How to Choose a Rod End (Heim Joint)
What's the difference between these three rod ends?
Yes, one is female and two are male, but that's not the most important difference. Turns out they're all made of very different materials and they therefore have very different properties and applications. From left to right, they're made of chrome moly, plated steel with plated steel. Other typical materials for rod ends, but not pictured above, are stainless steel and aluminum.
There's also a difference between these three that you can't really see: the inside of the housing that contains the spherical ball has different coatings. This is called the bearing race and there are a few difference options available. The leftmost is coated in PTFE (Teflon, a trademark of Dupont), the middle in bronze and the right one has not coating, meaning the steel housing acts as the race.
So they're different great what's the point? Well, the differences are certainly not for vanity and when buying rod ends it's important to choose the right one for your application. Here's our guide to help you figure it out.
Rod End, Heim Joint or Rose Joint?
All three names mean the same thing and the difference is all just cultural and historical. The Germans came up spherical rod end bearings (the most proper and technical name for these) in the 1930's. Once the Allies got the technology via an aircraft that was shot down, supposedly in the Spanish Civil War in 1930's, the exclusive patent was given to the H.G. Heim Company in the US and Rose Bearings Ltd. in the UK. That's how the alternative names came about.
So now that we've done our history lesson, here's the real info about the different varieties of rod ends.
Steel Rod Ends
This is the most common rod end in use, largely for commercial non-automotive applications. It provides a great value for many applications where the added expense of a higher-end rod end is not necessary. The race is direct steel on steel, which can lead to shorter wear cycles, but of course is cheaper to produce. These are not recommended for automotive applications and we recommend staying away from manufacturers who provide these in their kits for suspension components.
You can browse for steel rod ends by clicking here.
Steel PTFE Rod Ends
This is a steel rod where the inside of the housing has been coated in PTFE to create a smoother surface with the coated ball. This is the most common commercial-grade rod end, since it has greater durability than a steel-raced (steel on steel) rod end and the motion of the ball is much smoother.
This rod end style can also be used for some automotive applications. For example, when constructing end links for a car this is a sufficient rod end, but it should not be used in higher load application applications such as control arms. There are also certain situations when a designer prefers to have the rod end be the first failure point in a crash instead of the chassis and thus choosing this slightly weaker rod end over a strong chrome moly is appropriate.
You can browse for steel PTFE rod ends by clicking here.
The rod end of choice for motorsports applications is one where the housing is made of chrome moly. Whenever someone talks about race grade or aircraft grade, this is what they mean. Unfortunately, aircraft grade doesn't really mean it's used on airpcraft. It turns out that this style of rod end is actually typically not used on airplanes because it's too big. It simply means the quality is extremely high, i.e. good enough to theoretically be used on aircraft if it fit.
You can also see in the picture below, that the chrome moly rod end has a much thicker eyelet vs. the standard steel one. It's built to withstand much higher loads.
You can browse for chrome moly rod ends by clicking here.
High Strength Stainless Steel
This can also be used in motorsports applications. In general, unless stainless is absolutely required, chrome moly is the best options for a race-grade motorsports rod end.
You can browse for high strength stainless steel rod ends by clicking here.
Typically also a commercial-grade rod end for use in applications where corrosion-resistance is important.
You can browse for stainless steel rod ends by clicking here.
Last but not least, aluminum rod ends are also available. They are of course somewhat lighter, but their biggest disadvantage is that their rated load for shear is much lower than steel. Especially in suspensions, this type of load across the rod end is common and they therefore should not be deployed in the running gear on cars.
You can browse for aluminum rod ends by clicking here.
This Tech Tip is courtesy of Tim Trampedach, an SL-C builder with an all-Porsche drivetrain. You can see the original version on his Level X Motorsports site at this link