It’s Spring Time!
Joking aside and yes, we know that is a pretty poor pun, but with an other harsh winter out of the way it really is “Spring” time. If we are to ever suffer a broken road spring on our car it is in fact likely that it will be at this time of the year. There is sound reasoning for this and one only has to look at the road surface post-winter to put two and two together. The cyclical freezing of water in small cracks in the road surface amplifies these little spaces into small puddles. Hidden under surface water we pound over these again without regard until we start to break up the edges and splash the detritus out onto the verge; QED a new pothole! It is probably the thundering blows of potholes and broken road surfaces that do the most damage to our road springs but it is not the only contributor.
Corrosion is always an issue when we add moisture to metal and our road springs are no different. They are made from high quality carbon steel, suitable for the “tempering” heat-treatment process imparts that springy character to the metal. Once formed, ends ground, heat treated and passed through all manufacturing quality controls the springs produced by Bilstein are powder coated in a special finishing process. This involves spraying electrically charged, dry, resin-based powder into the production tunnel which is attracted to the surface of the springs conveyed through here before being oven baked to activate the resin. What results is a homogeneous paint finish that is not diluted with any paint solvent and as a result adheres better and is less porous than traditional “wet” paint finishes. Quite a lot of effort you may think and you would be 100% correct.
Consider the duty cycle of the finished spring and you then realise just how hostile the working environment is. Cold, hot, damp, salty. These environmental conditions make for ideal corrosion circumstances so the only hope for the carbon steel is the powder coated finish as protection from the grit blasting and stone bullets that comprise the daily assault on the springs.
These production technologies work well and the springs last a long time in our cars despite the merciless pounding and chemical attack. Eventually a nick in the resin finish will kick off some corrosion but this in isolation is unlikely to cause issue. In fact if we look at the engineering of a spring and it’s fundamental operation we start to see how, why and possibly more interestingly where the spring will break. If we compare our road springs to the exotic torsion bar springs (a straight “rod” type spring which is loaded in torsion; a twisting force applied to one end relative to the other) of a formula one car we start to see the differences and then in fact the similarities!
A torsion bar spring is very simple with regard to calculations, manufacturing and operation but the comfort and flexibility we need in our road cars mean these are impractical. They would work if they were very long, a few metres long in fact but not so easy to fit in a modern saloon design but that is precisely what a coil spring is. Yes, a coil spring is in fact a torsion bar but wound into a helical shape which makes it very compact indeed. How, you ask can a linear force like we apply to our road spring become a twisting “torsion” force on the metal of the spring? Simple, we constrain the twisting action at each end of the spring and it becomes a long, soft and very robust torsion bar. The only issue is that there is along the length of the spring’s helix a portion at each end which is constrained (doesn’t move) and the balance of the spring which rotates due to the torque. This makes in effect a torsion bar with a lever at each end and it is these “levers” that break off the spring, just at the point where the highest stress exists.
In practice this is usually the last 1/2 to 3/4 turn of the helix at either end of the spring. In our experience it is usually this last piece of spring which will fatigue and break, the fatigue site may in fact originate from one of those stone chips in the paint.
In any case, if you have a broken spring then you are unlucky as it is a long sequence of things happening against the odds that cause this scenario. While you may think that it is only a small piece of spring that has broken then we would point out right away that the result is uneven pressure on each wheel on an axle, the only outcome will be compromised grip and extended braking distance. If you have a broken spring then don’t delay, get it replaced for the sake of safety. Ask for a Bilstein spring too, one with the highest quality carbon steel at it’s core and the most robust resin powder-coated finish to protect against failure.
Why not visit our web shop where you can look up your car’s road springs right from your registration or call in to any of our branches in Dublin (Tallaght or Airside, Swords), Cork or Galway? Try clicking on the Branch Locator button below.