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Heim versus ball joint

March 12, 2024 — BarryK

A few weeks ago, I admired Tomek's "Street Fox" DIY recumbent trike front suspension:

Those type of joints are known as "Heim" joints, as distinct from normal ball joints. These are also known as "Rose" joints in Britain.

There is at least one trike manufacturer using the same technique; Stein Trikes (based in Serbia). See video about the "Wild One" trike front suspension and a snapshot from the video:


I did some reading-up on Heim joints. Two major problems; they do not have high axial strength, and secondly they can wear out quickly.

That bottom joint is the main concern. You can imagine, if the wheel hits a bump, there will be a severe upward force, that the lower swing-arm will resist due to the shock absorber, hence strong axial force trying to rip the joint apart.

Then riding in inclement weather, rain and dirt will get into the joint. On dry dirt roads, dust will get in.

So, it seems to me, that bottom joint will have a limited lifetime. But does that matter if the joints are cheap?

I purchased three different types of joints, to compare. Firstly, Heim joint:


I bought the cheapest, m10 thread and hole diameter, they cost only about AU$3.50 each and AU$2.50-ish postage. Postage remainded about the same for bigger quantity. Ha ha, compare with RS Components here in Australia, they are asking AU$45 each (plus postage?). eBay AU vendor wants AU$25 each plus AU$10 postage.

Maybe these ones from Aussie vendors are higher quality. Perhaps they have higher axial strength. The couple that I purchased from Aliexpress look okay, just eyeballing them.

I also purchased this ball joint:


As far as I can make out, it looks like the ball has been inserted from the bottom, which means that it cannot be pulled out. That is an important point for the bottom joint in the swingarm that you can see in the Stein Trike photo.

I found, however, that the join is incredibly stiff, and when I did get it to move, it did so very jerkily. It would probably loosen up in time, I suppose. The Heim joint, in comparison, moved freely, without feeling loose.

The third one I purchased is this:


Also a bit stiff to move, but again I suppose it will loosen up with usage. I pulled that little spring clip out, thinking that would allow the ball to be pulled out; but no, it is locked in, as shown in this section view:


I don't think that this would last if used upside down. For that bottom joint in the swingarm, there would have to be a bracket so that the joint can be bolted on right-side-up.

Both of those last two have rubber boots, so very good protection from water, dirt and dust.

Having a respite from the DIY trike project while my thumb heals; it has been an opportunity to rethink the design. Lots of thoughts, will post when something definite is decided. Definitely don't want to start from scratch; will use parts already constructed, such as the steering knuckles.

One very interesting bit of information; Stein Trikes did design a full-suspension leaning trike about 9 years ago, named "Wild Wave". There were prototypes but it never went into production. From a couple of short videos, it looked like the leaning was purely by body lean, not via the steering mechanism.   

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