The Great LEGO® Train Width Debate
If were to ask a group of LEGO Train fans what the "correct" width of a LEGO train should be, you'd probably get as many answers as there were pollers. LEGO has traditionally built their models 6 studs wide (there are a few exceptions to this however).
There have been some excellent discussions on LUGNET about what the "correct" scale should be.
John Neal wote in this LUGNET post:
You have 2 choices upon which to gauge your
scale-- the height of the minifig or the track gauge (the distance between the
rails). As John (Gerlach) mentioned, a typical US train is about 10 feet wide, and
standard track gauge is 4’ 8.5”, or about 5 feet (half of train width). Since
the distance between the LEGO rails is 5 studs, that would put you, as again
John (Gerlach) noted, 1 stud = 1 foot, or 10 wide. This is the true scale using LEGO
track gauge. That makes a minifig about 5 feet tall, and this would be perfect,
except for the unfortunate reality that the LEGO wheels are terribly small
at that scale, making 10 wide trains look rather funny.
So the question becomes how far do you want to deviate from the ideal
proportions (not considering the wheel size issue). 8 wide scale says that a
minifig is about 6 feet tall and the track gauge is a bit wider than standard,
but the wheels are about spot on in terms of size, and again as John (Gerlach) said, it is
the best compromise if you are trying to build as “realistically” as you can.
For some reason, I've always built my trains 8-wide. I never took
thought about what the correct scale should be, I've just always
thought they looked "right". I recently was lucky to have the opportunity to help develop a train set for the LEGO Company with 9 other LEGO fans. While I can't say much about the set until it is launched, I will comment on the difficulties for me to reduce my train building to 6 wide. We (the train builders group) decided from the beginning to keep the trains we built in scale with what LEGO had already produced in the past, which was, for the most part, 6 wide trains. At first I had trouble overcoming the initial compression that 6 wides required over 8 wides. After a few builds though, I quickly began rolling out more models, each one a little faster than the previous. For a moment, I entertained the idea of converting all of my trains down to 6 wide. It was done beautifully by Steve Ringe of the MichLTC and former "8-wider". These are some of the best looking 6 wide trains, in my opinion. Some advantages to converting everything to 6 wide are the amount of pieces and functionality. When you build 8 wide, you increase the amount of brick used exponentially, because you aren't just building wider, but longer and taller as well, which also increases the weight of the train. LEGO motors weren't designed to pull heavy loads because they are a "toy". I was really impressed with Benn Coifman's [Central Ohio LEGO Train Club's (COLTC)] feat of pulling 28+ train cars. This is something that I can only dream of with 8 wide trains. The other problem with big heavy trains is that the standard LEGO train controller can only output so much power. Once you put three or more motors on the same track, the controller begins to overheat quickly. Fortunately, we have overcome this by sprucing up the electronics in some of our train controlers which now output more current.
Another option would be to compromise between these two and build 7-wide. German LEGO Fan, Ben Beneke, has been promoting 7-wide train building for a few years. He has an excellent presentaion that he gave available here. This was it, I thought! This is how I'll start building my trains. I tinkered around in MLCAD with some designs and sketched roughs out on paper. The major problem with building 7-wide is trying to make everything work in an odd-numbered scale. LEGO train windows and parts are usually in an even number sized, so working them into an odd size model is difficult. Ben does build some beautiful trains, but most of his work is devoted to the steam era, and those models can get away with odd sizes. Spencer Rezkalla was able to pull off some nice looking 7 wide models, but they didn't end up being that much smaller than 8-wides, so besides the challenge factor, what was the point?
When I began toying with the idea to start making custom train kits, I wanted to make 7-wides so that I could reach a broader market. People with 6-wide or 8 wide layouts could easily integrate these models without much hassle. I've now changed my mind again, by not changing my mind. I'm going to stick with 8 wide because that's what I enjoy building, and what I think looks best. My future train kits will be 8 wide models, a niche in custom kits that hasn't been filled.
In the end, build what you like. The debate will go on forever, so have fun with it!