Topic: Vibration w/ new Wheels/Tires

[mis3]

A new set of tires/wheels was installed by my local dealership a few days ago. On the highway, I noticed a slight vibration with my steeling wheel at 120 KMH. This vibration would go away after 130 KMH go the way to 180 KMH. I did not drive pass 180 KMH.

Talked to the dealership, they said they would balance them again at my next visit. Is this strickly a wheel balancing issue?

[davidm]

Usually it is just balancing with this kind of problem.

[morty]

Make sure the wheels are hub-centric. If not make sure the dealer has installed hub-centring rings. Very prominent on vehicles using lug bolts. If the wheel is not centered on the hub you will get vibration whether they are balanced or not.




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[mis3]

I can understand if the vibration increases as the speed goes up.

In my case, vibration occurs only between 120-130 KMH and it goes away at speed over 130 KMH.

[davidm]

The same problem happens on the Miata (known as the 65 mph shimmy = 104 kph shimmy).  Seems to have to do with the vibrations of the out of balance tires hitting a certain frequency that resonates with the car (my hand-wavey non-tech explanation).  Shimmy disappears by about 110kph.  Miatas are very balance sensitive and this is usually fixed by a really good balance job.

Sorry Mort, I always forget about the hubcentric thing ('cause I always buy OEM wheels or stuff from you).

[tpl]

Yes its a resonance effect.
unbalanced tire(s)
out of round wheel/tire combo  
round but off centre ( the hub ring thing)
Particular tire tread pattern resonating itself or with the suspension ( BMWs suffer from this)
any of the above on a specific road surface.

The whole tire ( sidewall) + treadpattern + road surface + spring rate + rotating mass + non rotating mass + damping resonant frequencies in the shock absorbers+ bushings+ antiroll bars  forms a mechanical "tuned circuit" or rather many, many  of them... think of it as a set of VERY BIG organ pipes in a VERY big hall.

most of the time all of these just produce a mechanical "white noise" but sometimes you get an actual "note" and thats what you feel.

In the old physics books it would be shown as a weight hanging from a spring with a "shock absorber" across the spring and then there would be a page of equations to show what happens to the system when you apply a force.

A modern car suspension probably has many thousands of combinations.

My bmw 330xi with its all wheel drive hardware adding more rotating mass has resonances that feel like a bad imbalance at various speeds with some road surfaces with its Yoko AVS sport tires...but on other roads at the same speeds  it is totally smooth.
DavidM's 328 might have the same problem with those tires but it undoubtedly would happen under different circumstances at his car is lighter than mine with a slightly different suspension set up. cars with indepenet rear suspension can sometime feel as if its a bad front tire as well... depends on all the same factors but usually somewhat less  

The short sidewalls of modern car tires has pushed some of the resonances up in frequency which is good for vibration but bad for tire noise

Mort here is a question for you. Do the runflat tires on more and more new cars sound different form an equiv size in a non-runflat?   My guess it that they would because of the construction.

[morty]

Sound is of course dependent upon the person listening. The run flat tires definitely have different construction, which includes a very stiff bead package and sidewall to support the weight of the vehicle without air. Dont tend to hear many complaints, which is surprising since they come on many high end cars. This tells me that it is not a problem. Low profile tires are definitely less forgiving and capable of absorbing vibration problems. If the vehicle has problems with component wear it is more likely to show up in lower profile tires.




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