Andy Reichert Posted July 8, 2015 Share Posted July 8, 2015 I thought it would be helpful to mention and show the common wheels sizes in use for 16.5 mm under the NMRA (US) HO standards and which have some relevance to so called "modern" commercial 00/EM/P4 wheels in the UK. From the top downwards, here are examples of: Proto:87 36" dia. NMRA RP 25 code 72 36" dia. NMRA RP 25 code 88 33" dia. NMRA RP 25 code 110 33" dia. shown fairly close to together, in order to indicate the relative widths and flange sizes. Link to post Share on other sites More sharing options...
Arthur Posted July 8, 2015 Share Posted July 8, 2015 Aren't they upside down?? Link to post Share on other sites More sharing options...
Andy Reichert Posted July 8, 2015 Author Share Posted July 8, 2015 Aren't they upside down?? Apparently some browsers settings may show the image that way. They are the right way up on my screen. If it appears upside down on yours, then just read the text that way. Andy Link to post Share on other sites More sharing options...
Arthur Posted July 8, 2015 Share Posted July 8, 2015 Thanks Andy, I have noticed that a lot of the images you post appear, to me anyway, upside down, my browser I guess. Link to post Share on other sites More sharing options...
RMweb Premium melmerby Posted July 8, 2015 RMweb Premium Share Posted July 8, 2015 Thanks Andy, I have noticed that a lot of the images you post appear, to me anyway, upside down, my browser I guess. What browser are you using? (I'll avoid installing it!) Cheers Keith Link to post Share on other sites More sharing options...
Jeff Smith Posted July 8, 2015 Share Posted July 8, 2015 For those not wanting to do the sums an HO 36" wheel is 31.5" in 4mm, and 33" is 28,8". These are not useful sizes for 4mm however a Kadee On30 24" disc wheel (RP25-110) is 38". Current Hornby 4mm (spoked) wagon wheels are also 38" and approximate to RP25-110 but have a larger diameter flange. see http://www.rmweb.co.uk/community/index.php?/topic/93079-non-magnetic-wheelsets-for-uk-rolling-stock/Post #45 for more details. Link to post Share on other sites More sharing options...
Arthur Posted July 8, 2015 Share Posted July 8, 2015 What browser are you using? (I'll avoid installing it!) Cheers Keith Safari on iPad, never happened with any other images, weird. And only with very recent ones of Andys. Link to post Share on other sites More sharing options...
Andy Reichert Posted July 8, 2015 Author Share Posted July 8, 2015 My reason for posting the picture has more to do with compring the flange sizes/profiles of the different wheels. The RP 25 profile was developed for RTR (deep flange - no suspension) wheels and applies the same shape and relative size of flange, but in proportion to the tyre width. If you look closely, you should be able to see the wider flange on all but the Proto:87 wheel at the end. Note that RP 25 (Recommended Practice 25) is not a mandatory part of the NMRA standard, but a recommendation for "best practice" in terms of model running quality. In my own personal way of describing mutiple different wheel sizes and types, specifically avoiding the obvious ambiguity of using "fine scale", the RP 25 profile is always a RTR or coarse flange. Where as the P:87 wheel (and it's P4 Brethren) with almost scale flanges, are "near scale" and typically require suspension. When dealing with four types as shown (or 5 if you include 00-P), the concept of their being just a single choice of one "coarse" and one "fine", just doesn't apply. I know that what some posters here think as "modern RTR" here is considered "fine" by some in some other places, whereas what may be thought of as "fine" here has at least two different wheel sizes to choose from. So I generally use the wheel width (aka "code") to be clear. I'll be back later to list the (effective) flange widths for each types(and therefore their coresponding flangeway needs. Andy Link to post Share on other sites More sharing options...
Andy Reichert Posted July 15, 2015 Author Share Posted July 15, 2015 The effective flange widths of the wheels shown, and the related expected safe running model frog flange way width are as follows: Wheel Profile Width Flange max FW max Proto:87 (scale) code 63 0.014" 0.028" ( Note: 0.022" actually used for nearer scale flange way appearance) NMRA RP 25 code 72 0.020" 0.032" NMRA RP 25 code 88 0.025". 0.040" NMRA RP 25 code 110 0.030" 0.050" The RP 25 wheels are defined as 10% wider than their FW max figure, to make allowance for a blunted frog vee up to the 1/2" point, or build tolerances of the wing rails. Note that blunting a vee beyond the 1/2" point will exceed the extra wheel width allowance and re-introduce some degree of wheel drop. Andy Link to post Share on other sites More sharing options...
Ravenser Posted July 15, 2015 Share Posted July 15, 2015 For clarity's sake , for British readers: RP25/110 is what is nominally fitted to modern OO RTR stock from Bachmann, Hornby and Heljan (As far as I'm aware Dapol is much the same) . The Chinese factories interpretation of the nominal standard is subject to manufacturing tolerances (eg the back to back may not be exactly 14.40mm , and may not be exactly the same on all axles of the same model..) The use of this specification for British OO RTR is not surprising , since it is what is normally found on US outline HO, which the Chinese factories are accustomed to making. The DOGA OO Intermediate wheel standard mirrors RP25/110 http://www.doubleogauge.com/standards/commercialwheels.htm RP25/88 is approximately equivalent to the EM 1979 wheel profile , which is the nominal standard for Gibson and Ultrascale wheels supplied for EM and OO (ie the suppliers use the same wheels , set to different gauges/back to backs to supply the two markets). The DOGA OO Finescale wheel standard mirrors the EM1979 wheel profile, with suitable adjustment to gauge and back to back . Tenshodo motor bogies are normally to RP25/88 Markits (Romford wheels) claim to use a profile called RP25/100 - which is not shown on any current NMRA datasheet, but which Markits say they found in an issue of a US modelling magazine from the early 1960s Lima and pre 2000 Hornby wheels were significantly coarser than RP25/110 It is worth noting that Hollywood Foundry supply their Black Beetle motor bogies to both RP25/110 and RP25/88 profile. I suspect that the same applies to their Bull-Ant motor bogies as well. It's a good idea to check that you are buying the wheel profile appropriate for you when buying their products [i'm not sure why this has suddenly appeared in my New Content screen following deletion of cookies by something - I assumed this was a current topic but the wheel equivalents may be useful anyway]- Link to post Share on other sites More sharing options...
Jeff Smith Posted July 15, 2015 Share Posted July 15, 2015 As I recently had cause to measure current Hornby wagon wheels (R8094 spare wheels pack) I can confirm that they are, RP25-110, tyre dia 0.5", flange dia 0.575 (RP25-110 should be 0.55"). So in fact not quite RP25-110 but near enough. Dimensions in imperial as they are likely to be versions of HO wheels as suggested above. Also for clarification the figure after RP25/ 88 or 110, is the tyre width in thou". Peco points are designed for 110 or greater - thinner tyres tend to fall into the frog gap. Link to post Share on other sites More sharing options...
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