Reinforced steering parts – a good idea?
Several of the steering parts suppliers on the independent aftermarket have gradually built up a programme of reinforced steering parts. These alternatives are developed when it turns out that the lifetime of the original design does not meet expectations. At first glance, this sounds like good idea, but is it that simple - and what are our thoughts on this subject?
To properly shine light on this topic, it is important to understand the development process of a steering part. Steering parts are part of a complex system, that besides the steering system also includes wheel suspensions and transmission parts. The dimensioning of the individual steering part - both physical dimensions and choice of material - is based on the loads which the part is expected to be exposed to as part of the steering system as well as the wheel suspension and transmission. The part is designed as a 3D CAD model, which is subsequently exposed to FEM (Finite Element Method) calculations / simulation, thereby ensuring that the dimensioning is correct. This method is first used for all individual parts, but thereafter also for the connected system as a whole. With this procedure you get as close to the real world as possible. And at the same time, it is ensured that the probability of the individual parts passing the subsequent physical tests is as high as possible.
It is therefore unavoidable that when changing one part's physical dimensioning, the dimensioning of the overall system is altered as well. Forces and vibrations that over time may be damaging to a single component are, now that this component is reinforced, most likely deposited elsewhere. As parts for the steering system and wheel suspension belong to the category of safety components, it only makes sense to ask yourself the following question: Has the very comprehensive and costly work of testing whether the change of design effects other components of the system been done, and is there any documentation of this?
It would be very interesting to find out how good the reinforced parts actually are. Is there any difference? How much better are they? We have not been able to find any independent documentation answering these questions, which, of course, also is a very comprehensive and almost impossible task.
In an effort to find getting closer to answering these questions, we have - based on two references, which on the aftermarket are offered in a specially enhanced version from several suppliers - made comparative tests between OES, reinforced, standard and Triscan parts on a large number of parameters. We tested the following two stabilizer rods for PSA and VAG.
|OES||5057* (50, 57, 62, 64, 77)||6Q0 411 315* (A, C, D, F, G, J, L, M, N, P)|
|Triscan||8500 28624||8500 29617|
We have tested the two stabilizers on a wide range of factors. Below we illustrate the most important factors relating to durability.
Axial clearence diff: Is the backlash we have been able to measure after the stabilizers have been exposed to 100,000 cyclic tests with 200 kg. at 5Hz. As can be seen, all stabilizers live up to what must be characterized as an acceptable level relative to the OES part. The reinforced part and our latest part are completely identical.
Sealing: All parts except one of our competitors' standard parts passed the density test, which is divided into two. During the first part of the test, a leak test is performed at 1 bar on the stabilizer rubber sleeve. Subsequently, a leak test is performed at 3 bar on the cap, which is either made of metal or plastic.
Surface treatment/Corrosion resistance: As can be seen, the OES part and the reinforced part of our competitors do not provide as good corrosion protection as the other two parts. The less effective surface treatment is a Cr3 + chromating that provides 240 hours of protection in a salt chamber test. The more effective surface treatment, which is obtained by carrying out a cataphoretic (electro-coating) lacquering process where the item is immersed in an epoxy-based paint, provides 720 hours of protection in a salt chamber test.
We have made up our mind
At Triscan we have made a choice. We do not want to offer a separate programme of reinforced parts - for several reasons.
1. Steering and wheel suspension parts belong to the safety parts category.
2. We believe it is difficult - not to say impossible - for others than the car manufacturers to calculate and test the consequences of changing physical dimensions.
3. We have several examples of how we, in cooperation with our manufacturers, successfully have improved a part, without changing the physical dimensions of said part.
4. We have several examples of how we, with a standard product and without extra cost, can achieve the same durability as a reinforced and more expensive product.
5. It is much easier for all parties to relate to one rather than two different alternatives.
We have made our decision - and hope that, based on this article, it is now easier for you to make yours.