Track radius query.

[geejbee]

Hello.

The box for my J15 0-6-0 says the minimum radius is 438 which I believe is 2nd radius. The same applies to my 4-6-2 Tornado which is easy to understand but I can't see why this is an issue for the little 0-6-0. I have to say that I have used it on the small section of my layout which uses 1st radius without any obvious problem but do wonder if in so doing I am putting a strain on the running gear etc. Could someone advise me about this please.

[Going Spare]

The ability of a loco to negotiate a curve is mainly governed by the driving wheels wheelbase.  Although the J15 is a smaller loco than the A1, its driving wheels are spaced quite widely so overall wheelbase length may not be much different between the two classes.  It is possible, but not advisable, that with care, Tornado may also be ok on radius 1.

[geejbee]

Thanks Going Spare, but what criteria do Hornby use to establish what the minimum track radius recommendation will be.

[Going Spare]

That is a question, with, I suspect, a complex calculation that only Hornby can answer.  Others here with more technical knowledge than mine may be able to offer you an explanation.  In times gone by, the centre driving wheels had either no flange at all or reduced depth flanges to permit any loco to run round 1st radius curves but with all now having full depth flanges, the limited lateral movement of the wheels necessitates a greater radius of track curvature.

[Chrissaf]

I should imagine that the answer is its an arbitrary 'Marketing Decision'. Marketing have decided that in these more modern times that Radius 2 should be considered the minimum. Thus the designer, designs the wheel geometry such that a minimum Radius 2 can be achieved. I doubt that it is any more complicated than that.

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As G.S says above, the radius will likely be defined by the lateral play that is allowed in the wheel-sets, based upon the wheel size, wheel base and wheel configuration. It would be a compromise between enough lateral movement to meet the minimum Radius 2 requirement versus not so much lateral movement that binding of wheel drive and coupling rods (if fitted) occurs.

[geejbee]

Thanks, that makes sense to me, so hopefully I won't damage anything by running the J15 on the 1st radius.

[Going Spare]

Make sure the loco is not struggling.  If it is, you will be putting additional strain on the motor and drive, and causing additional wear in the wheels, coupling rods and axle bearings.  

[geejbee]

Understood thank you. In fact it glides along beautifully.

[LCDR]

Back in the "bad old days" the centre driving wheel of a model was flangeless to reduce friction on the 13" radius curves common in those days. More recently a flange was put on but narrower that the others, remember flanges used to be both deep and thick. With finer wheel standards it has been found possible to negotiate 17" curves (438mm) but 15" curves are less certain, and bogies and pony trucks and some tender couplings on modern locos and rolling stock  just cannot make it. 

 

A minimum curve for a BR Standard steam loco in real life is 4 chains or 88 yards, 80ish metres, to be negotiated at walking pace. In OO scale that is just over a metre, say 3' 6" radius. And most models scream round radius 2 at a scale 120 mph!

[96RAF]

If you think about it an 0-6-0 is likely the same driver wheelbase (distance between the first and last axles) as a Pacific 4-6-2, as the latter probably has a flying (flangless) trailing truck and a steerable pony (leading) bogie. The important bit, the six wheels in the middle, has to negotiate the same radius on either loco type.

[bruce_johnson]

I have a Blue Streak train set from the 1980s. It has a oval of Radius 1. I rediscovered it about 10 years ago. The first new train I got was a basic 0-4-0 which of course ran on the track no problem. My next Loco was the Railroad Cock o' the North. 

Interestingly the Hornby high detail Version had a minimum radias criteria, but the Railroad version, which I believe uses the same running gear, does not. I have run my P2 on first radias turns and it manages it no problem. The only problem I have found is if I go too fast the front bogie jumps the rails, but this happens on all tracks. All 8 driving wheels are flanged, and so far I have not yet found it's limit in pulling power (more than can be said for my 9Fs).

[Rana Temporia]

I have a Jouef 2-10-0 (or 1-5-0) that goes around first radius curves with no problem whatsoever and as it picks up from all wheels it will do it at a crawl. Their first radius was round 12.75" and their second approximately the same as Hornby 1st. I know they are HO and not OO but it's still pretty impressive. 

 

The comparison between a tank wheelbase and a pacific is interesting and something I only realised fairly recently.