A wheel balancer spins the wheel, reads where the heavy spot is, and tells you where to put a weight. Take the weights off any wheel and it reads out of balance, because the weights were the balance. This one reads zero with its weights on the bench, and the balancer's log shows it has been spun in the night.
I am a tyre fitter and the balancer is the machine I use most.
How it works.
You mount the wheel on the shaft, pull the guard down, and it spins up and reads the imbalance on two planes, inside and outside, in grams and at an angle. You stick or clip weights where it says and spin again, and a good wheel reads zero, zero.
Every wheel needs weights. Tyres and rims are never perfect. A wheel with the weights removed reads whatever it read before they went on, which is usually twenty or thirty grams somewhere.
The balancer logs each spin with the result, because the boss likes to know how many wheels we do.
One wheel, on a car that comes in every year for a pair of tyres, reads zero with its weights off.
I noticed because the weights had fallen off, both of them, which happens on old rims, and I spun it before fitting new ones to find the spot.
Zero, zero.
A wheel with no weights that reads zero is a wheel that does not need any, which does not happen, and if it happened once you would not remember it. This wheel does it every year, on every tyre I put on it.
New tyre, different make, different batch. Mounted, spun, zero. Weights off the bench.
What has been checked.
The balancer. Calibrated with the reference wheel it came with, which reads what it should. The other three wheels off the same car read the normal amounts and get their weights.
The rim. Weighed in sections on a bench scale, which is a thing I did on a slow afternoon, and it is heavier on one side, the way a rim is, by about the amount that should need thirty grams of weight to correct.
Another balancer. The truck place next door has a bigger one. Zero, zero.
So the rim is out of balance on the scales and in balance on the spin, and it is the spin that is real, because the spin is what the road does.
The log.
The balancer logs each spin and the log has time stamps, and I looked at it because the boss asked for the monthly count and it was high.
That wheel had been spun eleven times in a month. Four were mine. The other seven were between two and three in the morning, on nights the workshop was locked with the wheel, on that car, in the compound outside, not on the balancer.
The results logged for the night spins are not zero. They are thirty grams at a hundred and ten degrees, inside plane, which is the reading I would expect from that rim by the scales, and which it has never once given me.
What that means, as far as I can take it.
Something spins that wheel on my balancer at night and reads the imbalance that is really there, and by the morning the wheel is on the car in the compound, and when I spin it, it is gone. As though it has been corrected, in the night, with a weight I cannot see, at the place the machine said.
I have run a magnet round the inside of the rim. I have felt round it with my fingers. I have painted the inside with marker and spun it to see whether anything scuffs. Nothing is on that rim but the rim.
What is done about it.
The car goes out with four balanced wheels, one of them with no weights on it, and it does not vibrate, and the customer is happy, and the tyres wear evenly, which they would not if the wheel were out.
I tell nobody, because the sentence is a wheel that balances itself and I work with men who would enjoy that too much.
What I do.
I fit tyres.
The one thing I have changed is that the balancer's guard stays down when I leave, and I unplug it at the wall.
The night spins are still in the log. Seven or eight a month, on a machine with no power to it, and the result is always thirty at a hundred and ten, and on one of them, in the spring, the log also shows the guard being lifted and lowered, which the machine records because it will not spin with it up, and the guard was down when I came in, and warm, at the handle, at seven in the morning.