Experience in despair workshops. Everything checked a hundred times, even if tuned markings on tyre and rim are correctly assigned. Balanced to within 5 grams, of course, and yet at certain speeds certain vibrations can be felt at all and in the steering wheel.

Even the workshop foreman is slowly at a loss, already thinking about changing tyres and/or rims. One would have to whisper to him that you may have overlooked a phenomenon, which is somewhat addressed by the picture above. Because balancing is the elimination of mass inequalities, but has nothing to do with geometric ones. And actually, you would have to worry about at first.

Our picture above does not quite reflect this. This is about the measurement of rims alone, probably those that have some sigificant irregularities. No, we are looking for manufacturing tolerances, separately for tyre and rim in mounted condition.

How to do that? Quite simply as shown above, just place the dial gauge from the outside on the centre of the part of the rim where the bead of the tyre is located on the other side, i.e. exactly at the connection between rim and tyre. Instead of the dial gauge we take a pencil or some chalk and while turning it on an (old) balancing machine we bring it closer and closer to the rim.

At some point there are lines on this one. If we do the same with the centre of the tyre tread, we will get one spot each where the tyre deviates furthest outwards and the rim inwards (picture above). If tyre and rim have no defects on the outside, the tyre should be mounted on the rim in such a way that the two markings are on top of each other.

However, if the error is not eliminated after careful re-balancing, then the procedure would have to be repeated with a dial gauge as indicated above, comparing the values with valid tolerances. Thus, unless otherwise specified by the manufacturer, the tolerances are 1.5 mm for the whole wheel, 1 mm for the steel rim and 0.5 mm for the aluminium wheel.

Once you have used the dial gauge with hopefully a very secure stand, you can do this for the tyre flank. The measurement is taken in the middle of the tyre side and then on the rim flange. Please always pay attention to what the valve of the tyre does with your measuring device, if necessary turn the wheel the other way round from there. If there is a bigger difference, mount the tyre carefully once again.

After such careful measurements we can exclude the possibility of exchanging parts because of geometrical problems. If complications persist, the only thing that remains is to balance the wheel on the vehicle. It has very special demands on a vibration-resistant workshop floor. Also, the car may only be lifted with the jack on the outside of the wheel suspension, not with the lifting platform.

It is of no use to get a good result with the suspension deflected and during the test drive everything is back to the old. Special regulations apply to wheels on the drive axles. Here the dismantling of the drive shaft may be required. Before you drive a defect into the car with the balancer, you should check here.

In any case, other rotating parts are also tested here, e.g. the brake disks. Of course, you have long since assumed clean rims and their contact surfaces. Also play in the wheel bearing is part of it. Finally, as a desperate act before the complete replacement, the wheel can be mounted offset by certain turns.

By the way, you cannot always rely on the dots on the tyre, for example. Usually the red dot is the lightest part of the tyre and belongs to the tyre valve. But there are manufacturers, this is the lightest point due to a yellow dot is marked and the red dot indicates the one with the greatest deviation from concentricity to the outside. ReifenDirekt.de even says that manufacturers' factories are marked with it.

After the corrections described above, these markings have no further meaning. By the way, in automatic optimisation machines, wheels are almost unnoticed scanned by laser scanners. After such measurements, they indicate a position in which the tyre and rim harmonise better with each other. Of course, this includes a warning if the tyre and/or rim is out of tolerance fall.