A comprehensive maintenance program should be a part of any racing operation, and that means you’ll be replacing worn parts on a regular basis. One item that should never be overlooked when you’re inspecting a racecar are the rod ends, but if they need replaced do you know what material to choose for new parts?
To help set the tone for what to know, John McCrory from Aurora Bearing Company breaks down the basics of rod end materials.
“The materials used to manufacture rod end bodies used on racecars basically fall into four categories: Low Carbon steel, Alloy steel, Stainless steel, and Aluminum. I’d like to define critical and non-critical: on a vehicle that accelerates from rest to up to 200-plus mph, virtually every rod end used is critical to some degree. For this, I’ll use critical to pieces that attach the wheels to the car or control/define its movement.”
If you’re dealing with an application that is non-critical and doesn’t see a heavy load, a rod end made of Low Carbon steel will work. This includes things like door hinges, wing or spoiler mounts, and throttle linkages. The Low Carbon steel can be used in suspension applications, but great care must be taken with this.
“Why do the front mounts on ladder bars have a “strap” surrounding the rod end? Because a low carbon rod end that is often used in low-price-point ladder bars can bend or even fail under load. These rod ends are bending under load, and the strap keeps the amount of bend to a minimum. However, continual bending, even a small amount, can result in fatigue failure in the threaded rod end shank. On a low power, lightweight, traction-limited car, low carbon rod ends on the front of a ladder bar can work. As all those factors increase, such a part becomes increasingly marginal,” McCrory says.
Looking at the big picture, you really want to use rod ends made of the strongest material possible for critical parts. The rod ends that are used on the suspension of your racecar should be made of Alloy Steel, or more commonly known as chrome-moly. McCrory explains why you want rod ends that are made of this strong and durable material.
“Alloy Steel has a much higher load capacity than equivalent size low carbon joints. While they admittedly cost more, the increased reliability more than justifies the cost differential. On a high horsepower four-link car, this includes not just the four-link, but the locator device, as well. Keep in mind that while the front of the car does not see the violent loads of a launch, at the top end they are relied upon to keep the wheels pointing where they should on sometimes hard deceleration.”
Stainless Steel might seem like a good choice, but you need to see if the material used is high strength or low strength. Many are attracted to Stainless Steel because it can be polished to a shiny finish and resist corrosion, but that doesn’t make it the best overall choice for a critical part application.
“For critical applications, as noted with alloy steel parts, you should stick to high-strength parts. Historically, there have been some excellent high-strength stainless steel rod ends used in suspensions. Some of the first high-end aerospace-derived rod ends available to the racing community used heat-treated 17-4Ph body rod ends. These parts developed an excellent reputation, however, it should be noted that a good 17-4 stainless rod end is good because of who manufactured it, not because it’s stainless. Yes, that statement can hold true with any material, however, the first 17-4 motorsports rod ends were made by manufacturers who also made military and aviation rod ends, to sophisticated specifications,” McCrory says.
Rod ends that use aluminum as a base material can be used in a racecar, but they shouldn’t be used where a high load will be placed on them, as these will have a load capacity similar to a Low Carbon steel rod end.
“While strong in the T6 heat-treated condition, 7075 has poor elongation properties. It’s not forgiving, and it doesn’t give or bend at high stress. They may look comparable to low carbon joints when evaluated on load capacity alone, however, you would be hard-pressed to find them on the rear suspension of any door-car in critical locations, and they are rare or not common on the front,” McCrory explains.
So when it comes time to do maintenance to your racecar and you need to replace rod ends make sure the material is correct. The cheapest or most attractive-looking product might not be the best for your application and this could lead to issues. Just like so many other parts on a racecar, it’s best to put strength as the priority of the part to make sure your vehicle performs its best.