Blog tripod vs. Rzeppa joint

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In this blog, we would like to talk about the difference between the regular, ball-type CV-joints used in most passenger cars and the tripod joints that we use in our driveshafts. First of all, there is a general misconception about the term CV-joint, as the tripod joint is in fact a CV-joint as well. The CV abbreviation stands for constant velocity.

The function of a constant velocity joint is to transmit power, while the angle between the input and output can vary. The constant velocity part means that the rotational speed of the assembly does not change regardless of the angle of the joint. This is the main difference when compared to the universal joints used before the CV joint was invented.

The universal joint was compact, but the output did not have the same constant velocity as the input. This difference in velocity gets larger when the angle gets greater. The joints generally allow some axial movement, as the total length of the driveshaft will change when the suspension goes up and down in its motion.

Figure 1: A traditional universal joint

The outer race is attached to the output, while the inner race is attached to the input. If the input turns, the inner race will press the balls against the outer race and therefore the joint will rotate. Due to the shape of the inner and outer race, the joint can also be at an angle while still remaining the same rotational velocity. There are variation of this joint that allow for axial movement, also called plunging. This can be achieved by either having an outer race with longer grooves (double offset joint) or having the grooves in the inner and outer race not parallel to the shaft, but at an angle and therefore creating more length (cross groove).

Figure 3: Rzeppa joint assembly

Figure 4: Parts in a tripod joint

Tripod Joint

The tripod joint does not work with six balls to transmit the rotation from the input to the output. Instead, it uses three rollers on a spider. This spider replaces the inner race. The rollers have needle bearings inside and therefore rotate very freely.

This spider fits inside a cup with three matching grooves, which is usually integrated with a flange or shaft like the Rzeppa joint. This groove allows the joint to operate at an angle, but it also allows axial movement in the joint without sacrificing drive. The plunge can easily be made longer or shorter by changing the design of the cup, while the rest of the parts can remain the same. The rotation is transmitted in the same way as the Rzeppa joint; the spider presses against the rollers and the rollers press against the body of the cup.

Figure 5: A Tripod Joint Assembly

Choosing the right joint

There are a few benefits to each style of CV joint. The main benefit of the Rzeppa joint is the larger articulation angle they provide. For this reason, most cars use this type of joint on the wheel side of the driveshaft. This is especially important in front wheel drive cars, where the CV joints copes with both the steering and suspension movement. The tripod style joint allows for less angle, but more axial movement. Quite often, a tripod style joint or a plunging Rzeppa style joint is used on the inboard side of a car. This means the driveshaft as a system has a big allowance for both changes in angle and length. In case two Rzeppa joints or two tripod joints are used, one end is usually axially fixed while the other end allows for axial movement. This can differ between different designs.

Street and rally cars
In street cars, the tripod joint is mostly used because they have plunging movement, are easier to make than a Rzeppa joint and most of the time have sufficient range of angle on the inboard side. The required angle determines whether a tripod joint can be used. This is also dependant on the suspension geometry and the suspension travel. A car used in rally racing could for instance have to much suspension travel, making the angle on the joint too big. Consequently the amount of camber in race cars also plays a big role in the required angle on the joint. These angles and the geometry can be measured using one of our measurement shafts.

Race cars
For race cars, there are other benefits to the tripod joint. The tripod joint is more compact than the Rzeppa joint. The result is that a tripod joint of the same size as a Rzeppa joint is stronger or a tripod joint with the same strength as the Rzeppa joint is smaller and lighter. Sometimes, when space is at a premium, switching to a tripod joint means a stronger driveshaft can be made without using more space.

As the suspension of the car is constantly moving, the joint is constantly moving as well. The tripod joint creates less friction during movement, as the rollers have needle bearings inside them. This also means they create less heat. If a car is raced, this could make the difference between the grease inside the joint being functional or not. This helps a lot with the longevity of the joint.

Another benefit of the tripod style joint is serviceability. The joint can be completely taken apart and serviced, whereas the Rzeppa joint is usually a replacement item. This also means that the tripod joint will last longer and that it’s condition of can be examined in between races, which reduces the chance to drop out of a race due to driveshaft failure.

Regardless of what type of joint is chosen, they all have to be sealed. This prevents moisture or debris coming in from the outside and it keeps the grease inside the joint. This is usually done with a rubber or silicone boot.

Conclusion

In conclusion, both types of CV joints mentioned here have their own benefits. As race cars are mostly rear wheel drive and have limited suspension travel, the tripod style joint can be used. This provides many benefits over the usual Rzeppa joint, most importantly that they are stronger and easily serviceable.

Pro’s and con’s of a Tripod joint?

• Easily customizable
• More compact and stronger
• Less friction and heat
• Serviceable
• Smaller articulation angle

Pro’s and con’s of a Rzeppa joint?

• Big articulation angle
• Not serviceable
• Complex to produce

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