[Josh] is replacing the springs in his car’s suspension. He wanted to know the travel rates of these springs, but apparently, this is a closely guarded trade secret in the industry. One company did manage to publish the spring rates, but they weren’t believable. Instead of taking this company’s word, [Josh] built a spring tester.
The theory behind a spring tester is pretty simple: apply a force to a spring, measure it, then measure how much the spring has traveled. Or compress a spring an inch or so, measure the force, and compress it some more. Either gets you the same data.
This spring tester is built around a Harbor Freight hydraulic press. Yes, the spring is completely captured and won’t fly out of the jig if you look at it wrong. The bottom of the press contains a few load cells, fed into an ATmega8, which displays a value on an LCD. For the displacement measurement, a ruler taped to the side of the press will suffice, but [Josh] used a Mitutoyo linear scale.
What were the results of these tests? You shouldn’t buy coils from Bilstein if these results are correct. The rates for these springs were off by 70%. Other springs fared better and won’t bind when going over bigger bumps. That’s great work, and an excellent application of Horror Fraught gear.


![This Herald is in much better condition than my 12/50 was. Philafrenzy [CC BY-SA 4.0]](https://hackaday.com/wp-content/uploads/2017/03/triumph_herald_southgate_london.jpg?w=300)



Of course, putting a car on the roof is a significant challenge, particularly when you only have the resources of a high-school student. Ensuring the roof was strong enough for a car, and then hiring a crane to do the deed, was beyond them. They therefore decided to take the wheels and outer body panels of a car and mount them on a wooden frame to give the appearance of a car.
