Frequently Asked Questions

Is Proto:87 compatible with standard HO?
No. Standard HO flanges will not fit through Proto:87 flangeways. Proto:87 wheels are too narrow and spaced too far apart to pass through standard HO frogs without derailing
Why not make a standard that is close to prototype, but compatible with standard HO?
We didn't take this approach because it would have implied another compromise standard. Sooner or later someone would have been asking for a standard that is as close as practical to the prototype. If you want to model to some HO-like standard, go ahead, but please don't confuse the world by calling it "Proto:87."
Is Proto:87 simply a matter of shrinking the prototype dimensions to 1:87.1 scale?
Not quite. Proto:87 allows for reasonable manufacturing tolerances that would disappear if the prototype were merely factored down.
I'm using the code 88 wheels, they look pretty good, why would I bother with Proto:87?
First of all, wheels are only the start of the equation. Once you've seen it, Proto:87 track is far more noticeable than finescale wheels. Secondly, you should note that code 88 wheels are outside the HO standard, which allows for wheels no narrower than code 108. Code 88 wheels will not operate smoothly on all standard HO track. Many people do have success with them on a subset of HO track (I'm told Shinohara and Micro-Engineering work), but they have implicitly chosen a tighter standard than HO.
What's the minimum radius?
Because the flanges are closer to the rail heads, the minimum radius is definitely broader than standard HO. A general rule of thumb is that you're going to be looking at something approaching prototype minimum radii. The NMRA published an excellent technical note on Proto:87, which includes several tables for minimum radius. You should look at them before starting your planning! The Fremo:87 group probably have more experience than anyone, and they set their minimum mainline radius to 2m.
What's the difference between HOpur and Proto:87
HOpur is a German standard created by shrinking the prototype by 1:87. A surprising discovery as we built out the Proto:87 specification is that HO scale is different in North America. In Europe, it is defined as 1:87, whereas the NMRA defines HO as 3.5 mm to the foot. This makes for a couple hundredths of a millimetre difference in the bigger dimensions, such as wheel back-to-back. In practice, we've found that it's hard to detect such a small difference with real models, and HOpur equipment seems to run fine on Proto:87 track and vice-versa.