# Large Scale Wheel Standards



## Fuelrush (Dec 13, 2009)

Hello, I'm trying to figure out the wheel standards of Large Scale. I'm new to large scale and the various scales within. I plan to try to model a 2-8-2 narrow gauge loco at 1:20.3. 

I've been browsing and printing off all of the NMRA standards I can find regarding the scale and I'm a little confused. I'm not really sure what my modeling falls under.


Standards I've found: 


"Large Scales Standards DRAFT v1.6" - Has min, and max specs for wheel dimensions for "Large Scale/LS"

"S-4.1 Wheels, Proto & Fine Scales"- Has min, and max specs for wheel dimensions for "Proto: 20.3", "Proto: 20.3n3" and so on to smaller scales.


"S-4.2 Standards, Wheels, Standard Scale" - Has min, and max specs for wheel dimensions for "F," "Fn3," "LS,"LSn3"


"S-4.3 Wheels, Scales with deep flanges" - Says "G models typically have a minimum tire width of .271. Also G uses the same wheel geometry as #l gauge wheels.


Each section has some specs fairly close to each other and some quite a bit different. I don't know what my 1:20.3 narrow gauge is considered. G, Proto: 20.3n3, LS, or LSn3, Fn3 or something else all together.


If someone could point me into the most widely used NRMA spec for scratch builds like I'm doing it would be very appreciated. It would be great if several people would chime in. Maybe with some explanation to these standards. Thanks you!


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## Greg Elmassian (Jan 3, 2008)

Use S-4.3.... 4.1 is for prototype and fine scale. It's virtually impossible to have trackwork outside that will handle this. 


The difference between 4.2 and 4.3 is only the flange depth... stick with the deeper flanges until your trackwork is really good. 

Regards, Greg


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## altterrain (Jan 2, 2008)

Do ya want a shelf queen or a reliable runner? If the latter then forget about NiMRod-A's and see Bruce Chandler's thread below on how it's done - 
http://www.mylargescale.com/Communi...fault.aspx 

-Brian


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## East Broad Top (Dec 29, 2007)

Forgive me if I differ a bit from Brian's opinion of the NMRA's specs--since I was one of the principle architects of the standards.  (And no, I'm not even an NMRA member.) 

Anyway, Greg has it right. Go with the Hi-rail standards, with a tread width of .271". Flange width as wide as the specs allow, a .03" radius fillet between the wheel and flange, and a flange around .090" deep. That's on par with what Bachmann and Accucraft are using for their wheels in terms of flange depth. 1:20.3 running on 45mm track is by the NMRA's standards called Fn3 (F scale, narrow gauge, 3' gauge specifically) There's a separate set of standards particular for Fn3, but they're essentially identical to what's shown on that proposal. 

Later, 

K


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## Jack - Freshwater Models (Feb 17, 2008)

I think the longest lived and most reliable wheel standards is that of the G1MRA. This standard was in existance long before the NMRA and has been used around the world. In modeling narrow gauge to a larger scale just increase the tread width which doesn't matter but maintain the flange profile. Big flanges are ugly and don't necessarily perform better. 

Jack


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## xo18thfa (Jan 2, 2008)

There are actually 2 G1MRA standards, "standard Ga 1" and "fine Ga 1". I use the "standard Ga 1" and never have a problem. 

http://www.gaugeone.org/Misc/STANDA...%80%99.pdf


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## East Broad Top (Dec 29, 2007)

Big flanges are ugly and don't necessarily perform better 
Much depends on the track over which you're running. Small flanges don't like uneven track, so if you're going to use G1MRA's flange width and depth as a benchmark, just make sure your trackwork is up to the task. I agree, the G1MRA standards are time-tested, but I'm also positive G1MRA rolling stock would roll right off on the average US garden railroad. We're just not used to building track that well because we've always had uber-deep flanges as a crutch. The two very much go hand in hand. 

If I had to design an "ideal" wheel profile, it'd be .271" wide (scale 5.5") with a flange width of around .075" and a depth of around .090". I'd include a .030" fillet between the flange and the tread, and taper the tread to 3 degrees. This is a bit deeper/wider than G1MRA's flange maximums, but it is small enough to look scale under the 1:20 equipment, and deep enough to withstand a fair amount of unevenness. (Incidentally, Accucraft's wheel profile is very close to this.) 

Later, 

K


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## Greg Elmassian (Jan 3, 2008)

I used to believe that large flanges did not help much, especially when I remembered back to the RP25 days, where the flange looked tiny, and everyone said they would not work. 

But, Kevin made a comment about flange depth recently, and I went out and made up a 45 car freight and ran it around my layout and sat at various locations peering closely at the track and the wheels. 

I have a place where there is a 9.5' diameter 180 degree bend and then a steep downgrade. The track is on temporary supports here, so it's not perfect, but what surprised me was how often the wheels would lift just a little bit and how important the flanges were. 

Now you can say my track is crummy, and smaller flanges would work fine if I had better trackwork. I would respond: how many people can run a 45 car freight up a 3.4% grade, and down a 5.5% grade for hours on end, i.e. my trackwork is most likely better than most. 

So, there is something to be said for the depth of the flanges. How big should they be? I'm experimenting. But there's an important point in what Kevin said. 

Regards, Greg


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## Jerry Barnes (Jan 2, 2008)

I like my trains to stay on the track and my 10' rule pretty much reduces the flange size! So I'll take a larger flange, may not look good sitting still but will keep running and running. Spending my time outside with my trains re-railing them all the time is not my idea of fun.


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## Semper Vaporo (Jan 2, 2008)

Posted By Jerry Barnes on 14 Dec 2009 07:49 PM 
I like my trains to stay on the track and my 10' rule pretty much reduces the flange size! So I'll take a larger flange, may not look good sitting still but will keep running and running. Spending my time outside with my trains re-railing them all the time is not my idea of fun. 

Yeah, but just think how much more "Hands-On" that is!


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## FH&PB (Jan 2, 2008)

If you're modeling in 1:20.3 scale, then just use the G1MRA profile. It matches the AAR wheel profile so closely that you would swear that they just took the AAR drawing and reduced it by 20. 

If you're modeling in 1:30 (or 1:32) scale, which is what the G1MRA standard was developed for, of course the flanges are oversized, but as has been noted, it's worked for garden railroaders for many decades. 

When I was asked to give input on the NMRA wheel standards, the inclination of the person I corresponded with was to just adopt the G1MRA spec, since it was already a de facto standard. I can't remember now whether that happened (help, Kevin?) or if it was modified. The G1MRA standards are online, however, so you can do your own comparisons. 
http://gaugeone.org/Misc/STANDARD%2...%80%99.pdf


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## East Broad Top (Dec 29, 2007)

Here's a comparison of the NMRA proposed standards (target values) as compared to G1MRA: 

Gauge 
NMRA 1.772" 
G1MRA 1.772" 
(equal) 

Track Check Gauge 
NMRA 1.652 
G1MRA 1.654 
(difference of .002") 

Span 
NMRA 1.537 
G1MRA 1.555 (max) 
G1MRA states no minimum, only a maximum. The Maximum tolerance on the NMRA's standard is equal to G1MRA's stated maximum. The NMRA's minimum of 1.535" is wider than commercial switches from LGB, Aristo, et. al.. The specific target point was chosen so to allow legacy products with ultra-narrow (non-compliant) back-to-back spacing to still at least have a hope of operating through these switches without going bump. 

Flangeway 
NMRA 0.116 
G1MRA 0.120 
(difference of .004") 

Flangeway Depth 
NMRA 0.118 (min) 
G1MRA Unspecified 

Wheel Check Gauge 
NMRA 1.633 
G1MRA 1.634 
(difference of .001") 

Back to back 
NMRA 1.575 
G1MRA 1.574 
(difference of .001") 

Wheel Width 
NMRA 0.236" - 0.271" (wheel width is meant to be proportional to scale, so 1:32 wheels would be on the 0.236" end, while 1:20.3 would be on the 0.271" end. 
G1MRA 0.236" (max) 
(G1MRA standards do not allow for a scale wheel width in scales larger than 1:32) 

Flange Width ("standard," "Hi-Rail") 
NMRA 0.059, 0.074 
G1MRA 0.060 
(difference in the "standard" set, .001", .014" in the hi-rail set.) 

Flange Depth (maximums, no minimums specified, but good luck running without them.  ) 
NMRA 0.066, 0.118 
G1MRA 0.079 
(NMRA depth is smaller by .013" on the standard side, .037" larger on the hi-rail side. 

The differences in flange proportions stems from the simple fact that of all the departures from G1MRA standards noted in wheels produced by the major manufacturers, flange was by far the most common. Manufacturers repeatedly stated their customers wanted the deep flanges, and would not abandon them. The deep flange standards are a compromise aimed at hopefully gaining support from the manufacturers, while still reining in the mishmash of profiles on the market today. 

Later, 

K


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## Torby (Jan 2, 2008)

I thought standard were banned in Large Scale.


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## East Broad Top (Dec 29, 2007)

I thought standard were banned in Large Scale. 
Just adherence to them.  

Later, 

K


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## xo18thfa (Jan 2, 2008)

Posted By East Broad Top on 15 Dec 2009 12:20 PM 
Here's a comparison of the NMRA proposed standards (target values) as compared to G1MRA: 

Gauge 
NMRA 1.772" 
G1MRA 1.772" 
(equal) 
.
.
.
. (save space)

.
. 


shmash of profiles on the market today. 

Later, 

K 
Maybe we can just average all this and make MLS "guidance". Just kidding, but there is not that much difference really. I wonder if the discussion about flanges has more to do with back-to-back dimensions on the wheels being out too much and the fact that we are trying to pull very long trains with very long cars thru unrealistically tight turns.


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## samevans (Jan 3, 2008)

BTB is not the be all and end all. It should be larger than the track span dimension (width over guard rails ) for fairly obvious reasons. More importantly the wheel check gauge (BTB plus nominal flange width at root) should be equal to, or very much more preferabl, less than the track check gauge (span plus flangeway, the latter being thegap between running and guard rails). This is so that the guard rail does its job of keeping the flange/flange root from striking the apex of the crossing (sometimes rereferred tio as a 'frog') or worse still picking up the apex and passing down the wronmg side of the crossing. In the first case the faster the train the more significant the striking becomes with a greater tendency to flip the flange out of the rail and cause derailment. There are plenty of prototype pictures of what happens when a loco passes down the wrong side of a crossing... 

As to standards not being relevant to Large Scale, next time you have you automobile serviced hope that the mechanic does not try to get a UNC thread down a UNF hole. I suspect you would not be happy with the damage that an improper mechanical fit would wreak on your vehicle any more that you would be happy at the damage to a) an expensive model b) the model you spent many hours constructing because of an improper mechanical fit between track and wheelset causing a derailment at a switch. 

Sam E


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