My next project is an aluminum Softride Powercurve, and I've just noticed that the down tube took a hit right at the braze-on for the shift cable guide, and it has caused a creased dent in the down tube. Now I'm thinking maybe I should just bin it? It's cosmetic damage, no apparent cracks.

I'm not sure why you're posting if you aren't going to post a picture.

Damage is often cosmetic, until it isn't. IIRC Softrides have only a single frame member between the headtube and the seat tube/bb. Unlike a failure in a normal diamond frame where the break is supported by the "other ends" this down tube's complete failure will leave only a handful of cables holding the front and rear together. Andy

Assuming you are referring to the frame with two tubes between the head tube and the BB then a crease that is
transverse across the tube would be much more concerning than a longitudinal crease. Aluminum does take
well to bending and sudden failure is a higher risk than with a steel or Ti frame. A pix would help.

One other thing, a few friends have had softrides and there can be resonance at certain cadences with the
seat beam resulting in a lot of bouncing. Kind of weird when you are behind such and it occurs.

Kind of hard to photograph, but you can sort of make out the crease running parallel to the tube, right down the middle. There is also a crack in the paint.

By the looks of the frame, it looks like it has a conventional downtube, with the leaf spring mounted along the top tube, like this. Is that the style of your frame? If so, you have a little more margin for safety with regards to what Andy said above. With the paint still on the frame, it's hard to know exactly what the impact looks like underneath. I imagine the Softride bikes put unique stresses on the frame; I imagine something like that would be "fine" on a traditional frame with the rider's weight on the seat tube, but the Softride design may be more sensitive to something like this (I don't know for sure).

If anything I would think that the swinging seat, that Softride has, will lessen the force peaks in a traditional down tube and possibly increase the forces in the top tube. I have only worked on a few dozen over the years and saw issues with seat beam pivots and the frame right about the pivot "braze on".

The few tandems I've come across with beams have a curious reaction from the riders. Stokers really likes the suspension, captains liked that their stoker was happy but some disliked the added body movement. Andy

Thanks for the feedback. I feel that structurally the frame is OK, and it appears that the paint cracked when the tube flexed inwards.

That damage would be much less worrisome to me, mostly cosmetic, but a stressor that eventually,
probably years from now may crack.

As to the resonance bouncing of the beam with certain cadences I have seen this on both a singleton
and a tandem. As Andy noted, stokers kind of like it but the pilot can find it disconcerting.