David_H

Thanks Mike

Could you please post the data that you found? The image no longer displays so it is all lost. Thank you

I think that you may have perhaps misunderstood - from what I read in many postings "RTR" will run on OO-SF without modification. So if that does work for a modeller, and they have an existing OO layout, then they may decide that is easier than going to EM or P4. You'll have to ask them, of course, but I think I am pretty safe in saying that. It's just that perhaps "RTR" means different things to different people, based upon their purchasing history. I think maybe the distinction may need to be drawn between a US-based wheel, and others. I'm not familiar with the UK market, and I can only report my own experience with US-based products. But I do not claim that this also applies elsewhere. OO-SF modellers appear to be very happy with their choice. That would not be the case if they had trouble with RTR wheels, I think.

Hi Andrew - link is here. In brief, using published wheel standards, it appears that the US NMRA HO standard wheels only have a small overlap (0.06 mm) that allows operation through the narrower OO-SF frog. Furthermore, the NMRA has a "target" dimension to encourage manufacturers and modellers to aim for, and this dimension is at the top end of their back-to-effective-flange (BEF) range and outside the (greater than) maximum BEF allowed for OO-SF operation. Wheels that are wider than the allowed BEF will pick the point of the frog and try to go the wrong way through. Anecdotally, i.e., from the actual experience of actual modellers who were kind enough to reply to my posting, many US style wheels did work for people's OO-SF turnouts. If I may summarise for others (and please forgive me if I get it wrong), the consensus appeared to be that older US wheels were made to an older NMRA standard, now defunct, that does happen to allow for running through OO-SF. I went back and measured some of my locomotives (mostly recently bought) and found that five wheelsets out of the 22 measured would make the grade to run through OO-SF, the others were too wide. I had already measured (and reported on in an earlier post) a set of semi-fine code 88 wheels that I had bought from Reboxx. They are great looking wheels that come in a large number of axle widths so you can pick what works best, and meet the relevant NMRA wheel standard, but were all at the top end of the NMRA range and therefore kept picking the point of the frog when I test ran them through (this started my quest for more information). Having wheels too wide (or too narrow) is not necessarily a problem. It's an embuggerance, sure, to have to measure up and reset any errant wheels, and difficult to do for older steam locomotives. So I can see how, if a (UK) modeller's personal collection of rolling stock is already the right size, and if they know that they can purchase more of the same, that OO-SF holds appeal because no modification (apart from swapping out older wider wheels for slimmer looking ones) needs to be done. The problem arose for me because that important caveat - it works for UK wheels - was not made obvious. In my defence, I could find no actual data on what the requirements are for wheels to successfully run through an OO-SF turnout. In response to my plea for more information there is now written down data for the required maximum BEF. It becomes a simple case of working out what wheels work and what don't.

Hi Andrew - you make some good points. I have also been looking at OO-SF for nearly a year now. I have a slightly different set of dot points to you. In the spirit of avoiding the usual taking points, I'm happy to accept that different people can get different things out of a particular subject. So while some of my talking point might mirror your own, others might not - but that doesn't make me right and you wrong, it's just a different look at the same subject. And I hate this dancing around, so I'll just deal with the facts - at least as I see it. OO-SF is a track standard, not a wheel standard. It can be for anyone to use for any scale or wheels they can make it work, if they desire. Some, perhaps many, wheelsets can operate without modification. Anecdotally, many people have found that their wheelsets work fine, but others having heard this have tried for themselves and found the opposite. I am one of those people, for example. So such an experience can leave them confused and frustrated and perhaps questioning. The publishing of some numbers really helps modellers decide if their wheels would work or not work - but the success or failure of the wheels has nothing to do with OO-SF, which is a track standard. I think the strongest reason for adopting OO-SF is to be able to run code 88 or semi-scale wheels, which do not run well on traditional HO standards. That does not mean that OO-SF runs better than those other track standards, because those track standards were never designed to run those wheels in the first place. Gauge narrowing through turnouts must result in a greater minimum radius for the same wheels used, especially if the turnouts are curved. The same principal applies to gauge widening on normal track - widen the gauge, you can run smaller radii; narrow the gauge, greater radii. This may be of no importance to some, or critically important to others. But it is a fact. (edited in italics) There are a few options for running wheels with a smaller width: have wider flangeways with controlled depths so that narrower wheels run on their flanges. The European NEM standards have this written into their track and wheel standards, for instance. It has been mentioned many times on many forums that a good way to get reliable running of smaller width wheels through traditional wider flangeways is to fill in the bottom of the frogs with small strips of thin metal or plastic to allow for flange running- and some manufacturers make frogs this way so you don't have to modify anything. This isn't new. (edited: additions in italics) use a finer track standard designed for those wheels such as Fine:HO or the UK equivalent DOGA-Fine. Again, not a new idea. use the current HO standard and just have narrower flangeways, which are still within the published standards. I don't know why this isn't discussed much, but I have since found some older threads on the subject, so I am looking into it further. narrow both the flangeway and the track gauge - OO-SF. That's four options, each with their plusses and minuses. What you choose to use is up to you. Is OO-SF better than the other three? I guess it depends upon what is important to the individual concerned. What do I think? My only gripe - my one and only negative - is the inability to find out factual information to help me decide for myself. Too many claims made that, when I go to the trouble of building a turnout and testing, turn out to be false. I feel I have wasted considerable time. And believe me, it is not helpful for some poster to airily claim that I "should" have known such and such, or that this-and-that does not apply, when such claims for OO-SF are made multiple times. "Try it for yourself, you can't go wrong" - well, I did, and it didn't work - for me. Trying to work out why and nail down some actual numbers uncovered the culprit - not every wheelset or wheel standard will work. That is not a drawback for OO-SF, which is a track standard - but it is not helpful to have some wild claims made to the contrary that turn out to be false. (edited: emotive language struck-through, my apologies) I'm glad Martin helped out, he put up some numbers on a OO-SF web page. Now everyone can look and decide for themselves if their wheels will work. My last point - OO-SF will work or not work depending upon engineering, not on your beliefs or motives. Beelzebub can use OO-SF if he wants to. Questioning someone's motives or other such clap trap belongs in a cult, not a hobby.