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Discussion Starter #1
I really like the look of the six wheel trucks on the newer locomotives. Will these run without problems on 18" radius tracks? I only have room for a 4' x 8' layout and most of the curves in my layout will be 22" radius but there will be a few 18" radius curves, too. Will I be OK with say an SD70?
 

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Short answer... chances are, no, not likely.
It'll be ok on 22"r, but 18" will be dicey.
 

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Individually, even six-drivered steamers have no problems with 18" radius. It's when you add the engine and trailing trucks that things go wrong. It's the length of the frame. On diesels, it's the same problem.

Our models have designed movement two ways in trucks, at least in steamers they do. The trucks pivot, but they also have side-play to help on our layouts' tight curves. I don't believe that diesel trucks have the side-play, and therein lies the huge limitation for six-wheeled trucks on tight curves with long frames.
 

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My two Athearn CN SD40's negotiate 18" curves just fine.....but maybe that's just me.....:eek:hwell:
 

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My two Athearn CN SD40's negotiate 18" curves just fine.....but maybe that's just me.....:eek:hwell:
My Genesis SD75M doesn't play well with anything less than 20" r. above crawl speed, and it looks awful doing it.
 

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Athearn SD40-2's are designed work on tight turns. They were introduced in 1984 and the tolerances are pretty loose so they should make it without too much difficulty. Newer 6 axle locos are built to tighter tolerances and are much less likely to be able to make an 18" curve.

Most should work on 22", but if you're buying a state-of-the-art high-end loco it's never a bad idea to ask for folks experience with a specific loco. The good news is that there's alot of Athearn Blue-Box stock out there in good shape.

That said, it sounds like you like the look of a Big Safety cab modern loco. I don't know about the SD70 (Athern's version is "Genesis" series), but maybe Blue Box C44-9W and AC4400CW might work on 18" curves. Definitely don't buy one on my suggestion, though perhaps someone else can give you better advice.

One other thing to consider is that perhaps you can re-gauge the center axle on each truck to have a bit more play.

Lastly, there are some 4-Axle Safety Cab locos that have much of the modern "look". GP60M perhaps? There are a number of makers. Walthers had an 8-40BW until recently and Atlas makes it too. I'd still advise asking for personal experience, but if you're buying a new-production locomotive, I think sticking to a 4 axle is best. Lastly, a shorter 4 axle loco will look much better around small curves than a longer 6 axle.
 

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On my 5x10 layout, there aren't any mainline curves below 22", (the majority are 24 to ~28") and inner loops are 18 to 20".
My 'late model' 6-axle diesels don't see anything tighter than 20" r... Switchers, Geeps and RS11's only.
 

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Some boxes on 6 axle engines will say 18" minimum radius, suggested 22" radius. The problem with 18" radius the back of the engine will hang over the track pulling the coupler of the railcar and forcing the trucks to derail. You would have to find a car that will have enough swing in the coupler and the trucks back far enough that there's no torque on them.
 

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Discussion Starter #9
Thanks all for your reply. I stopped by my LHS today and he also suggested that as a new HO hobbyist and with my restriction to a 4 x 8 layout that I should stick with an eight wheel loco. I do like the look of the modern safety cab locos and besides the GP60M he showed me some GP38's and GP40's. I liked them all! So I'll just stick with an 8 wheel loco until I gain more experience.
 

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Wise decision.
Alas, quality Geeps are in short supply in these parts.
 

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I have an old blue box dash 9 and it will run on 18"radius curves but its not very graceful. I would stick to 4 axle diesels if you want it to be smooth as glass but if youre running at speed it will do ok. somewhere around 50% throttle was the sweet spot for smooth running and not derailing. hope this helps and I agree with eilif on the tolerance comment. I have a couple proto e8 locomotives that will NOT make it through anything tighter than 20 radius
 

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This is an Athearn RTR GP50 I have. You might like it.
It's a fairly modern design, and may fit the genre of what you're looking for.
Athearn RTR stuff is very well detailed, and won't perform open-wallet surgery on you.

ATH_RTR_GP50.jpg
 

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Thanks all for your reply. I stopped by my LHS today and he also suggested that as a new HO hobbyist and with my restriction to a 4 x 8 layout that I should stick with an eight wheel loco. I do like the look of the modern safety cab locos and besides the GP60M he showed me some GP38's and GP40's. I liked them all! So I'll just stick with an 8 wheel loco until I gain more experience.
That sounds wise, and clearly you're getting the railroading bug!

Even though they were made in the 60s and 70s GPs are still extremely common today in yards. Here on the west side of Chicago I see them nearly every day.

As for layout size have you considered a 5x9? It's the size of a ping pong table and you can fit 27" and 24" loops on it.
 

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There are "older-design" 6-axle engines that will work with 18".

Examples:
SD7
SD9
SD35
RSD4/5

These engines have shorter overall wheelbases and will handle 18" radius well enough. You -might- need to use Kadee couplers with a longer shank so they don't bind.

But "more recent" engines, the newer, bigger, longer ones?
Doubtful. They just need "more room"...
 

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Discussion Starter #15
Thanks everyone.... I now have some really good ideas to use when I search the internet to find some of the locomotives that were suggested. Really good information. Thanks again to all.....:smilie_daumenpos: JOHN
 

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I have a member at my club who insisted that modern ho scale locomotive would NOT run on 18"R curves, I have a portable layout I'm building and the radii are 23", 21" and 18". I took the ends with the track to the club and a variety of engines including Athearn and Kato SD70ace and SD90/43mac's, all the loco's ran well on the 18"R curves except an old Rivarossi challenger, it did NOT like anything under 21"R.
They look not perfect but will run on the curves, manufacturers would cut themselves out of a good segment of the market if there loco's DIDN'T run on 18"R curves thus affecting the bottom line.
Don
 

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Looks aside anything is possible. A little carving and my Bachman DD40 AX takes 15" ers AT SPEED with 20 cars behind it over and over. Baldwin Shark too 15" no problem Athern Genesis SD 45 goes thru the 15" unmodified with no trouble...js
 

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I know the Bachmann catalog and website state that the HO-scale Bachmann SD40-2s will work on 18" radius curves. I also know Mehano's old Alco C628 six-axle locomotives work really well on 18" radius curves, even through the turnouts!

This Alco C628 was sold by quite a few North American model train manufacturers/distributors, such as AHM, IHC, Life-Like and Model Power. (Life-Like even billed the C628 as a more "premium"-quality locomotive, compared to their other base-line engines using the cheaper Power-Drive pancake motors.) Even the later TYCO "Railroad Empire II" set used this locomotive, and it was definitely a better runner than TYCO's own Alco Super 630 diesel.
 

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I just built a 4x4 sheet of plywood for a friends son and he has a blue box dash 9 that he was wanting to run and it won’t handle the curves like mine will. So there must be a tolerance variation between mine and his. The board has 18” curves on it
 
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