I just got some of IM’s standard 36" wheels for my IHC passenger cars. These wheels are GREAT compared to P2K’s. I was surprised how heavy they are. I definitely want to convert all my cars to these wheels now. My problem…the standard wheel treads are a bit wide. Does anyone have any experience with their semi-scale tread wheels? Just wondering about any kind of tracking/derailing problems I might run into. (using Atlas code 83 track) Any comments good or bad about them?
L:
I don’t think I’d go for any kind of semi-scale wheels unless I was handlaying track. The way I see it, I like running trains better than I like looking at wheels, and narrow wheels can run into trouble in situations that are a bit less than ideal. I had big problems with narrow wheelsets on a Roundhouse 2-6-0, so I put normal RP25 wheels in and the problems all went away.
Now, the finescale people will tell you that if everything is scaled down with tighter flangeways and so forth, you can make exact scale wheels work. The problem is that the extra effort needed makes this a hobby on top of another hobby, and if you keep stacking hobbies you end up with a job.
Summary: Good for a few people to do, fun for a lot of us to see, but most of us are better off with the standard, IMHO. I’d go with the standard-width wheels.
While I don’t use IM (I use Reboxx), I do use the .088" wheel treads, and I DON’T handlay track. Atlas Code 100 flex and Peco switches. I’ve never had a problem with the narrower wheel treads. They look much better, and track just fine. Unless your track is really horrible you won’t have any trouble with the semi-scale wheels. If it is, you’ve got more problems than wheels.
Here’s another vote in favor of the .088 wheels from IM. I have used several sets and will eventually convert all of mine from the standard IM wheels. I use Atlas code 83 and Atlas turnouts. The only time I have a derailment is when I forget to set the turnout properly.
I just wish IM offered the semi-scale wheels in more than a 12 pack.
Tom
THE MOST popular brand of NMRA RP-25 code 100 Flextrack is wider than NMRA specs BECAUSE:.
(1) A marketing design) to allow easier tracking on curves, (2) A holdover from track available 50 -60 years ago, (3) imited to single brand ?
Andy R. care to answer? - What and Why?
my 2 cents
This gets pretty technical pretty fast, but the bottom line is that unless your turnouts have flangeways (and track gauge) at the narrow NMRA limit, you will likely have some wheel drop going through the turnout frog when using code 88 wheels in HO. This can be partially offset with filled in frogs (Atlas, so the wheel rides on the flange and not the tread) or with extremely sharp frog points that stick further into the frog throat (Fast Tracks).
To properly support a wheel through a frog, the wheel tread must be at least twice the width of the flangeway. See the NMRA Standards and RPs for more details. A code 110 wheel has a tread width of .110", which matches well with a NMRA max 0.050" flangeway. The NMRA minimum flangeway is set at .040", which matches the code 88 wheels fairly well. And is why semi-scale wheels are not narrower - protoype tread width is 0.064" in HO.
So why aren’t flangeways set at .040"? Because the check gauge - the distance between the guarding faces of guard and wing rails - plus the flangeways equals the track gauge. Check gauge is determined by the gauging of the wheels and is pretty consistent for almost all your rolling stock. Altering a correctly set check gauge in the track means re-gauging all your wheels! Therefore, the width of the flangeways impacts the track gauge. Fast tracks has a decent video explaining these relationships on their web site.
Why not have your track gauge right at NMRA minimums? Many hand layers and Railway Engineering turnouts do just that. And code 88 wheels (used extensively in HOn3) work quite nicely. The drawback of running minimum gauge through a turnout is that your Big Boy or your 4-8-4 is no longer going to make it through a #4 (or maybe even a #5) turnout. Much of today’s rolling stock depends on gauge widening on curves and lots of lateral motion of the drivers and wheels to make the very sharp minimum radii advertised. The curved portion of an Atlas #4 turnout has a radius of about 22".
Folks:
I suppose the situation I had included various other factors. This wasn’t an IM wheelset, and maybe it was narrower than .088". It was a lightly sprung pony truck on a light engine, running into a switch whose diverging leg was built into a sharp curve. This was a new Snap-Switch, and the stamped points might have been a bit sprung. I fiddled with these, and fiddled with the wheel gauge, and got the loco to derail in different ways, but the wheel change fixed it right away, and being a metal wheelset, I got an extra contact point for free. 
The way I see it, semi-scale isn’t scale, so I’d rather stick with something that can handle suboptimal situations better, since I don’t really want to invest the effort to go full-on Proto:87. I feel the same way about semi-scale magnetic couplers, too.
FW: Interesting info. I want to add that if you handlay using a 3-point track gauge with the single point on the inside rail, you get automatic gauge widening on curves, which is a nice thing.
I guess it won’t hurt to try a dozen and see what happens.
fwright-Thanks for pointing out the wheel drop over the frog problem. I hadn’t thought of that. Atlas turnouts have a pretty bad wheel drop problem anyhow. I’ll have to look at how the standard tread wheels act them.
Love your avatar, Autobus.
Tom
Just a suggestion, Loathar, but you might try the Reboxx sets. They have varying axle lengths to accommodate the various manufacturers’ sideframes. There’s a chart you can use here:
http://www.theoldandwearycarshop.com/Reboxxcharts.html
With “The Tool” journal reamer and these wheelsets, you can get amazingly free-rolling cars. If your LHS doesn’t have them, they can order them.
I use Peco switches, and have had zero wheel-drop/derailment problems with the Reboxx wheelsets. With Atlas switches, I had them all the time with the standard .110" wheels. Upgrading your turnouts is a good move in any case, regardless of the wheels you are running.
I don’t deny your results. I don’t what flangeways Peco uses on their turnouts - I don’t own any. I do know their North American code 83 rail line has finer tolerances than their other track lines. But be aware of what is likely happening with turnouts with the typical 0.050" flangeway.
A long time ago, sprung trucks were highly sought after and prized because the wheels could theoretically equalize and accommodate somewhat rougher track. Many of these were poor implementations, and didn’t have any equalization at all - a wheel would hang in the air passing over a dip in the track because the springs were too stiff. Getting correctly sized springs in trucks to match both the car weight and look reasonably realistic is/was not simple. As a result, sprung trucks have become much rarer than they used to be. Both tight rigid frame trucks and improperly sprung trucks prevent the wheel drop at frogs - the wheel just hangs in the air when not supported by the rail.
Rigid trucks can be made more free-rolling. It is well known in Pinewood Derby (pine cars with plastic wheels) that rigid axles that don’t quite touch all 4 wheels perfectly are faster than softer, 4 wheel contact. Reasonably tight rigid side frames ensure the needle point bears on the proper surface for the best in free rolling. And if one wheel loses contact, it’s no big deal for free rolling ability.
However, these rigid qualities require tighter tolerances in the track to prevent derailments. If a small-flanged wheel is partially hanging, the track vertical tolerances are reduced to about half the flange height, or the whee