My space for my HO layout is limited to a 4x8 sheet of plywood and I'd like to begin to run Amtrak Superliner cars and six axle locomotives on my layout. I know that a 22" curve will come close to the edge, but how close?
Are you
sure that:
1) H0 is the best modeling scale for you ?
2) That a continuous run loop is a necessity for you ?
3) a 4x8 foot rectangular table is the optimal use of your available space ?
The reason I ask is that a H0 scale loop of track on a rectangular table is a configuration that, while being common for beginners layouts, is a fairly inefficient use of space, especially in
small rooms.
A continuous run loop on a 4x8 foot table pretty much limits you to sharpish curves - that's a given that most people understand right away.
But it also imposes some other limitations on you that you may not have considered:
a) Reach vs footprint. 4 feet is too deep to reach across comfortably. So you either have to keep the layout out from the wall and a have an access aisle behind it, or at least have enough free floor space in front of the layout to be able to pull it out from the wall to gain access to the rear.
This means that a 32 square feet 4x8 feet rectangular table layout will fill up a floor space of about 8 x 10 feet (to allow 2 foot access aisles on three sides of the layout).
Basically - if you put a 4x8 feet layout into an 8 x 10 room, that entire room is spoken for - you don't really have room to do anything else in that room - an illustration of a 4x6 in an 8x8 foot room - same difference with a 4x8 in an 8x10 foot room:
b) More than 50% of the mainline length is taken up by the two turn back curves at the end of the layout, and possibilities for spurs and industries etc is pretty much limited to running a few tracks into the center of the layout - not much room for buildings etc between the aisle and the track on a 4x8 H0 scale layout.
c) Visually, if you don't put a view block of some kind (a ridge, buildings, trees, a back board with a painted sky or something) down the spine of the layout, you only have room for one scene for your trains - and in a few seconds you will see the train that just passed you going east heading west in the back of the scene.
If you put in a view block to create two visually distinct scenes, you will need to walk around the layout to see the other scene.
So, if you really want to do a continuous loop on a rectangular table, I would recommend seriously considering N scale.
You can do a continuous run loop with fairly gentle curves for longer rolling on a hollow core door - 32" deep and 80" (6 2/3 feet) long. In terms of what you can fit onto the layout, that is roughly the equivalent of a H0 scale 5 x 12 foot layout. Curve radius wise, a 15" radius curve in N scale is about the equivalent of 27" radius in H0 scale.
And you can put that layout into a corner - since you can reach 30" or so into the scene (at least with the aid of a chair to stand on). Making the layout a better room mate.
You still would have the challenge of oval loops on rectangular tables, though.
Unless you put in a view block of some kind (a ridge, buildings etc) down along the spine of the table, you only will have one scene visually - with the train first passing through the scene once in the foreground, and then a second time in the background.
And if you put in a view block, to actually
use that second scene, you need an access aisle to the rear of the layout, negating most of the advantage you won by having a shorter reach across the layout.
You would still have the advantage of gentler curves (about the equivalent of 26-27" radius curves for H0 scale) for longer engines and cars, though.
And you will be able to run longer trains - a medium sized engine is about 10" long in H0 scale, while an 85 foot passenger car is just under a foot long. A train consist of an engine and seven passenger cars takes almost 8 feet of length - ie the whole length of your 4x8 foot layout.
In N scale, those 85 foot passenger cars are about 6.3" long - and in 80" of track length you have room for a train consist of 10-11 passenger cars and an engine.
If your main goal is running longer trains and trains with long cars, going down in scale may be a very good idea.
And there is nothing that says that you have to do a continuous run N scale layout as a rectangle - one can e.g. do a folded dogbone put into a corner, and still not have too crappy reach and scenic separation:
Continuing on - if you want to do H0 scale, another option possibly worth exploring is to
not create a loop on rectangular table.
You can e.g build a quite nice urban passenger railroad station on a 2 foot deep and 18-20 feet long shelf along just one or two walls in a room, and focus your modeling on modeling trains arriving and departing (or trains "just having arrived" or being "just about to depart").
Depending on desired modeling era, you can have engines being cut off and serviced, mail cars being taken to the post office, express freight being taken to the railroad express agency, restaurant cars or sleepers or observation cars being switched out of the train (to go onto other trains) and so on and so forth.
Or you can build a small town with a depot and en elevator on e.g. an 8 foot long and 18" deep scene, and off to either side of this area you can one "drawer" with five tracks holding e.g. 5 eastbound trains on the left side of the modeled scene and and another drawer holding five tracks on the right side of the modeled scene.
You can now have a variety of trains passing through your small town. Dropping off cars that later will be picked up by another train, or spotting cars at e.g. a warehouse or a team track or an elevator in your little town.
In general, running a layout as a set of not so deep shelves (or on a set of not so deep tables) along the walls allow you to use far bigger curve radius even in H0 scale, since the center of the curve does not have to be on the layout - you are doing quarter circles instead of half circles.
Running along the walls, where you cannot see the whole layout at the same time also allows you to have visually distinct scenes along the various walls and a far longer run, and allows industries and buildings both behind the trains and between the trains and the aisle/pit.
Having a wall behind the buildings beyond the tracks also makes it possibly to model just one side of a bigger building or a bigger scenery feature (like a mountain) - since you don't need to find room for the rest of the building or scenery feature.
You can also run continuous run in H0 scale with fairly gentle radius by considering doing a do-nut shaped layout instead with the operator (and any spectators) located in a pit in the center of the layout, rather than walking around a rectangular table.
You get into the central pit either by ducking under a narrow section of layout in front of the door, or having a swing gate or lift up or lift out piece of track. An illustration, using the same room as in the 4x6 example further up in this post:
Anyways, there are lots of options for building a layout in a smallish room.
It is not necessarily a given that "all I can fit is a 4x8 foot H0 scale layout".
I would suggest exploring some other options as well - and see if you perhaps have other options than trying to run 85 foot H0 scale passenger cars on a loop of track on a 4x8 foot table
Smile,
Stein