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[quote user="beaulieu"][quote user="smattei"] [quote user="marcimmeker"]I've admired those huge threads about British railroading or the coffeeshop. So I am going to start one here about European railroading in general. Marc Immeker[/quote] A question I had im my head from long time: why did european RRs choose to use 4 wheels (2 axes) freight and passenger cars (even after having tried the 8 wheels cars in 1860-80s, e.g Wuertenger and some ante SBB swiss rrs), and only after WW1 started using again 4 axes passenger cars (after going with the 3 axes ones)? They are still building 2 axes freight cars today (but the percentage of 4 axes increased a lot in the last 20-30 years). US RR started almost from the beginning with the 4 axes, and never changed. What are the advantages (and the down side?) of this choice. Sebastiano [/quote] There are many reasons to use 2 2-axle bogies (trucks), the reason that US railroads went to them early is due to the poorer quality of our track. Rolling stock with bogies handles bad track better. As to why the Europeans stayed with two axle stock longer, I can think of three contributing factors. One, speeds were low for freight and distances were short. Two on the Continent frequent wars probably  meant there was greater demand for the money to rebuild the railways, certainly there was an incentive to make freight cars last as long as possible. Three in many cases lack of competition, so little or no innovation. I think now that open access is taking hold you will see most freight cars built with capacity, up to the maximum weight allowed. Many of the current 2 axle freight cars have no more weight carrying capacity than a highway truck. [/quote] There isn't necessarily a correlation between maximizing load factor and using 2 axle bogies.  Indeed, the opposite is true - load factor actually improves with single axle bogies vs two axle bogies because a lot of extra parts are disposed with, e.g. no need for a center plate et al.  It is the rigid wheelbase of railcars with single axle bogies that limits their use for cars that require a solid platform at maximum length.  Single axle bogies work well for cars that come in multiple platforms wherein the commodity is aggregatable such as coal (the Southern 100 4 unit coal car comes to mind), or with lighter weight items where the space between platforms can straddled such as the Iron Highway ro-ro car.  If you follow the discussion on the Iron Highway thread.... <A HREF="/TRC/CS/forums/878549/ShowPost.aspx">http://www.trains.com/TRC/CS/forums/878549/ShowPost.aspx</A> ...you will see that single axle bogies were paramount in many of the innovations that were meant to increase load factor.  The TTOX/Four Runner TOFC cars, the Southern 100, the Iron Highway, the Trough Train, all used single axle bogies in whole or in part (althought the original Iron Highway actually used axleless independent wheels, which was a primary problem with the concept).  The consensus seems to be that single axle bogies work fine for cars with a wheelbase of 25' or less, or if implemented with some form of articulation to offset the drawbacks of a rigid wheelbase.  It should be noted that these innovations were eventually scrapped not because of the single axle bogies, but because of other quirks related to non standardization of parts. Standardization is the primary reason US railroads have stuck with the two axle bogie over single axle or three axle bogies.  In a somewhat ironic twist of historical fate, back a few years ago before they went bankrupt, the US bogie manufacturer ABC-Naco had developed an axle set with independent suspension that could be offered in single axle, two axle, and three axle configurations.  All the parts were interchangable with each other, and the independent suspension gave a superior ride quality over the US standard three piece bogie.  This innovation would have allowed complete standardization of any axle configuration for bogies, which may have finally paved the way for wider acceptance of cars which use single axle bogies.
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