Hi there,

I'd like to know what is the min and max distance between axles to be capable of moving on all type of tracks (straight, curved, flexible). I would like to build as long as possible a single axle wagon and a double axle wagon.

Edited October 15, 20177 yr by RTL7

Well, that depends. For a start, for the double-axle wagons you mention, the pairs of wheels at each end can typically swivel on bogies to allow them to take corners. This makes it possible to have any practically length you want. Look at some of LEGO'S sets to see what I mean. 

For single axle, or 'fixed' wagons, the distance is around 8-10 studs between the wheelsets, so 12-14 axle-to-axle. You won't find fixed wagons with longer wheelbases than that in official sets, and by that point you're starting to push the wheels further than they would like anyway. You can increase that distance by allowing the axles to swivel a little, with an elastic band or spring to return them in-line with the wagon when it leaves the curve. There are plenty of examples on the Internet. 

In both cases there isn't really a minimum distance, but less than 4 studs doesn't really make much sense. I think the best thing is to try them out using some wheelsets, plates of various lengths and some track, to see what is acceptable for you. 

@ColletArrow said it all - maybe one more thing to consider: With 2-axle bogie design (your 2nd picture) you can have indeed almost any length. When going through tight curves, even more so through S-type curve segments there is a lot of "overhang" to consider (depending where the bogies are located on the frame also the couplers may swing out considerably). This is particularly true for switch points. Depending on the design of your switch point throwing mechanism (replacement of the original yellow lever of the switch stand and addition of extended pull rods) this limitation can be overcome of course. It just depends on the lateral distance to the next track.

Best
Thorsten