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Shimmy

My recently purchased 04 Miata has the famous 65mph shimmy, though it seems worst at 70-72mph. I bought the car anyway, just because it's so perfect in every other area I figured I could live with it if I had to.

I mentioned the problem to one of my co-workers who has a lot of muscle cars and the first thing he mentioned to me was if I had locking lug nuts, they should be lined up with the valve stem, since it is the lightest part of the wheel. I'm not sure how much heavier a small, thin patch of aluminum would be compared to a valve stem, but none of the lug nuts were lined up that way and I changed them. If it made a difference it was very small.

Next I came across this page

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whichsuggested getting the tires match balanced on a GSP9700, which is alsoable to detect if the tire is out of round. Using the dealer locator at
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I found a place a couple of miles from my house andhad them do a match balance, an alignment and rotate the tires. The techcame in and said one of the tires (Proxes R28 205/40r/17) had a bit of abump in it. He showed me which one it was and said that on a sensitive carlike mine I would probably notice it even though it wasn't really bad. By this time I had started to think the shimmy was just a natural frequency of the car or something. But the alignment and matched balance made a huge difference. There is still a shimmy but now it is barely detectable, maybe 10% of what it was.

The problem now is the tires. They only have 17k miles on them. I'm not sure whether to replace the one, replace them all, or what. The vibration really isn't that bad now, and as long as it doesn't return I can probably live with it for a while.

Anyway I just wanted to report that the matched balancing and alignment made a noticeable difference in reducing shimmy. The car is even closer to perfect than it was before.

Reply to
Carbon
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I had a 97 with the same problem - a shimmy at 67 to 72 MPH. It went away totally when I bought a set of Dunlop tires and had them properly balanced and checked for roundness - just like the group wisdom says!

Randy

Reply to
BCRandy

Dynamic spin balancing (on the car) should account for that as well as most other balance factors. Talk to your local racers to find the tire dealer they rely on.

"Only"? I've never gotten as much as 17k miles on a set of tires on my '95 Miata R.

-- Larry

Reply to
pltrgyst

That because you buy tires appropriate to the car. Not everyone does.

Reply to
Frank Berger

Are Proxes R28's inappropriate? They're what came with the car. I assumed they had lots of tread life left because the original owner didn't push them very hard.

Reply to
Carbon

Check around and see if anyone in your area can true the tire that has the bump. Not many places do, but it can make a huge difference if you can have it done.

Reply to
BAK

Shaving a used tire can correct some problems. A "bump" is more of a concern. It may indicate broken cords. If so, the tire may be unsafe at highway speeds. Safety at low speeds is also questionable.

That aside, checking new tires for excessive balance weight required, runout, roundness, and visible tread pattern wobble is needed if the "shimmy" is to be avoided. My experience over many years is that about one of five replacement tires fails one or more of the above tests.

Reply to
Chuck

Don't know the R28. Is that OEM? The OEM Bridgestones that came with my '96 had dangerously low traction in the rain. I was literally afraid to drive until I learned a bit about tires. At that time I replaced them with Dunlop all season tires which were OK and got good mileage, but since then have hae Toyo T1-S and T1R. These are high performance summer tires with outstanding traction on dry or wet roads. But useless on snow. The softer compound used give these tires much lower treadware than all-seasons (I get

15-20K). Expensive but a lot more fun than all-seasons. Yokahama AVS 100 is a reasonable alternative.
Reply to
Frank Berger

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