Diagnosing Wheel Vibrations

First, all of the mentioned parts/instructions can be found in your respective shop manual. If you do not have one and want to play with the car, make the investment! It goes without saying that investing some time to find a tire shop with good equipment is required..

These tips are not particular to our T/E/Ls - they apply to many cars. Last, I would point out that there is a lot of discussion on this matter in the archives, so I will be summarizing the salient points here.

Standard Disclaimer: Everything discussed here has been tried and has worked for me, but I am assuming that you are working with a competent shop. Shop around, talk with your mechanic or whatever it takes but find a good shop! Last, don't blame me when it breaks!! ;-)

Tire and wheel markings.

There are marks that the tire and wheel manufacturers use so as to align the "high" and "low" spot of the wheel/tire combo. (BTW, any good shop will know this)

The valve stem hole is drilled in the geometrically "low" spot of the rim (ie the smallest diameter, within manufacturing tolerances) by the wheel manufacturer. The tire manufacturer, in turn, marks on the wheel the radially stiffest part of the tire (which is effectively the "highest" spot) with a color spot or other label. Aligning these two, the spot and the valve stem hole, is called Match Mounting which is intended to give the smoothest ride possible.

Wheel Mounting.

Wheels can be aligned with the hub in two ways: either thru their lug nuts or via the hub-centric or center pilot of the wheel. Yes, that center hole in the back of your OEM aluminium wheel is what aligns the center of your wheel to the center of the hub. That is how our T/E/Ls are aligned if they have the OEM alloy wheels. This is important to note for our T/E/Ls, since the lug nuts just retain the wheels on the car, they do not align them.

Now, an aluminium wheel placed in contact with a steel hub will corrode galvanically over time, enlarging the pilot hole and misaligning the center of your wheels with the center of the hub the next time you dismount them. To check for this problem, dismount the wheels and measure the diameter of the pilot hole in various places and compare with the mounting flange diameter on the hub. Note: when my wheels were brand new, I always had to fight with them to remove them, they were so tightly mounted to the flange. To prevent the galvanic reaction just use a light coat of anti-seize or grease (just don't get any on the rotors - yes, it will not go onto the rotors if you just wipe a light coat on.) Note that a wheel that is only 0.006 in. off-center can cause an imbalance equivalent to 0.5 oz.

Vibrations while driving

As a rule of thumb: vibrations felt under 40mph are related to runout. Some people have mentioned bad vibrations after hitting big/deep/large/etc objects; this is definitely cause and effect in action. If a vibration is felt at over 40mph it is usually related to balance.

Other tips..

Still having vibrations? Try having your free runout, both in the lateral and radial sense measured. Both the tire and the rim should be measured for lateral and radial runout. The shop manual calls for 0.080 in., but a better rule is not to exceed 0.060in for the lateral and radial runout. If your runout exceeds this number, you will have perceptible vibrations! Note that runout is first measured on the car, and if it exceeds it, then the wheel should be measured off the car to isolate the problem. Yes, the bearings in the hub could also have damaged by that last pothole and causing vibrations too. It also can be that the mounting surface of the hub has been damaged or is defective, or that the stud circle of the wheel may not be centered on the hub. And finally, check your steering rack mounts too - worn/loose mounts can add vibration to your steering wheel.

Getting a good wheel/tire balancing job done..

Well, you are in luck, it is just that your wheel needs a balance job.. A good dynamic balancer should be checked so that it zero's itself before balancing the tire and after the weights are on the tire while the tire is on the machine.

But you say that your car still vibrates the cha-cha, there is one more thing to do: an on-car balance of the wheel, which will balance all rotating part on that corner. This is usually used for fine tuning a dynamic balance, and not everyone has the equipment to do it (some can't do it with the equipment..!). Note that if you rotate the tire, all balancing that you spent all that money for, is gone and will have to be redone.

Other rules of thumb are that if it takes more than three ounces to balance a tire, you will better off getting a different tire, ie, do not let anyone put more than 3 ounces of lead on your wheel. DO USE the right type of weights for alloy wheels -- they are usually dipped in a coating to prevent electrolytic corrosion of your wheels. Last, if you have a recent vibration - check to see that you did not loose a weight when you hit that pothole!

Need for accuracy

Most dynamic wheel balancers that shops use are accurate to 0.25 oz. (or about what a quarter weighs) -- this would generate a force of about half a pound at 65mph for a 24inch diameter tire. This accuracy used to be enough and the forces generated were not noticed in the days of rear wheel drive cars with long arm suspensions and parallelogram power-assisted steering. But on our cars, it would be totally unacceptable. There is a new "European" accuracy standard which call for an accuracy rate of plus or minus one gram ( that's 0.035 oz.!) Granted that this level of accuracy may be obsessive for the family van or the SUV, but for me, give me only perfection!

Some of the newest balancers can come close to this standard with an accuracy of 0.05 oz. - which is five times better than the balancer accurate to 0.25 oz. (which happens to be the same equipment previously used in the Indy 500...!).

Some of these newer balancers also allow for special modes so that the balance can be calculated with the weights on the inside; "patch balance" modes which allows for a weight "patch" to be mounted inside the tire when a lot of weight is needed to balance the tire (note that this is very specialized and hard to find machine); match mounting of the wheel and tire is supported on some machines; other allow for "split weight" modes so that two smaller weights can be used or when construction impeded mounting of a weight (note that this increases accuracy by eliminating the rounding error that sometimes occurs when a single large weight is used). Even the mounting of the wheel to the machine can be specialized with horizontal mounts, hydraulic collets, etc.

Other things to check

Things that do not affect the dynamic balance of your wheels are: tire alignment, warped rotors (they will make your pedal pulse when brakes are applied and simultaneously make your steering wheel vibrate back and forth for really bad ones - otherwise they do not affect the dynamic balance of the axle). Worn out ball joints, shocks, bushings, and tie rods can introduce vibrations that will feel like an out of balance condition.

Properly torquing down the wheels

Finally for those warping your rotors, skip the impact wrench and try mounting your wheels with a torque wrench using 70-80 ft-lbs of torque (the manual says 87 - 101 ft-lbs, but I have to make sure my wife can change the tire if needed plus I have never had a properly torqued lug come loose at these lower numbers). Even and equal torque on all lug nuts will prevent warping of rotors (with a possible exception being cross drilled rotors, but that discussion has been covered in the archives).