Originally Posted by sixtiescycles

Hi, Wayne,

Saw your note about wishing for a response. What can I say besides the fact that we're a small business with just a few people doing everything, and one can easily spend their entire waking hours attending to forums and blogs? I wish I had more time for this stuff, as it's rare I don't have a response in mind. Your questions are also somewhat off-topic, since the thread is (supposedly) about frame stiffness--and I have plenty to say on that topic, too!--so I'll try to keep things succinct. Thanks for your patience.

We really don't have a problem with chipping from gravel and the like, whether during riding or on a roof rack or such. Powder coat does a very good job of protecting the frame in that regard. It's more like a plastic film than paint, in the sense that it's somewhat flexible and absorbent of small hits. In the rare case where a nick or ding is deep enough that it's down to the base metal, our recommendation is to clean the area well and use touch-up paint to match.

In answer to the "hammer to the top tube" question, I've pretty much answered this before, but to reiterate, magnesium has several mechanical properties that help:

--The low density allows use of unusually thick tube walls that tend to be more dent-resistant than, say, a 0.4 mm wall thickness steel such as used on lightweight frames. The problem is the so-called "beer can syndrome," where a thin-walled tube either dents easily or, worst case, buckles under load. The rule of thumb with steel, for example, is a maximum 50:1 ratio for average-strength alloys and as high as about 75:1 for high-strength alloys. The ratio for a 28.6 mm diameter tube with 0.4 mm wall thickness is 72:1. The top tube on our frame is 48 mm in diameter and 2.0 mm thick, for a ratio of 24:1. There's more to it than that, but it should be apparent that this contributes to dent resistance.
--The powder coat is flexible enough that the dent your grandson made has to be pretty serious indeed before the powder coat delaminates from the frame. I recently saw a Paketa single bike frame that was run into a parking garage while on the owner's roof rack, and even though the dents in the down tube were so bad that the frame was destroyed, the powder coat was still intact! Practically speaking, the tube will likely be ruined before the finish is compromised (mechanically, at least).
--In most cases, small dents won't compromise the mechanical integrity of a magnesium frame at all. Magnesium is quite tolerant of normal abuse (running into a parking garage falls out of the category of "normal") and makes an excellent choice for a travel bike, for example. My own new Paketa tandem is being built with S&S couplings for these reasons.
--As for warranty following a crash or other serious incident, that has to be on a case-by-case basis, and I don't think any manufacturer would argue otherwise. In the immediate instance, the crashed single bike was well out of warranty and we negotiated a reduced-price replacement frame as a good will gesture. Again, my guess is most manufacturers would do the same.

Just to get back to the thread topic, I have done quite a bit of frame stiffness testing our our bikes along with others I had available. Ask me a few questions about that next time ;-)