sam12345

iTrader: (1)

I don't have a vibration issue anymore but I was reading the miata forum and they mention shaving the tires to make them round. I thought this may help someone

The 65 MPH "Shimmy"

This is fairly common although it is usually corrected fairly easily.

First and foremost, be sure your tires are properly balanced. It must be done by a competent technician using a dynamic balancer. Some shops perform dynamic balancing, but they don't do it correctly. It should be done using a more sensitive setting and the technician should properly install the balancing weights. It should also be re-checked after weight installation. In addition, most major tire manufacturers put a marking on each new tire to indicate the "heavy spot" on the tire. Kevin Lakkis, field development engineer from Toyo Tire, notes:

Toyo measure uniformity – Radial Force Variation, Lateral Force Variation, Balance, etc. AND no tire leaves the factory beyond certain limits. (That is why Toyo has so few vibration complaints).

Every Toyo tire is marked at the low balance point with a yellow dot (it is not always a yellow dot with all tire manufacturers, but it is with Toyo). OE tires are also marked with a red dot, marking the low RFV spot (so they can be match-mounted with the rim).

A general rule is to match the yellow dot to the valve stem, however, many wheel manufacturers drill the valve stem hole at the light spot of the wheel.

In any case, when I mount my own tire, I spin up the wheel alone, mark the heavy spot, and match that to the yellow dot on the tire. In my limited experience, the heavy spot of the wheel is not always near the valve stem.

BTW, there is a new balance machine that puts a load roller wheel on the tire and actually measures RFV as well as balance. We are ordering one very soon. That type of machine should help with the 65mph shimmy. I plan to work with my local chapters with people who can’t seem to get rid of the vibration, and note exactly how sensitive the Miata is.

Check out this link: www.GSP9700.com

We (Toyo) have been using one of these machines for some time with excellent results.

We use it to diagnose vibration complaints.

There is a dealer locator which will help Miata owners find a tire dealer who has one of these special balancing machines. Since the GSP9700 is significantly more expensive than standard balance machines, it is safe to assume a tire dealer who owns one is an expert on diagnosing vibration problems.

Finally, if all else fails, take the tires to a specialist and have them "shaved" to 100% true. Manufacturing anomalies are not as uncommon as one would think. Shaving the tires will bring them back into the "round."

http://www.miata.net/garage/65_mph.html

mk2tmr2

iTrader: (1)

The Miata 65mph shimmy has nothing to do with tire roundness and has everything to do with the relative "floppy" nature of the convertible chassis.

That article has got to be ancient. It mentions road force balancing as a "new" technology. To be honest...the majority of the Garage section of M.net is ancient. Bear in mind the first gen Miata is pushing 26 years old.

sam12345

iTrader: (1)

My point is about shaving the tires round

mk2tmr2

iTrader: (1)

I think it's overkill and - having been extraordinarily active in the Miata community for over 5 years now - I can tell you that nobody who owns a Miata actually shaves their tires to rid of vibration. The only reason to shave tires is if they're brand new race or track tires that you don't have time to bed in before a track event.

A good road-force balancing job will rid your wheels of vibration. If you still have a vibration after having that done, the wheels and tires are not the culprit.

KsportUSA

Shaving tires is normally used with race vehicles.

as stated above, get your tires balanced, check bushings brake rotors etc also. Vibration should go away

sam12345

iTrader: (1)

Jeez, try and post something that may help and everyone is a critic

mitsuguy

iTrader: (2)

I'll add something - sometimes tires cannot be made right, period... no amount of shaving, balancing, road force matching etc - sometimes tires just have heavy spots that create a "thump"... (however, a road force machine will almost always pinpoint the exact cause) I've been using the Hunter GSP9700 since 2002. I've a little experience with it... The current model I have will even tell you if a tire is causing a pull... pretty good stuff...

only way to get rid of it - replace the tire...

all reputable manufacturers will warranty a tire for excessive road force within the first couple 32's...