Athearn HO wheels - changed to RP-25 standard in 1963

I never really paid much attention to Athearn wheel sets, but I know they had at least two sizes for rolling stock, 33" for freight and 36" for passenger cars. They may have also had a special size for intermodal (28"?). These would have been plastic wheels, with passenger car wheels having one metal wheel per axle for lighting elelectrical pickup. The diesel wheels were usually metal 42" diameter wheels mounted on stub axles. I believe the RDC may have used smaller wheels (36" ?), but these were for the rubber-band drive, so they would have been mounted on a drum, slightly smaller than the wheel diameter. The dummy locos had plastic wheels, probably 42" diameter, so the coupler height would match powered locos, but since I never had many dummy's myself, I'm not real certain. There may have been some anomalies that I'm not aware of, since Athearn products were in productions for such a long time, and the engines especially, went through some design changes.

Athearn probably had some of the best designed drives, considering running quality and ease of assembly for production purposes. Far and above, a superior product of American engineering.

Bill in FtL

Here are my actual measurements on common Athearn-style HO wheels. I have bunches of each kind, just the wheels on axles without the truck assembly. These are spares acquired secondhand and I don't know what cars they were on originally. I've used some of these wheels to upgrade misc older HO cars.

smaller freight wheel tread dia 23/64" = 0.359" scales out to 31.3"
flange dia 55/128"= 0.430" scales out to 3.06" flange depth

larger freight wheel tread dia 3/8" = 0.375" scales out to 32.7"
flange dia 7/16" = 0.438" scales out to 2.72" flange depth

passenger wheel tread dia  51/128" = 0.398" scales out to 34.7"

I'm measuring with vernier calipers which are accurate to 1/128". The question is: why the slightly different sizes of freight wheels? On closer examination I discovered the flange depths and profiles are slightly different. I reckon Athearn modified the wheels to better conform to NMRA recommended standards at some point, maybe around 1970??

The difference in size between the smaller and larger freight wheels is so slight, you wouldn't notice it without measuring. The passenger wheels are noticeably larger, and also obviously different because they have one metal wheel and one plastic wheel on each axle.

I also have some of the larger freight wheels on brass axles, otherwise identical - who made them? Some folks wanted non-magnetic axles for easier operation with magnetic uncouplers.

MDC freight wheels appear identical to Athearn. My MDC cars from 1970's - 1980's have the slightly larger 0.375" wheels. I understand Cox was a rebranded Athearn product, maybe they had some variations on standard Athearn?

In the real world 33" wheel diameter is standard for most freight cars up to 70-ton capacity, 36" for 100-ton, 38" for 125-ton, 28" on some piggyback cars to lower the deck.

I've always liked the Athearn wheelsets because they have the reliable NMRA RP-25 wheel profile, they are uniformly round with smooth finish, the steel needlepoint axles run true and roll freely. Sometimes the wheel gauge needs slight adjustment to conform exactly to an NMRA wheel gauge.

I've encountered some of the supposedly better metal replacement wheels that had rough treads and flanges that were prone to derailment. And some metal wheels on plastic axles that weren't always true. I had bad results with Central Valley trucks [1970's] because the wheel treads had visible machining grooves which were derailment prone, even though the trucks were sprung and equalized. Athearn wheelsets were good performers and good value.

I run moderately long HO trains on a mountain layout with sharp curves and steep grades. Performance is reliable with good smooth wheels properly gauged. Vintage three-rail O-gauge is sometimes a challenge in this regard because of sloppy standards.

Anyone else out there who is interested in these details and has information to add?

I believe the slight change I noticed in the Athearn freight wheel sizes (as explained previously)  was to reduce the width of the flange base, so the wheels were more compatible with tighter standards for switch guardrails, and to reduce the flange height to be closer to scale. At the same time the wheel tread diameter was increased slightly to be closer to exact scale for typical 33" wheels. I suspect the change was made back around 1970 but that's a rough guess. Another guess is that it may have been in response to updated NMRA "Recommended Practices" standards at that time.

If anyone has more info on this I would be interested to hear it.

From the Athearn website, this notes a change in Athearn wheels years ago:

http://www.athearn.com/About/

1963:  Athearn introduces freight cars with RP-25 wheels.

But I don't know to what extent the NMRA may have revised the RP25 specs through the years because their website shows only the latest revision. We can thank the RP25 specs for the tracking reliability of American-designed HO equipment. Unfortunately 3-rail O-gauge trains have not had any comparable standardization of wheel and rail specs.

Today I bought a secondhand copy of Greenberg's Guide to Athearn Trains  (1987 first edition). I picked up a bit more information about Athearn product development through the years:

... in 1963 ... there was the adoption of the NMRA RP-25 wheel design, which ... provided a more realistic wheel appearance without sacrificing good operating characteristics ... Athearn introduced the RP-25 wheel sets on a series of freight cars with new road names ... Athearn also in 1963 began a transition from the traditional sprung trucks, which by then featured the new RP-25 wheel contour, to the present-day solid-frame trucks.

[For a time Athearn had used a rubber insert instead of individual tiny springs in the sprung trucks, before changing to a simpler rigid-framed truck moulded as a single casting].

As far as I can tell, Lindberg was an early leader in adapting the RP25 wheel contour standard. Their cast-delrin, sprung trucks, with needle point axles and RP25 wheels, are STILL top of the line in looks and performance.

Lindberg is a hobby name I'm not at all familiar with. I'm interested in how some of the brands merged through the years. Thanks for the lead ...

http://ho-scaletrains.net/id34.html

"Certainly one of Lindberg's most popular items, above is a 1964 ad for the RP-25 Wheelsets."

Could be that 1964 was the year for Lindberg, however, I've noticed that all of my Lindberg literature that I've collected is essentially the same literature printed/distributed year after year. Some items advertised in their catalog was never (apparently) released. (Such as the hopper car and tank car.) Thus, dating exactly when they adapted RP25 will be difficult. I still have three of the cars from my original set I received Christmas 1962, and they have RP25 contours. However, that doesn't mean that I didn't change them out over the decades, and simply do not remember it.

So, until I can find something more conclusive other than a comment by a fellow enthusiast (such as the above caption), I'm still inclined to think they adapted very early on and the others had to get on the bandwagon, OR, some of the mfg'ers adapted at nearly the same time. For now, though, I will accept the 1964 date until I can comfortably prove to myself otherwise.

For sure, they were first with other innovations, of which I've listed before, but haven't time to list right now.

I'm off to work! See 'ya!