By "X-frame" I mean a frame which have a tube (call it tube 1) connecting the seat tube to the (roughly middle of the) down tube, and another tube (call it tube 2) which connects the head tube to the (roughly middle of) tube 1. Tubes 1 and 2 take the place of a conventional straight top tube. These frames are more commonly seen on full suspension bikes.
These frames are touted as affording larger standover clearances for given effective TT lengths compared to conventional top tubes. There are other claimed fit advantages but this is the main one.
Obviously if the tubes used are large and/or thick enough, there shouldn't be any issues on adequacy of strength of the frame. However, it seems to me that the welds connecting tube 1 to the down tube, and connecting tube 2 to tube 1, carry shear loads; and that tube 1 and the down tube will have bending loads imposed on their midsections (when translating compressive load on conventional top tubes to these crossed tubes). Can anyone see any issues or inherent flaws for such a design? Those who have knowledge of frame component load magnitudes might be able to illuminate.
Can anyone see any issues or inherent flaws for such a design?
while you can compensate for the stress patterns you identified by "over-engineering" at the relevant locations, the fact still remains that the traditional "diamond" frame principles give the best strength/weight ratio. the shortest distance between two points /is/ a straight line.
talk of needing increased "standover height" baffles me. if my feet are on the pedals, i don't understand its relevance. if my feet are on the ground, i'm not moving, so i still don't get it. if someone can explain, that would be great!
imo, the only real reason manufacturers go for these whacky designs is to create something instantly identifiable, even when the logos are all spattered with mud. curvey-tubed hetchins are another much older example of this strategy.
talk of needing increased "standover height" baffles me. if my feet are on the pedals, i don't understand its relevance. if my feet are on the ground, i'm not moving, so i still don't get it. if someone can explain, that would be great!
In offroad conditions, standover clearance is important on occassions when one needs or has to stop; halfway up a hill or small steep incline, or upon encountering a large obstacle. Getting off the saddle and putting both feet on the ground which may be uneven can cause clearance issues between the top tube and a sensitive part of people's bodies, if the standover height of the frame is close to the rider's inseam length.
talk of needing increased "standover height" baffles me. if my feet are on the pedals, i don't understand its relevance. if my feet are on the ground, i'm not moving, so i still don't get it. if someone can explain, that would be great!
In offroad conditions, standover clearance is important on occassions when one needs or has to stop; halfway up a hill or small steep incline, or upon encountering a large obstacle.
Or, more importantly, picking your way down some awful gully and coming to a point where you say 'no, *I'm* not going down _that_'. Braking hard in those conditions is a sure way to go down it head first so it's clip out and feet down...
Quoted message said:
Getting off the saddle and putting both feet on the ground which may be uneven can cause clearance issues between the top tube and a sensitive part of people's bodies, if the standover height of the frame is close to the rider's inseam length.
