The shimmy issue - Road Force Variation

Hello everybody,
I hope you can help me with some new ideas to find the source of shimmy on my 2002 745i. I am focussing on Road Force Variation as you can read below, but should I do that or are there any other areas to look at???

I bought the car about 3 months ago and at that time, it did drive a little nervous at speed and tend to shake the steeringwheel on braking, but it had no shimmy at constant speeds. I thought the cullprit were the worn Michelin tires a the front and perhaps slightly warped brakedisks.

But from the moment I touched the front axle, this turned into a shimmy problem at approx. 120km per hour (75Mph). In the past months did several thing that to my knowlegde should elimate this problem but without real succes.

I invested in new Kumho tires on the 19 inch original alloys, but that did not solve anything. I had them roadforce balanced and the numbers weren't great, so there was not much of improvement. Unfortunately I do not remember the numbers.

I replaced the upper and lower control arm. At 175.000km that was for sure a good investment since the bushings did not look so well anymore. Unfortunately it only reduced the shimmy.

I had the front axle realligned (since I replace some components) but that did not change anything

I checked axial runout of the brakes and wheel hubs and found proof that is not the problem:





I switched to my wintertire set, but that was no solution. However, mounting the most worn tires on the front gave the smoothest ride so for.

I had 2 new Continental wintertires mounted on the front axle. They sit on original 18 inch rims and it drove worse then ever!!! I had them roadforce balanced and paid good attention what they did. One was above 120N (27lbs), the other wasn't. After some rotating they became 110N and 85N which is not very good in my opinion.

After 300km (180 miles) went back to the tireshop and the measured the roadforce variation again and now it was about 80N for both wheels, but 70N was in the tire and the wheels are as round as possible, so there is nothing they can do to improve it.

The shimmy is nothing extreme, its just there. Sometimes it is barely noticeable, but most of the times obviously present. 118-122kmh seems to be the sweetspot, but at 105kmh I can already predict that it is going to shake at 120kmh.

Is 80N (18lbs) too much for this car, or is there something wrong with the car and what could that be?

Thank you very much for reading my story!

Arjan

Sorry to hear. Silly question cause you have done alot of work already, but have you had an alignment done on the car? Have you checked to front suspension? How does it feel over speed bumps? Have you tried changing out the front rims? If you are feeling it when you apply the brakes it is in the front for sure. It acts like its something in the rims/tires though... I would start with alignment, diff rims tires.

Originally Posted by TUF-FKR

Sorry to hear. Silly question cause you have done alot of work already, but have you had an alignment done on the car? Have you checked to front suspension? How does it feel over speed bumps? Have you tried changing out the front rims? If you are feeling it when you apply the brakes it is in the front for sure. It acts like its something in the rims/tires though... I would start with alignment, diff rims tires.

Ok, sorry I re-read your post. You have done alignment. This leads me towards a bent front rim or bad front suspension.

Does it pull to one side while under the brakes? How big is your spare tire? Try running your spare tire on the front and see if the problem changes. Swap sides with it. Thats a cheap troubleshooting method (if your spare is full size).

Also, if you have the old set of tires still inspect the tread on them and see if there are un-usual wear patterns on one of the tires. "Tires tell no lies"..

The spare is an 18inch wheel, identical to the winterwheels. With those wherls, I swapped from front to back and also the "new never used before" spare wheel has been on the car. When the new tires were entirely new, they were the worst, but now, all possible combination give about the same amount of shimmy. The spare does not make any difference. The 19 inch summerwheels have different width on the rear and the tires are directional, so they are not suitable for experiments.

The front shocks do feel a bit softer then the rear. But it does not feel as if something is wrong. In terms of ride quality, I would never consider to replace them. Can worn shocks make a car more sensitive to shimmy? If so, I would like to understand that.

What I do notice is that if I hit a large hole in the road at shimmyspeed, the steering wheel shakes pretty violent. That is, compared to my other cars at the same speed, at the same hole.

I had a lifted truck with 40" Tires. As I experimented with different brand tires, radial/non-radial, different tread patterns, etc.. The front end characteristics would change dramatically based on tire. I could have the same symptoms you describe, especially on the brakes. Some tires could not get balanced right due to limitations of balance machines. Changing to a radial tire with a different tread pattern (Tire balancer friendly) made it feel like a different truck, noise, vibration, gas mileage..

Good luck. There isnt much left to rule out..

Well, since some many things have been ruled out, this brings me back to the orginal question:

Is 18lbs or 80N of RFV too much for a e65?

Over here in the Netherlands, road balancing equipement is very rare, but since there are many more shops in the US and Canada that have a Hunter GSP9700, I was hoping to get some number via this forum. What RFV do your wheels have and does it give a smooth ride or not?

I have: 245/50R18 tires on original style 93 BMW wheels

Front axle: 80N (18lbs) both left and right

Rear axle: 105N (24lbs) on one side and 25N (8lbs) on the other side

This gives a little shimmy in the steeringwheel and no noticeable vibrations from the rear axle

Three of us here had similar issues, search for "vibration" or "shaking". Two of us had tire issues -One member had overinflated tires , and on mine I had three defective tires.. Waiting to get them changed out. I found this out when I got them road forced and re-indexed. The third member traded his car after numerous parts were replaced.

Hello First_745i,
Thank you for your reply. What kind of defects do your tires have? Excessive RFV, or something else? If so, I would love to know the range of RFV of these defective tires and how you experience the problem. At what speed and how bad is it.

I did experiment with the tire pressure. Between 2,0 and 3,0 bar the shimmy remains the same. Only real difference is that the ride becomes very firm above 2,7 bar.

Trading in my car... that is not an option (yet )

Arjan

They found issues ranging from excessive road force values, out of round tires and after re-indexing the tires still had excessive RFV. Unfortunately, I didn't ask what those values were. I had shaking in the steering around 40mph and shaking in the seats at low speeds up to 60-65mph. At 80mph it was smooth as glass.

Is it possible that the source of these vibrations have to to with the self leveling system. I'm not a master tech or even a tech lol, but my guess is that this system is the source.

Only my car does not have a self leveling system. My car not even has Dynamic Drive, it has the most traditional suspension available on a e65.

This front end shimmy is really driving me nuts...

Since my last post, I went back to the tireshop for several times. Everytime there was imbalance present and everytime that was corrected. Everytime the RFV went down by itself and now both are below 15lbs. Sometimes the car drove better after such attempt, but it never really went away.

Interesting however is that I started to notice that there is a realationship with temperature. It is worse when warm. When temperatures drop below 7C it is much better.

Then I went to the BMW dealership. They rebalanced the tires again and did find 10g imbalance in one tires which they identified as the cause. For a full and pretty cold day, the shimmy was gone, but guess what... today it was 14C and the shimmy was back. Not as bad as usual, but it was there.

Now I have a choice. The tireshop offered me to swap the Conti's for Michelin. That will cost me 150€ in price difference and it will be their last attempt. If the shimmy is still there after the swap, that will be my problem. What would you do?

Not sure if this will help, but attached is the Suspension section of BMW's technical training for the E65. Note this is from 2002 and some changes may have occurred since publication.

I assume your tie rods have been checked...

After 2 months, finally some good news!

I swapped the front shock absorbers and by surprise that cured the shimmy problem. Absolutely no visible steering wheel shake anymore at 120kmh!

For who is interested in details:

Before I decided to change them, I had the old shocks tested at a test-bench in Germany. The passed the test without any doubt. I also did the traditional bounce test several times (push down the car by hand) and under such conditions, the shock apeared to do its work perfectly.

But despite these excellent test results, I wasn't very happy about how the car bounced on short speed-bumps at low speed and how it made the steering wheel shake really hard on some ridges at highwayspeeds. And because of this and also the never ending shimmy, I decided to swap them anyway.

While doing the swap, I compared the old and new shock. The only real difference was force required to push them inwards. Even though I found the new one not so difficult to push inwards, the old one required even less force. The rebound felt very similar. The old one also had plenty of gaspressure left inside. So at that moment I got a bit scared all my efforts would be for nothing (again)!

But I must say that small difference in force makes a huge difference on the road. The car now takes those short speedbumps very well and finally that shimmy has left the vehicle.

My conclusion is that the shocks of an e65 are very hard to diagnose, due to the pretty hard springs and the soft but "centered" shocks. With "centered" I mean that they stop about half way their stroke and you need a lot of pullforce to get the any further. This surpresses bouncing, even when they are really worn.

The car:
BMW 745i model 2002
Standard suspension (so non-sport)
No Dynamic Drive

I hope this post will help others to cure their "unsolvable" shimmy issue

Arjan,
That's good news. I'm glad to see that your issue has been resolved. Your resolution was totally different from mine but end result is that the damn vibration and shimmy is gone..Good luck and time to enjoy the ride.

Yes I am really happy with this achievement

This is not a common or expected solution for this kind of problem. But so far (approx. 150km) the car steers like a dream and I hope it stays like this!

BTW, I shot this movie to illustrate the difference between the old and new shock. As you can see the difference is there, but it is not very big. It is very difficult to tell if the new one requires 200% or just 25% more force to push inward.

thanks for the quick vid.