A four post ramp on load cells reads the weight on each corner, because the alignment bay needs it. One car reads seventy four kilos more than its documents say, all of it on the two offside cells, exactly where a person in the driver's seat would put it, with the doors shut and the seat empty.
I am the alignment technician at a tyre and exhaust place, and the ramp is mine.
How the ramp weighs a car.
Each post has a load cell and the display shows four corner weights and a total. It is there so that the alignment can be set with the car loaded the way it is driven, and it is calibrated with a certified weight every year, because a wrong corner weight means a wrong camber and a car that pulls.
An empty car weighs what its documents say, give or take fuel and a bag of shopping.
One car, a saloon that comes in for tyres twice a year, weighs seventy four kilos more than its book weight.
Empty. Boot checked, cabin checked, doors shut, nobody in it.
The extra is on the two offside corners, front and rear, split the way a person sitting in the driver's seat splits their weight between the axles.
I know the split because I have checked it. I sat in the driver's seat of an identical car and read the four cells before and after, and the difference is the same shape as the difference on this one.
Seventy four kilos, offside, seated.
What has been checked.
The cells. Calibrated, and the car put on the other alignment ramp in the next unit, which belongs to a different company. Same seventy four, same corners.
The car. There is nothing in it. I have had the seats out, because I thought somebody had put lead under the driver's seat as a joke, which is a thing that happens in this trade. Carpet, floor pan, wiring, nothing.
The wheels and the tyres, in case a wheel was ballasted. Same wheels as the nearside and they weigh the same on the bench.
The owner. He weighs about seventy four kilos. I have not asked him, but he is a man of average build and I have stood next to him, and when he sits in the car and I weigh it again it goes up by about seventy four more, so it is not him being weighed twice by some fault in the electronics. It is him and something the same size as him.
What the cells do during the alignment.
An alignment takes half an hour, and the display is live the whole time.
The seventy four kilos moves. Not much. It shifts between the front and rear offside cells by a few kilos, back and forth, at intervals, the way the corner weights shift when a person in the seat leans forward to look at something and sits back.
I have watched it do that with the car empty and the doors shut, from six feet away, for the length of an alignment, and on the third occasion I had the display recording and the trace is exactly the trace you get from a bored passenger.
What is done about it.
The alignment is set with the seventy four kilos on, because that is how the car sits and that is what the ramp reads and that is how it drives, and the owner says it drives beautifully.
I have not told him. He would want to know what it is and I do not know, and he is a nice man who has had that car since new.
What I do.
I do the tyres and the alignment.
The one thing I have changed is that I do not get into that car.
An alignment needs somebody to hold the steering straight, which means sitting in the driver's seat holding the wheel, and I used to do that myself.
I use the steering clamp now, which is a tool for exactly that, and the reason is the once, in the spring, when I got into the driver's seat to hold the wheel and the display, which my colleague was watching, went up by my weight on the offside cells, as it should.
It did not go up by my weight. It went up by my weight less seventy four kilos, and my colleague said so, and I sat in the seat, which was cold, in a way that was not the cold of a car that had been outside, and I have not sat in it since.