Standard Gauge Track Spacing

The 87 came out to keep track centers at 7 1/4", 42,57,72 ,87. The 84 does not conform, no reason you can't use it with a straight section added in, if you want concentric then you need to use std 72 std 87.

About a year ago SGMA members collected extensive data on the underhang and overhang of Standard Gauge engines and cars on curved track.  At several shows menbers had noticed that some locomotives and cars with significant overhang and/or underhang made contact with each other on our corner modules when passing each other on our then standard 72 and 84 mainlines.

Obviously, a change was needed as contact is not something you want to happen between your expensive Standard Gauge trains.  However, we didn't know how much change was needed to correct the problem.  To determine this, SGMA members collected overhang and underhang data on our Standard Gauge trains going around our then standard 42, 72, and 84 mainlines and on a proposed replacement for the 84 mainline, i.e., an 87 diameter curved track mainline.  Fortunately, the data collected indicated that replacing the 84 mainline with an 87 mainlne would solve the contact problem at least for the trains on which the data was collected.  Based on this research, SGMA members voted to change our outside mainline standard from 84 to 87. 

However, I should note that there may still be a contact problems between trains passing each other on SGMA's current 72 and 87 mainlines for those trains on which overhang/underhang data wasn't collected.  For example, I don't belive data was collected on the Brute's new supersized passenger cars.

A table containing the overhang/undehang data for a lengthy list of Standard Gauge trains was developed but to date I don't believe it has been posted on the SGMA website.  I will try and make that happen.

Bob

The 87 curve on the SGMA layout is still a tradeoff. It is always better to go bigger but there are restraints. The two biggest factors for the 87 curve is equal spacing of all 4 track radius. 2nd the distance to the edge of the layout.

There will still be times when trains will be stopped on the 72 loop straights so that that the really big stuff can run on the 87 loop. The 30" Showroom cars can fit a State car inside of it. However, STG is almost 1:26 scale and a 80' Passenger car scales out to about 36". These 36" cars do exist and have run on SGMA layouts.

You can contact Kirk at USA Track. StandardGaugeTrack@Gmail 

Thanks for the replies. What I really need is more specific information on what kinds of combinations produce contact on 84/72 combinations, so that I can see what might actually happen on our layout. I'd love to see the SGMA table - if that is available, could you possibly e-mail it to me? My e-mail is in my profile.

Thanks.

Okay, for what it's worth:

On my layout I have all standard gauge tinplate sectional tubular track.  There is a 72" horseshoe curve, composed of (8) sequential 72" curve pieces. Outside of that there is an 84"curve.  This is composed of (4) 84" curve pieces, then a cut 3-1/2" straight piece at the curve apex, then another (4) 84" curve pieces.

At the apex of the curve (at the 3-1/2" straight piece) the center rails of the two tracks are 8" apart center to center.  The center rails are also 8" apart at the far ends of the curves.   Because as noted in posts above the 84" curves are not exactly concentric to the 72", on each side, equidistant from the 3-1/2" straight piece, halfway from the center to the far ends of the curves, the distance between the center rails bulges slightly to 8-1/2" center rail to center rail.

Given this setup, I put on the inside, 72" track, what I believe to be my locomotive with the biggest overhang, the new Super 381.  On the outside 84" track, I placed my longest-wheelbase car, a state car, which should have my biggest underhang.

At the point on the curve where they come closest, there is 2-1/8" space between their closest points - the leading corner of the 381's cab swinging wide of the 72, and the center of the side of the Maryland state car cutting the corner of the 84.

I have made a tactical decision not to try to run my Brute, and not to buy the showroom cars.  They are just too big for everything else on the layout.  Even though my layout is around 30 x 38, I would have to redesign and rebuild everything and not use most of the accessories. Big is cool, but there is such a thing as too big, IMHO.  So I have no data for you on the super big stuff.

Hope this is helpful.

Thanks hojack, that is an extremely useful piece of information. State cars and a Super 381 are about as big as it's likely to get on our layout. We run a Lionel Hiawatha and a Boucher Pacific fairly regularly, which are comparable in size and overhang. I note that your curves are slightly farther apart than a fully concentric circle due to the straight section, but thanks to your very complete information I can take that into account in calculating my track spacing. 

Nobody in our Standard Gauge group is contemplating buying a Brute, as far as I know. 

Remember, with Hojacks system the straight leading into the 84 curve will be 1 3/4" longer than the straight leading into the 72 corner. This is 1/2 the 3 1/2" straight track.

F&G, you're right, there is an adjustment at that location on the curve as well.  I used very few 14" straight pieces, cutting most of my straights out of 36" lengths, so I did not have short pieces at those locations.

Hiawatha, yes, the 3-1/2" is a cheater piece, but the way the 84's laid by themselves, I didn't feel comfortable with the clearance.  What I didn't mention is that inside the 72 curve is a third line. I made that out of 72-42-72, and then 72-42-72 again.  That inside line is definitely for smaller trains, shorter cars - although I did set my accessories and scenics back so the state cars do make it around.  Look kinda ridiculous doing it.

I didn't know about Kirk at USA track until after I had my track laid.  His curve sizes give more and better options, plus his track is so much better quality than the current 11-series MTH.  I got a load of extra ties from him and they are made of serious steel.

dave

I did my home layout like Hojack with a half straight to make things wider. I went wide enough to fit the 440 signal bridge at the apex of the curve. The next to final step will be to repaint and add scenery. At least painted sawdust.

Here is a shot of 87,72,57 and 42 together. I like the even spacing better. The module before the corner has a transition track to carry the 42 mainline out to the 57 mainline.