I have seen many posts from various members about this subject. It is difficult to trouble shoot via the inter net, because trains are dynamic models, and it is sometimes necessary to actually see what is happening to caus the derailing. This will be a long post, but I hope that I can put in a comprehensive tutorial that anyone can use to trouble shoot derailing problems on the railroad. First off, I'm going to suggest that there are three areas where we can find the cause of the derailing of our cars and locomotives. #1 tracks. #2 incompatibility between rollling stock and radius. #3 rolling stock problems. I've found the problems will generally fall into one of those areas, and the plan is to put up a comprehensive post to cover all contingencies if possible. On second thought, I think I'll do a general over view in this post and then do the detailed analysis in each area in subsequent replys. How to figure out if a problem is track related, rolling stock related, or incompatibility between rolling stock and track radius. First, does all rollling stock derail regularly at the same place on the layout? If the answer is yes, you probably have a track problem. Is the problem section curved or straight track or is it a switch? Does only some of the equipment derail at the same place, but other equipment works fine there? If the answer is yes, does the rolling stock that has problems have something in common? For instance, do 40 foot and 50 foot cars work fine, but 60 foot-85 foot cars have problems? Yes? Probably a radius problem. Do you have one or more cars that derail in a particuar spot if they are coupled directly behind a specific type or size engine, but seem to work fine when hooked to other engines or with other cars between them and the engine? Yes? Probably a compatibility problem between radius and equipment. Do your 4 axle Gp & f type type locomotives and 4 axle freight cars work fine through a section of track(maybe even a straight section), but 6 axle diesels, steam engines, and 6 axle passenger car trucks derail? Yes? It could be tight radius problem or a bump or dip in trackwork that knocks the long trucks off the rails. These are all of the questions I can think of to ask to help narrow down the source of problems. If anybody thinks of other questions that should be asked, post them and I will edit this post. I am now going to do 3 replys to this post discussing track problems, radius incompatability problems, and rolling stock problems respectively. If I overlook anything that should be included, just post it and I will add it to the appropriate post. My goal is to have a thread in the tips section with 4 posts that will be comprehensive instruction on how to trouble shoot, find, and repair any problem anyone might encounter in keeping their trains on the tracks.