Question about Rod Ends

[Caito]

Hello guys, I'm having some doubts about rod ends.

There are basically two things I don't understand.

What's the difference between a "classical" rod end



And this type of rod end




I know both are used in racing suspension cars. But I don't know where resides the difference in both, how they support forces maybe.


The other doubt is, when using the first rod end in a double A-arm type suspension the rods that are connected to the chassis are sometimes vertical and sometimes horizontal.

I went with the builder of TRV6 cars ( a category in Argentina) and I've seem he uses the second type rod in the tip (sorry, don't know the word in english) and the first type to connect the arm to the chassis. He uses the last two in a way that is parallel to the floor, and I've seen in many pictures of other racing cars that are perpendicular to the floor.

Is there any advantage in using any of them?

Maybe my problem is that I don't understand fully the forces on a suspension arm.


Thank you very much in advance,


Diego Andrés

[Scuderia_Russ]

As far as I know 'Rod End' is a brand name that similar to Hoover and Tannoy has overtaken the use of spherical bearing. Personally I call the first a Rod End and the latter a spherical bearing.

I'm no engineer so I can't talk about what forces are exerted on the joints at this point or what differences their positioning makes but by attaching wishbones to the chassis using them castor angles in particular (less so camber) can be adjusted by winding the rod ends in or out depending what you were trying to achieve.

The spherical bearings shown in your pic can be found in all sorts of things. Damper eyes, wishbones (usually the outer end supporting the upright), inside a mounting that holds a gear linkage for example. They are usually held in with snap rings or circlips and I can vouch for them sometimes being a bugger to press out to replace!

[Jersey Tom]

Rod ends are indeed the first, and sphericals are the second.

Rod ends are designed to be loaded in tension and compression only. As such, they work well in tie-rods, push-rods, and on the chassis-side ends of A-arms. Since they're threaded, they're easy to replace.

Where one can run into trouble with rod end bearings are when you try to put them at a location like the "tip" of the A-arm (the wheel-side mount point). The threaded shank is then loaded both axially and in bending. You can get away with it, but you have to generally use a larger and heavier rod end to support the additional load. A spherical bearing on the other hand, without a threaded shank, works well for taking loads in multiple directions. They're a little more pain in the ass to replace, and when you press them into a housing there's the potential for binding them up a bit.

You can use a spherical any place you can use a rod-end, but you can't always use a rod-end where you can use a spherical.

Regarding the orientation of all these bearings, anything works really. Packaging constraints sometimes lead to one versus another. The difference is in what takes up the misalignment. Orienting them vertically in an a-arm, it's rotating inside the actual ball. Horizontally, the ball has to rotate within the housing. Former may have less friction, I'm not sure.

[Caito]

Thank you very much, it's now very clear

Finally, when you choose a rod-end you have to make sure the threaded shank is working as it's suposed to be. (direction wise)

The rod-end could be considered as a spherical with a piece of thread :p (sorry for this haha)

Just one last doubt that arised. Are the spherical bearings effective when you load them in the direction mm.. how can I say it "of the hole".

What I mean is, not applying a force to the wall of the bearing. Applying it "perpendicular to the wall".


Thanks once again.


PS Excuse my english, it's not my native language.

[Belatti]

The rod-end could be considered as a spherical with a piece of thread :p (sorry for this haha)

Just one last doubt that arised. Are the spherical bearings effective when you load them in the direction mm.. how can I say it "of the hole".

What I mean is, not applying a force to the wall of the bearing. Applying it "perpendicular to the wall".

Well, my kart has a spherical bearing loaded that way with the steering column passing through, but thats not a heavy duty application... I guess just a good impact can take the bearing out of its seat, so its not the best thing to do.

Maybe you are looking for an axial bearing:

[Greg Locock]

First up I recommend careful selection from Aurora's ranges. Their top end ones are a bit pricey but can be twice as strong as some of the others.

Secondly, high load capacity and long life are the enemies of friction. If you need low friction (and for a suspension you do) then you need to do some research.

If we call the axis of the stud the x axis, and the axis of the hole through the ball the z axis, then the Z force rating is a compromise between high articulation about RY and RX, low friction and so on. Aurora say 15% of the radial force rating.

They also make a rod ends with different sized threads to cope with the real world issue of bending in the shank. As such Carroll Smith's 'no tie rods in bending' rule has been obviated.