Shimmy at 70 mph....

[kqw]

Getting a shimmy at 70 mph. solid up to 70 mph and if I go over 80 mph, it smooths out....

I'm thinking wheel balancing???

Thanks in advance

[SandyI]

I don't get it. You only have the shimmy from 70 to 80?

[kqw]

Yes, Once I hit 70 mph it shimmy's a bit then smooths out the faster I go.

[sammyg2]

It is either tire balance or tire out-of-round. My guess is balance.
Suspension systems are designed to dampen movement to a in a certain range of frequencies.
If the imbalance is excited at a given frequency (speed of rotation in this case) it can transistion into a frequency that is not well dampened or is at a severity that it overcomes that dampening.

[kqw]

Thanks, I though balancing also. thanks or the confirmation.

[Zeke]

As Sam says, tire balance is something that comes in and out at different speeds. I have the same thing and I'm arguing with the balance guy right now. He doesn't have time to take my car to the nearest smooth road which is miles away. But, it's there. Get them reabalanced and check for round while you're at it.

[Venetian]

I had a very similar problem. A new set of tires solved it.

[kqw]

Tires are only 4k miles from new. I'll have them re-balanced...

Thanks again

[Tommy B]

i have the same problem. i wonder if i bounced a weight off the wheel with our crappy NYC roads

[kqw]

Believe it or not, the situation just started. a few days ago when I was traveling the WONDERFUL streets in Philadelphia......Tommy B that makes a lot of sense.....

[Decolliber]

I had the same problem with some new RUF wheels and P-Zeros. Slight vibration at 60-65mph. I had the wheels rebalanced and no help. Then I rotated the front wheels on the studs, 180 degrees from the original position, and the shimmy has almost gone.

[kqw]

My studs were marked at the factory, I.E., which stud to corresponds with the wheel locks and valve stem positions. I just think I either lost a weight or the tires have settled in and need re-balancing.

Your thoughts...

[1973911s]

I had this problem last week, was between 60 and 80. Rebalanced the front and all gone.

Michael

[sammyg2]

I have a vibration in the front end of my car but it isn't all due to balance.
Something about an over-aggressive driver flat-spotting the fronts at the last AX
Funny thing is, it comes and goes. I figure that if both flat spots are 180 degrees apart the steering wheel shakes, if they are out of sequence I don't feel it. All it takes is one wheel to turn a little faster than the other (like going around a corner) makes the shake either come or go. It isn't very pronounced but I know it's there.
I'm just going to ignore it until the tires wear down enough to justify replacement.

[Par911]

Originally posted by kqw
Believe it or not, the situation just started. a few days ago when I was traveling the WONDERFUL streets in Philadelphia......Tommy B that makes a lot of sense.....

Funny, I just got back from a trip to NE Philly, Cottman and Castor Ave. After hitting some nasty potholes on I-95 and Philly streets, I now have the same situation you are describing. I just spent $350.00 at a local p-car shop to get the alignment done after replacing the steering rack and lowering the ride height .

[Zeke]

Originally posted by Decolliber
.........Then I rotated the front wheels on the studs, 180 degrees from the original position, and the shimmy has almost gone.

Pretty smart move. Goes to show you why final trimming of a complete balance job has to be done on the car with a strobe or other device (there is another kind of moveable weight that clamps inside the wheel lip if you have one).

[john70t]

A couple of tricks are to chaulk the tire and spin it to see if it ends up at the same place every time.

Also, put a dial indicator (with the roller end) on the rim and each part of the tire for out-of-roundness. The tire can be rotated on the rim and then re-balanced, sometimes, to correct natural imperfections in the manufacting process, or it can be put on special machines that puts pressure on it and shaved to eveness.

[Nine9six]

The only problem with checking tire out-of-round, is you must know the spec. tolerance from the tire mfg. Even then, you can get a tire that meets mfg. standards, but still needs additional attention, and rebalancing.
Speaking from a motorcycle world, I know that race teams precheck their tires on a "STANDARD" (a wheel that is known to run true in all axis), prior to accepting the tires from the vendor. Race tires, which are constructed under stricter mfg. standards, still see tires that are out-of-round.
Just my $.02, (whether my brother likes it or not)

[Zeke]

To the last 2 posts: Once optimizing out-of-round and weight variables between rim and new tire, It might still be necessary to shave the tire on the rim before attempting to balance. If the rim is slightly out, the tire can be made to sit on the rim in-round. It will be useless in any other postition on that rim or any other wheel once this is done.

It has been said that 1/16th OOR will produce (depending on tire size) around 400 lbs of weight imbalance at 100MPH. Perfectly balanced wheels are much kinder to shocks, the car in general and will travel more miles before needing replacement even if rubber is removed in the beginning to get them round. The will follow the road surface better giving the most traction available for the particular tire/rim combo.

[kqw]

PAR911..

I know you are pissed.....