Without running a full stress strain analysis on a set of tubular a-arms I'm going to have a hard time backing this up, but my degree is in aerospace engineering and I have successfully designed, constructed, and raced using tubular a-arms. Provided someone looked at some equations when they picked the tube wall thickness, they're substantially stronger than stock. Even if they didn't, as long as they didn't use paper thin tubing, they're stronger. In fact, if they just picked a standard tubing diameter, its likely they're several times stronger than they have to be. When the design team I was on ran the equations for the tubular arms we built I found that to meet the strength requirements we needed we could use tubing that was literally too thin to weld to the threaded ends we were using. Granted, it was for a much lighter vehicle, but I actually had to tell them that I wouldn't be able to TIG weld the design spec thickness to the solid rod ends, the tubing we ended up using was twice as strong as it needed to be.
The stock a-arms are prone to flexing and cracking, and I have seen it. Typically welds do not break before the tubing they join bends, but this depends on a lot of things. For one, if the tubing used was thicker than it needed to be (someone overbuilt, actually pretty likely), then the bending load for the tubing might be higher than it is for the butt weld that joins the tube to the ball joint retainer, especially since the length of the tubular arm is quite short from an engineering standpoint. Weld strength is also based on the size of the weld, both thickness and length, and the welds on the a-arms are relatively small, CAP's particular design using a butt weld is not the strongest. And of course a cold weld would also cause major problems. Loading conditions and the accident involving the RR are obviously a unique situation. Also note, despite the tubing being relatively small in diameter, the tubing itself does not appear to be deformed at all in that particular instance.
The factory did the cheapest thing they could to meet the minimum standards they came up with, and that was 40 years ago. The factory was looking at bottom dollar, period, and on top of that they really do have an equation balancing lawsuits to production costs. I wouldn't bet on them. You need to look no further than any type of autoracing to see which design is stronger and lighter. It would be exceedingly simple, for example, for F1 cars to use a single form carbon fiber arm that looked like one of our stockers. It would require a single mold, could be produced without any seams, and would be really simple to make and produce. But they use a tubular design. Why? Stronger, lighter, and for the instance of F1, more aerodynamic. I'm not aware of any aftermarket stamped steel a-arms, all are the tubular design. This definitely isn't for ease of construction, a stamped arm requires a machine to be set up a single time, after which you could run hundreds of items. Tubular arms require someone to set up a jig and weld every single time.
Take a look at the construction of your tubular a-arms before you buy them. I was lulled a little bit by the fact that the CAP arms look pretty much like all the other ones out there, but having them in hand now there are a few simple things they could have done to make them stronger, I notice now that a lot of the other arms have some type of gusset joining the tubular arms to each other and the ball joint retainer. If you have CAP arms, take a look at the welds. If they look good, you shouldn't have any issues. If you don't like the way the welds look, start saving up for a new set of arms, or take action to improve on the weld. If you want to run your stock a-arms feel free, but don't think for a second that your stock arms can't/won't fail just because they're "stock".
Topic: Tubular upper control arms, are they as safe as stock? (Read 1881 times)
