Just been offered a replacement bike after suffering this failure for the second time on my Strida 5.0. (Tube replaced under warranty the first time) I’ve had the bike for 2 & 1/2 years.
Interestingly, the second failure was preceded by a persistent creaking from the bottom bracket area. I couldn’t see a crack though until the tube failed catestrophically (for the bike not me). Inspection or the failed tube shows dirt on some areas of the broken surface so I must conclude the were fine cracks present for some time. If your Strida appears to be creaking from the bottom bracket, inspect these weld joints very carefully.
In my opinion the walls of the bottom are to thin and the welding process has created a weak point.
While waiting for a decision I’ve been thinking about reinforcing the bottom tube by filling it with Epoxy Resin filled with glass bubbles to form a syntactic foam. Clearly this would invalidate the frame warranty but should prevent this failure at least. I can’t think of another way to reinforce this tube without introducing stress points elsewhere.
I’ve been told that the replacement bike, Strida SX, is “an improved version with an EN Standards frame.” I can’t find any mention of EN standards in the 5.0 manual or at Strida.COM. If the bottom tube on the new frame has been redesigned and is genuinely stronger I won’t need to worry about modifying it…