The essential difference – the wheels

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Wheels look better with Proto standards because to all intents and purposes they are identical to the "real thing". The photo on the left shows the "real thing" on a full-size grain hopper car in a siding. The right-hand photo, after a bit of Photoshop wizardry, shows what the full-size wheels would look like if they were made to a US National Model Railroad Association (NMRA) code 110 profile. If a UK commercial-standard wheel were substituted here, it would look coarser still. [Thanks to our Canadian friends at for permission to use these images. Their caption is: "See the difference between the two photos above? If not, then Proto 87 is not for you."]

Compare the wheels on this SAR broad-gauge 'OW' gondola car by member Nigel Gardner with the left one above and you'll see how faithful Proto wheel standards are to full-size practice.
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Here is a comparison of three wheel profiles: on the left, Proto 87, very close to the prototype profile; centre, Code 88, the fine version of the NMRA Standard S-4.2; and on the right Code 110, the NMRA wheel profile most commonly produced for the US, Canadian and Australian markets.
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Different though these profiles are, they do have a supremely important factor in common: a very specific transition, or fillet, between the tread of the wheel and the flange, which is matched by the profile of the rail-head. Early railway engineers recognised that wheels are stopped from derailing not by the depth of the flange but by the radius of this fillet. (Later, as speeds increased, they also "coned" the tread.) The Proto movement began when British modellers decided to replicate the shape of the fillet, getting away from the model wheel standards of the day that were essentially set by mass-market manufacturers: the transition between tread and flange on their wheels was abrupt, with no provision for a fillet. Even today, commercial British wheel profiles vary greatly and some brands continue this practice.

At the time when it was realised that the radius of the fillet needed to as big as possible, the NMRA standards governing wheels in the US did not provide for a fillet either. However, it was not long before the NMRA came to the same conclusion and amended their standards by specifying a value for the radius of a fillet, saying also that "radii at the edge of the flange should be as large as possible within prescribed limits".
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Not convinced about this wheel profile stuff?
Click on this image to see a video clip of it working at 500 km/h on a French TGV
After the Protofour standards were introduced in the UK, other Proto standards were introduced, one of which was Proto 87 for 3.5 mm to the foot scale. These fine scale standards embodied the same principles as Protofour, but with Proto 87 being seven-eighths of Protofour (i.e., in the ratio of 3.5 to 4). Later, the NMRA issued their own Proto standards after some US O scale modellers used true-to-scale wheel and track standards. The dimensions for the NMRA's Proto 87 were within a thousandth of an inch of the British dimensions for Proto 87, so they are interchangeable.

The NMRA later named their existing wheel standard "Code 110" (so called for the 0.110 inch distance between the front face of the wheel and the back of the flange). They also introduced other, scaled-down versions of (of which Code 88 has some following in HO) to partially address concerns about coarseness of wheels. They warned, however, that although "HO standard wheels [i.e., Code 110] will work on HO fine track (with adjusted [check gauge]), HO fine wheels (Code 88) are not standards on HO standard track". This means, in effect, that Code 88 wheels require their own track standards.

In 3.5 mm scale, P87 (broad gauge -- left) and NMRA Code 110 (standard gauge) wheelsets in the same archbar bogies.

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... and the track

Fine-scale standards are even more noticeable in track.

You can greatly increase the realism of track regardless of the standards you follow by using accurately sized rail and sleepers that reflect your particular prototype. However, it's when flangeways are seen -- in points and crossings which populate station yards -- that the realism of Proto standards is striking. The dimension for flangeways for standard HO scale is 1.22mm; the P87 dimension for flangeways is 0.58mm. The difference in actual measurements is quite small but the proportional difference in the two flangeway standards is large: the gap in P87 is only 52% of the gap in HO.
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A full-size turnout (South Australian broad gauge).

SAR broad gauge turnout made to Proto 87 standards.

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The most commonly purchased turnout in Australia and UK: Peco.

A turnout made to US NMRA S-4 standards.

Pros and cons of Proto scale

There is wisdom in the Canadian quote above, "See the difference between the two photos above? If not, then Proto 87 is not for you".

If a person doesn't often see full-size track and wheels, the perceived difference between the "real thing" and the coarser model standards may never become "front of brain". That's not surprising: we all suspend belief when we see a model railway, and for decades otherwise discerning modellers suspended belief for the truly atrocious appearance of track and wheels.

We know that railway modelling is a richly rewarding hobby that many people enjoy for the major part of their lifetime. True to human nature, modellers tend to challenge themselves to build and finish better-quality models as they progress. The immense improvement in quality of reproduction in commercial models has also driven a quest to make better models. The most common characteristic of people who become interested in Proto standards is therefore one of evolution in model-making goals: "I have always tried to achieve better detail in my models, and Proto 87 allows me to continue this level of detail in track and wheels".

Some modellers have come to the same conclusion but do not want to make a wholesale replacement of their existing pointwork. Our club has a number of members in this category, who like working as a group on the more demanding Proto modelling while being in the mainstream for personal hobby activities.

Did we say "more demanding"? Yes; Proto standards do make for more demanding modelling. That's the enjoyment for us but it can be a negative for some people.

So speaking of negatives, here are what many people think of as the "cons" -- which we agree they would be if we didn't enjoy Proto modelling as an end in itself.

  • Working on, or assembling, Proto wheels and track takes longer than in mainstream modelling, especially if you are used to buying as much as possible ready-made.
  • Under-the-track benchwork should be well constructed, especially to avoid distortion under extremes of temperature.
  • Components are more expensive than in the mass market.
  • You need to be more careful in construction, even though jigs take care of most aspects of achieving accuracy.
  • If you model the steam era and have large (8-coupled) locomotives, the truer-to-scale factor will require wider curves (1050 mm or more, compared with say 800 mm with NMRA standards). This doesn't apply if you only have diesel locos.
A commonly quoted "con" factor is: "Vehicle underframes and bogies have to be sprung or compensated". That isn't so. If track is competently laid, freedom from derailments is about the same as with standard NMRA track.

Here are the "pros":

  • As mentioned, for people who prefer the appearance of full-scale track and wheels, and enjoy the little challenges of fine scale modelling, Proto standards are another means of making our hobby deeply rewarding.
  • Following Proto standards results in a better-looking railway with no detriment to running qualities of vehicles.
  • For standard-gauge track (i.e., not turnouts), ready-made flexi-track (preferably a brand with finer rails) can still be used.
  • With many bogies, standard-gauge HO wheelsets manufactured to NMRA mainstream standards can be dropped out and replaced with broad-gauge P87 wheelsets, as in the photo above.
  • In the SA Protofour Group, some of our members regard Proto modelling as a sideline to their other hobby activities. For example, they may also be in a club (or have a layout) that uses mainstream track and wheel standards. We're not religious extremists, so we don't kidnap anybody's kids for departing from "the one true way"...
  • Being part of a group that has lots of camaraderie while enjoying the creation of railway models is something that's extremely valuable in this hurried world. Railway modellers invented "men's sheds" years ago!

FAQs about Proto scales and our club.

More on the background to P4 and P87.

Links and ideas.
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