DD40x minamum radius

[911mickeyh]

Whats the smallest or standard curve radius for this little monster?

[r0bert]

I wouldn't go under 22 inch, with wide path for overhang, 26-28 should really be the min.  it will operate on 18 but you probally won't be able to couple any cars behind it.

[chuff_n_puff]

It kind of depends on what brand type you have. I have both, an Athearn DD40 and a Spectrum DD40AX, both which have been converted to DCC with sound. The DD40AX is a dual motor and about an inch longer than the DD40, which is a single motor unit. The Spectrum has a tighter turning radius than the shorter DD40, due to the way the trucks are made. They have about double the swivel to them. I have all 33" radius curves and the Athearn stills tries to bind up, if I don't keep the speed up. But the Bachmann will creap around flawlessly. If you have not already purchased one and want one of higher value, get the Bachmann Spectrum DD40AX. Now you will have to pay attention as Bachmann made both! They had a DD40 plain Bachmann single motor in a white box and a DD40AX Spectrum dual motor in a black box. They have been out of production for years, but you can still find a few on eBay. They all are a trick to convert to DCC, if you are not familiar with this procedure. If you have a professional do it for you, it could cost you way more than the train, if you count the parts! Hope this helps you.