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Track Radius Question

Allan has an HO scale question for readers:

“I am finally going to make a start on layout, but my question is how much base board is required for a 22 inch radius track? I have to hang the base on a garage wall with a hinge system. My new home is limited in space so height of layout is limited to 160mm or 6 inch for rises and tunnels. I hope it works.”

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21 Responses to Track Radius Question

  • Joesays:

    I always lay things out on roll paper available at art supply stores.

  • Michael Gilmorsays:

    With a 22″ radius, diameter of the circle is 44″, allowing some edge distance, minimum board is 48″ or 1220 mm.

  • Joe Tillmansays:


    The required space depends on the track plan. A simple oval or close approximation will need a width of 46 in. to 48 in width for 22 in radii curves by the time you get roadbed under the track and maybe some ballast. I had a couple of 4′ x 8′ layout using 22″ radii curves and they worked well.

    If you are looking at a looped-8 configuration, then you will likely need something like a 58- 60 in (236 mm) width to make the layout work and look well for 22 in radii curves. Depending upon construction, a looped-8 would be fine with 6″ rises and it would give you a long run.

    • Sheldon Clarksays:

      236 cm or 2360 mm?

  • Don Jenningssays:

    Well, – 22 inch radii is just under 48 inch diameter which is a full 4 foot. So to answer you question ,
    I would use a 4 foot piece of board (that is square) and cut the inner space not wanted or used for the railroad.
    I hope that help you. Ask someone else to help -assist- you in cutting the board.

  • Sheldon Clarksays:

    The stated radius of curved track is measured in the middle of the sleepers (ties), so the space taken up by a circle of 22″ radius track will be about 45″ or 46″. Unless you are going to lay track at a very acute angle over the join between the pivoting board and the fixed element, you need to add on the width of the fixed part, say, 6″. For aesthetic reasons, and for the sake of realism, you don’t want the rails to come within about 6″ from the free edges of the board. This gives a total width of 58″, of which 52″ would be pivoted. Obviously, the width of the fixed part will govern the maximum height of any features on the pivoting board (including trees, telegraph poles, wind pumps, etc.). The hinges will need to be placed above rail level and the level of any scenery along the join; this can be done by fixing a pair of timber blocks at each end of the join, one on either side of the join and at appropriate intervals between the ends. These blocks can be disguised as piers for (removable) bridges or by covering them with removable buildings.

  • Billsays:

    22″ radius is usually measured to the center of the track. So you are close to 23″ on the outside. Add a bit for the base and a 4 foot wide board is the absolute minimum.
    6 inches is lots of clearance for HO. My concern would be if you are planning to use a 4×8 foot panel supported along one edge (hinge) and a couple of legs at the outside corners. You will probably have excessive deflection (sag) towards the outside middle. You have a couple of options, add enough legs to eliminate the deflection or add 1×4 on edge (and maybe a few across) to stiffen the panel. The second option is probably the better solution but may eat in to your 6″

  • Peter Whitlocksays:

    You have a bigger problem by ‘hinging’ your layout. As noted by others, to accommodate 22″ radius your layout will be 48″ + 6″ for tunnels & buildings + 2″ clearance to keep your layout from smashing against the wall. So that is a 56″ wide layout. There is no way that you will be able to comfortably reach the hinged side in the event of derailments. Secondly, features that reside nicely on the horizontal (when the layout is in the down position) are not guaranteed to stay in place when the layout is raised. Tried hinges & quickly scrapped it.
    2 suggestions: 1) do you have the headroom? Rig a pulley system to raise & lower your layout. You can leave your rolling stock on the layout – saving time. 2) shelf layout with 2 fold up loops at the ends. Or can make a point-point switching layout.

  • Rudysays:

    If you go from a straight stretch of track immediately into the 22 inch curve, the train will look like a toy train going around the corner. If you plan to slowly easy into the 22 inch curve, by gradually decreasing the radius until it hits the 22 inch mark, it will look more realistic. However, it will require more space. In that case, I would suggest to add a foot (about 30 cm) to the dimensions suggested.

  • Hank Tellersays:

    One of the most important questions to start is do you have a plan. It appears you should start with a 4×8 layout. Larger requires creating a bigger board which requires stiffening/support and makes any buildings, telephone poles, etc fragile. HO modelers tell me that using Kato HO Unitrack allows them to setup the set very quickly and, if necessary, take it down at the end of a day. In that case, until your layout is sceniced and made permanent you can keep the track in a box. With all turnout motors embedded in the roadbed and the electrical connections provider with Unitrack’s patented Unijoiners you will have no issues with electrical conductivity so you can easily set it up and run trains.This really allows the engineer to check out the layout for running trains without making soldered connections and other permanent feeders. Once you have a size check Kato’s site for layout suggestions. They have many under their drop-down menu for HO Unitrack.

  • Brad Beaupainsays:

    If your using newer/longer rolling stock you may need to consider using the 22 inch radius curves for more realism in how your consist negotiates the curves. The shorter 18 inch radius curves cause the longer rolling stock to “swing” out over the edge of the curve which is not visually appealing and not realistic as the cars should follow the shape of the track as it rolls over the curves. It may even cause derailments in newer cars not designed to navigate the shorter/sharper turns of the 18 inch radius. If you are using a standard 4 x 8 size layout you may only need to make slight adjustments to your layout buildings to accomdate the track. I know this doesn’t directly answer your question but if your layout to be able to accomodate all the various dimensions of the rolling stock, you will want the track to be able to accompdate the cars with wheel trucks that are set more apart. The older Tyco cars were set closer to eachother as they were based on 50 ft.scale cars but were fine (not perfect)for the 18 inch curves. The newer, longer cars wheelsets are farther apart (based on 60 ft scale) require the minimum of 22 inch to negotiate more naturally.

  • Randall Styxsays:

    As others have said, 46 inches is going to be your minimum width, and if you’re using 4’x8′ sheet stock, there will be no room for transition curves (not necessary, but nice). To provide stability and to create a fence to keep things from falling off onto the garage floor, you could put 1×6 boards on edge all around the perimeter. If you hinge the layout up against the wall, this frame would close off the layout and keep dust out in the stored position. If those 1×6 boards are attached to a 1/2 plywood, that would give you your 6 inches; but that frame would then be about 1/4 from the edge of your ballast (or cork roadbed), putting your trains very close to a “wall”. Long loco’s and cars might even touch the wall as they reach out over the ballast on a curve. You could dado the boards and fit the plywood into the dado to gain a little bit of space.

    You could also find sheet stock measuring 5 foot by 9 foot. Some retailers carry this because it is the standard size for ping pong tables. This would give you plenty of space for your 22 inch radius curves plus transitions, if you want them.

    If you have the headroom, I agree with Peter.

    • Randall Styxsays:

      With either a 4×8 or a 5×9 layout, it’s going to be difficult to reach the back half of the layout that is against the wall. One option is to have the layout come down onto a wheeled support and have easily removable hinge pins. That way you could roll the layout away from the wall during use and have full access to all sides.

  • Jeffsays:

    I’m going to second Hank Teller’s remarks about going with Kato’s HO Unitrack. Because the rail, ties and ballast are all one piece, it’s exceptionally easy to put together and take apart, as Hank indicated. Additionally, it lets you play around with your layout until you’re satisfied. Their 21 5/8″ radius is close enough to 22″, and if you get the urge to run a two track mainline, the next tighter radius is 19 1/4″ and the next wider radius is 24″. They’re using a standard 60 mm gap from centerline to centerline for their curved track. If you develop a yard, their radii gets as tight as 14 9/16″ if you need it. Depending on what you already have, Kato offers boxed starter sets with engine, cars, transformer and an oval of track including 21 5/8″ radius curves that will all fit on a 4’x8′ board (http://www.katousa.com/HO/Unitrack/starter.html). if you have room for a larger board, I also think Randall Styx has a good idea with a 5’x9′ board. Track always looks better when it’s well indented from the edge of the board, plus in the case of a derailment and rollover, your engine will have a better chance of not diving off the board. One last note, if you’re considering going DCC, you can get the oval track set by itself and Kato sells decoder and sound equipped engines. Just add the DCC power supply and throttle system of your choice.

  • David Stokessays:

    OK, I’m coming in late mate, but for 22″ radius 48″ is the norm – just so happens most MDF and ply wood sheets come in at 48″. Lucky you. If you are using one of the more esoteric type roadbeds, like the spline system the size of the board is not so important, but 1 board of 8 x 4 gives two 4 x 4 suitable for turnback areas on your layout. My own new layout will have 6 turnbacks, so 3 sheets of 15mm MDF. In between will be made up of whatever I have on hand.

  • Tim van Buurensays:

    Have you thought about a narrow shelf layout running around the wall of your garage?

  • allansays:

    hi all thanks for comments my plan had been to make a 10 x 5 layout and I am using atlas track code 100 biggest radius 22inch smallest 15 in for yards etc and mainline constructed from flex track I have small carriages I guess 50 foot scale and only my old intercity passenger train to use outside track only as this is a first layout for my boys 9 and 10 the goal is to get trains moving and not concentrate on typical type layouts the only request from them being tunnels and hills and a double track so more than one train can run my layout goal is forestry and freezing works
    I planned on a 140x 45 mm edge to help protect layout when raised and give enough height for a 2 level layout so thanks for all the comments they have been helpful and I hope I have clarified a little on my plans my main concern being the maximum radius needed for 22in track as I would like to rise the 22 inch track to the second level with an outer run around for the passenger train thanks again for all the comments I now know I will need 50 of the 60 inch layout for the 22 in track and this still gives me 5 inches each side for the run around track

  • Bob Schwormsays:

    Yes indeed. The 22 inch spec is the center line of the track. Consider the distance between rails, a bit more for the roadbed, and the ballast, this could cause the track to occupy at least 3.5 inches in ho scale. This means 1.75 inches added to the center line equals 22×2 = 44 plus another 3.5 inches and about 2 inches of margin on the benchwork. This comes to 49.5 inches. A curve radius should be at least 3 times the distance between truck axles on your rolling stock – worst case.

    You are specing your car’s trucks to be about 7 inches apart for a 22 track center radius??

    PS – Buy AnyRail software for an easy time of laying it all out.


  • John Byerssays:

    Do you have room to maybe make it 6 or 7 or more by 10 with a hole in the middle for the people? That way you could reach everything more easily and have quite wide curves, which look better and operate more smoothly. The 15″ in the yard is awfully tight for 50′ cars. do you have room to make the part that doesn’t hinge more than 6″? That really isn’t very much, but if it’s all you have, it’s all you have. Then, maybe Peter’s suggestion of running it to the ceiling and back down would be better unless you would need to raise it up to within 6″ of the rafters for clearance, although maybe you could plan it so taller structures went between the rafters.

  • David Broadsays:

    A said above the 22″ is the radius centreline, you need to allow another inch at least to the baseboard edge and double the result to get the diameter so 46″ , Now a lot of peoples bench work is not that accurate, and you want something between your prized loco and a 3ft drop to the floor like a piece of 1/8th ” ply or similar so go for 4ft when drawing your plans and 47 1/2″ when building your board .

    15″ Radius is tight in H0, Too tight in 00 where the stock is 1/7th larger and long wheelbases common, Bachmann UK GWR 0-6-0 chasssis wont get round 15″ and struggle with 2nd radius 18″ unless laid perfectly. Switches/ Points inder 2ft radius just about guarantee derailment when shunting.

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