2 rail vs 3 rail: Why the flange difference?

"What about 3 rail demands those huge wheel flanges?"

    Just the very tight turns that 3 rail is designed for. When the curves get that sharp it's too easy to pull a scale flange off the rail. Three rail equipment can run fine with scale flanges as long as the curves are broad enough..DaveB

Those deep flanges are what keep your trains on the hi-rail track through those tight curves, and especially through turnouts. Put 'em on the track and run 'em.

If you switch to scale wheels, you WILL be doing some tinkering with your track and especially the turnout. The scale wheels will find every bad spot in your track.

I don't think a lot of people realize that standard 3 rail .100" flanges actually ride on the bottoms of 3 rail turnout frogs. If your flanges are more than +/-.005" from that depth, you'll see it.

I run some scale flange stuff but tend to avert my gaze when they traverse my switches.

Hirail/3RS is just poaching the O gauge tinplate standards of yore for basic infrastructure. All else is refinement.

Norm your right. This is why I've modified the frogs on my scaletrax turnouts and am slowly converting to 2 rail atlas 1/48 with N scale 3rd rails that are Almost unnoticeable.

I think the biggest reason is the round top rail. It has been around for over 100 years, so it's pretty firmly entrenched. I believe Gargraves was the first to offer track with a more realistic profile. Scale trax and Atlas came along much more recently. Even Fastrack has that rounded top.

They really are toy trains in spite of all the new scale equipment. The leopard can't change its spots.

As for the 2 rail wheel sets, they better be insulated, or you'll have a direct short.

Actually, 2-rail wheelsets only need to be insulated if you are going to use only two rails. Once you arrive at at point, you have left 3-rail scale completely.

I think I understand the need for insulated wheelsets on 2 rail.

The instant dead shorts and breaker trips without insulated wheelsets are a real buzz kill on a 2 rail layout.

A third rail enables uninsulated wheel sets to provide detection for signal and crossing control and even CTC in the same fashion as prototype railways.  That is a nice advantage of our old school power method. 

But why are "scale" wheels not used on 3 rail? What about 3 rail demands those huge wheel flanges?

Deep flanges were common in HO and 2 rail O scale until the 1980s.  As others have noted, flanges and switch frogs have to be dimensioned to work together.  Backwards compatibility was a bigger deal in 3 rail O scale in the 1980s since there were so few truly new products. 

One can make a good argument that the modern era in 3 rail O scale began in 1994 with the introduction of the MTH scale Challenger.  Since then we have seen many new locomotives, cars and layouts all built around minimum O-72 curves.  The track on most of those layouts have T rail profiles and Magnatraction is not the selling feature it once was.  While we have moved forward in many ways the tinplate flange and frog dimensions have stayed with is and have considerable market inertia.  RP-25 flange dimensions on 3 rail T headed track are possible, especially on O-72+ layouts, but the backwards compatibility issues have kept 3R RP-25 in the realm of the do it your selfers.

You should try a MTH 2-3 convertible engine with scale wheels sometime. The difference will be in pulling power and the actual width of the wheel. 3-rail wheels are a little wider and have traction tires instead of magne traction now. 2-rail wheel sets will work but will also spin if the train load is too heavy. 2 rail engines rely on weight to keep the wheels from spinning.

Just to be clear, 2 rail must be insulted on the wheels, Each wheel contacts one leg of power if they touch each other directly, its effectively laying a screwdriver across your power terminals.  

(unless you run catenary, or batteries) 

3 rail was a method to transfer electricity easily, with no special wiring on reverse loops and you can use un-insulated wheels/axles. A serious toy, but with toys, ease and reliability are great assets.

 All toys had a natural state of overkill built in back then. Production abilities, costs, & materials played a design roll too. It worked well enough for a long time.

 As production developed, the wheels became solid, but didn't change shape much. Super O would have likely led to more scale 3 rail flanges had it caught on enough.  

 There have been lots of closer to scale flanges over the years. But it is of more interest to a scale minded person. Lots of people just don't look at them that deep unless asked too, and some prefer the reliability of pizza cutters.

 Yea, despite the flange size, that flange angle just might be helping the tiniest bit in ride up prevention in those tight 0-27 turns that can allow a train to go places it "cant" in scale.