We`ve had excellent luck with them over the years and we`ve sold more of them than anyone (except SPC). There are almost no bending forces on them,the loads are inboard/outboard and tension/compression. Upper arms are not weight bearing. The arms BTW have also passed extensive structural and FEA analysis. We run them on our own cars and have more than 50,000 hard street miles on some sets. One of our cars was in a fairly hard front end collision to the right front with no damage to the arms at all. In fact it didn`t even change the alignment!
One customer totaled his car going off an embankment into a stand of large trees at highway speed. The front end was toast and the frame was racked hard but the only damage to the SPC arms was one slightly bent ball joint plate (which we sent him a replacement for). The stock lower arm on the same side was bent beyond use. He ended up buying the car back and used the same SC&C parts on the new frame. Look at any AGT or GT1 road race car which are capable of far greater braking and cornering loads than our street cars and you`ll find SPC arms or ones very similar to them from HRP etc. This years American Iron Extreme champion Ernesto Rocco is running SPC adj. upper arms on his Mustang with Griggs non strut suspension. They`re also used on Factory 5 Cobras. Strength and durability are simply not an issue.
The adjustability and modularity are awesome because they let us tailor them perfectly to each application and align the cars with no compromises. Something not always possible with shims. That`s why most modern cars haven`t used shims for years.
Oh BTW David a few words of advice. SPC arms should not be used with stock spindles unless you use our tall ball joints and or the car is lowered quite a bit with springs. Their flat profile will restrict droop travel. The version sold by Summit and Jegs is supposed to be "direct fit" but I tested those arms for SPC several years ago and didn`t find them to work out very well. Because of that SPC assembles many application specific arms that we tested and speced out. These are available exclussively from us, SC&C. Used as part of our Street Comp suspension packages they`re darn hard to beat! Mark SC&C