Aftermarket A-arm failure, also tie rod failure

[FrenchToast]

Recently saw one fail in two places. Don't remember the company. It is welded tubular chromoly and no longer made. The flaws, if present, are not apparent in visual inspection. If you have such an arm I would recommend sourcing replacements from another supplier.

A-arms, as well as all suspension and steering components, should be chosen carefully (I've seen OE tie rods fail as well). Stock A-arms often fail on cars that have been lowered. If you choose aftermarket ones research them to make sure they are satisfactory for your application and meet adequate strength and construction criteria.

All this is to say that important components such as suspension and steering pieces should be carefully chosen (by a qualified technician) and regularly inspected.

[RedBaron]

Thanks for the heads up!

[DannoXYZ]

Can you post some picture of failure areas?

Chromoly tubing is amazing stuff (look at millions of BMX bikes, thousands of Tour de France bikes and countless Ducatis). But it has to be well designed into 3D shape and welded properly (back-flushed, along with post-weld annealing). Doesn't take well to too much heat, thus brazing is used to preserve as much strength as possible in thinner gauges.

[FrenchToast]

Originally Posted by DannoXYZ

Can you post some picture of failure areas?

Chromoly tubing is amazing stuff (look at millions of BMX bikes, thousands of Tour de France bikes and countless Ducatis). But it has to be well designed into 3D shape and welded properly (back-flushed, along with post-weld annealing). Doesn't take well to too much heat, thus brazing is used to preserve as much strength as possible in thinner gauges.

The tubing turned out to be fairly thin and the welding was not adequate. No idea if it was annealed.

After looking at it, it was concluded that the failure point originated from a poor weld and poor material dimensions. Overall geometry of the design was likely not ideal either.

There are pictures of a similar occurrence on RL. Seem to be about a half dozen failures that have occurred.

[DannoXYZ]

Yeah, saw on RL link, thanks!

Weld looked OK as it didn't crack or fail parallel to weld. But design not adequate for load. Too small diameter tubing along with too thin wall-thickness. For something like this, you'd want butted/conical tubing that got larger in diameter with more wall-thickness as it approached ends. Increasing diameter by +10-15mm overall would help quite a bit. There's also tubing with extra wall-thickness at ends along with helical reinforcement ribs.



Then there's ovalized tubing with extra wall-thickness along major axis for more load-handling in that direction. Would place this tubing with major-axis horizontal in this design. Or aero-elliptical such as used on open-wheel cars. The 2-3" major axis section will definitely handle those braking loads much much better.