According to NMRA S-4.2: "Wheels, Standard Scale": 3: "HO fine wheels will work on HO standard track but HO standardwheels will not work on HO fine track."To my understanding this should mean that the H0 fine wheel is supported bywing rail at turnout crossing (at double flangeway).According to S 3.2 and S 4.1: This should be true: 2x Fmax(norm) Tmin(fine) + Bmin(fine) + Nmin(fine)Unfortunately there is no Tmin(fine) specified. From the above one couldhowever conclude that: Tmin(fine) = Gmax(norm) + Fmax(norm) - Bmin(fine) - Nmin(fine). Tmin(fine) = 0.661" + 0.050" - 0.581" - 0.086"This results to Tmin = 0.044"Now Tmin(fine) should be about twice the Tmax(fine) 0.025" -- i.e. no goagain!If it is permissible to use RP25/86 or H0 (fine) wheels, why the standardwheel is specified as PR25/110 and why the "Standards gage" recejts RP25/86wheels?I must really be missing something -- what? Please advice!Pekka Siiskonen

I think you've found the/a hole in the NMRA standard.

Here are the dates:S-3.2 has a date of January 2006 on the standard: has a date of January 2006 on the standard: has a date of July 2004 on the standard:

How come NMRA HO fine wheels work on NMRA HO standard track?

Sep 21, 2007 23 Replies

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Whodunnit 18 years ago

Amen! Some folks just like to bitch about the NMRA...

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Mark Mathu 18 years ago

Here are the dates:

S-3.2 has a date of January 2006 on the standard:

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S-4.1 has a date of January 2006 on the standard:

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S-4.2 has a date of July 2004 on the standard:

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Mark Mathu 18 years ago

Howard , where would the NMRA committee which is in charge of RP25 code 88 wheelsets fall on that list? Mid-Scale Standards? Special Standards? Mechanical Standards?

RP-25 (wheel contour) seems to be pretty independent of scale.

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Howard R Garner 18 years ago

Good question. I do not have the answer. But drop a message to the mid scale person and see what he has to say.

Howard

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