repair shop for balancing.
7. Take your wheels home and mount them yourself. Torque the lug bolts with your own well maintained torque wrench. 74 ft-lbs (i.e. 100 N-M) should do it. Be sure to back the torque setting all the way off before you put the torque wrench away.
8. Lower the car, drive off and enjoy. Your wheels will thank you.

If you still have steering wheel shimmy, I think you can eliminate out of balance tires as the problem. You may need to check the wheel alignment next.

Lowell Seaton
'95 M3 (w/ balanced but scalloped tires - don't take your new tires

to driving school ;-)