Minimum Radius Question

I agree with Harry.  Don't risk a disappointment.

.....

Dennis

I agree also.   The mfg usually give pretty accurate specs.   I have an MG J1 2-10-4 that the mfg said should handle 54 inch minimum radius.   I can run it on 52 inch radius but it does not like it.   The curve has to be very smooth, no kinks or sharp spots or the loco derails.

Stick to what the mfg recommends - it will save some later heartbreak.

You could always do something impractical, like run it only on the straights. You could still enjoy the sounds, and see it run a little.

But buying a locomotive that the manufacturer recommends O54 with the hope that it might run on O48 or smaller is extremely risky.

Try to keep it as wide as posible. You never know when you will get bigger engin.

 if you have room use it. I have a mimimum of 072 on my layout. my old layout was 054 and keep me from running the big engins.

 I have a lot of customers that bring engins to run at my house. a lot of them are big.

Thanks fellas! That's good advice. I'll stick to engines that run on 042 or smaller. no sense making a mistake. 

Keep in mind that even the O-72 curves that look wide in comparison to O-31 are still ridiculously sharp for the large locos we run on them. O-72 is proportional to a 20" radius curve in HO which is just a tad wider than the track that comes with a train set. 

For what it is worth, my experience is that the curve rating is pretty much a guarrantee it will work in the most extreme situations of that curve:

- All of my O-54s loco will run on track with any combination of )-54 curves, switches,  back to back curved S sections, etc, and even if the track is perhaps bending up or down lightly as it goes into or out of sloped sections, etc.  Similarly my O-36 rated locos will do the same but on curves, siwtches and esses as sharp as 36."

   But most of my "O-54" locos willactually through straightforward, flat, level 0-48 curves - no switches involved, no back to back or close curves turned in opposite directions, no changes in slope while on the curve. But they trip up on the curved part of switches,esses, slopes, etc.

It all depends on the engine.

I've had engines rated for O72 that would negotiate nothing less. For example, MTH NYC Niagara, P2a boxcab electric, NH EF3 and EP3 electrics, MTH 2-10-4, etc.

Others with wider curve ratings could negotiate O42 curves. For example, Lionel WP 4-8-2 and MTH NKP 2-8-4, etc.

You can't make general statements; you have to test each.

Then, of course, it depends, too, on how smooth your curves are. Sectional track of any make does not go down perfectly without measuring. Always check the diameter of your curves with a tape measure and sight along the rails to make sure nothing is kinked.

Even better -  draw the track centerline on your roadbed first using some sort of trammel/compass. Then fasten down your track following this line.

If your experiences do not seem to match what others have achieved in negotiating curves, check your track.

Jim

I don't like to pick a nit here, but those numbers refer to diameter.

Most folks don't have the kind of room it takes, but my feeling is that a good minimum radius to run scale length equipment would be 96 inches, or sixteen foot diameter.  This is roughly equivalent to 48" minimum radius in HO.

For me, if it wasn't for O-31 tube track and toy length equipment I couldn't even have a three-rail O gauge layout.

Pete

(bold emphasis above mine)
O192, wow!  (I though O120 at 10 foot diameter was a grand curve to strive for!)

As to the HO, don't you mean 18" radius?  That was the standard years ago with train sets.  I recall having some 22" radius curves and then a few 15" radius ones that I used just for a curved siding where I wanted ot be able to park some short rolling stock.

-Dave

No, I meant for HO 48" radius is a preferable minimum for running scale length equipment.  Most modelers simply don't have room for this, although some of the "serious" folks seem to be using 36" minimum.  Don't know if it's still true, but the NMRA minimum for HO used to be 24".  O-120 certainly is a worthy goal to strive for, provided you have the space.

Pete

Even in real life the Railroads have limitations.

The UP had to re-lay a lot of track for the Big Boys to run on.

Both for the weight and the curve minimums.

Once when asked why they don't have a Big Boy in the steam program the response was "We only have 2 turntables left that can turn one and they are only a few miles apart in Wyoming"

I suspect the track and roadbed would have a hard time taking the weight as well.

Remember, that engine is 132 feet 9&7/8" long and weighs 604 TONS before you add coal and water.

The main issue on manufacturers' recommendations has to do with old engines.

If a pre-Fastrack Lionel engine recommends a min 42", back before O36 Fastrack existed, you know they recommended 42" because it wouldn't run on O31 -- 42" was their next size up.

Likewise for an old Lionel recommendation for 54".  You know it won't run well on 42" but you have no data on O48 Fastrack.

Test in these cases, it may work.

  --Joe

0120 nice to have. Isn't that the reason why 3 rail scale locomotives have blind flanges so they can negotiate smaller (all relative) curves i.e. 072, 081 etc. 2 rail O scale needs 10,12 20' diameter curves for the larger type scale steam locomotives.

Thanks for clarifying.  I was basically a kid when doing HO, so I never really touched true scale offerings I suspect, so I dind't have much exposure to that.  I was basically a Blue Box Athearn fan with a bunch of cheap (some cheaper than others) manufacturer's rolling stock mixed in.  I never went beyond some of the half way decent Bachmann steam engines. 

I was essentially playing with toy trains at half the size of O gauge is probably a fair summary!

-Dave