Hi Loran.  Our standard spacer on the JD cat 1700 and later tailpiece provides about 2-3/8" center to center on the teeth at the tightest point if both wheel are in the front hole.

We find that is the best all around spacing for corn and soybeans.  We do have a narrower spacer that we have sold for the previous Curvetine in cotton.

There are tradeoffs in spacing.  An issue is the lateral play in both the row unit tailpiece and the row unit itself. And then there are curves and sideslopes, all of which tend to cause the planter row units to crab a bit.  No vee closing wheel should be directly over the seed.

The new M series Curvetine does offer more adjustability in addition to several other improvements.

As far as down pressure on closing wheels and needing "more" according to the Beck's study, I think we need to be very careful with that.

More often I see too much down pressure on Curvetines rather than too little.

The standard 12" od x 1" wide OEM rubber tire has 4 or 5 sq in of contact area per side or 8-10 sq in of soil contact area per row.  What they were probably seeing is that with this much contact area a lot of pressure is needed in many soil conditions to eliminate air pockets around the seed. I believe that.   The standard Deere and especially the new White tail piece spring put an incredible amount of down force on closing wheels.

Another approach is used with the Curvetine. Two Curvetines per row have only 3 or 4 sq in of contact with the soil at any given time and therefore do not need anywhere near the tail piece down force that the OEM rubber tires do in any given soil condition.

Too much down pressure can make bricks around the seed in some soil conditions.

The way to judge is to dig seed behind the planter: is the seed down in the bottom of the seed slot with good seed to soil contact and no air voids right around the seed?  On the JD 1700 and later tail piece we rarely get out of the lightest spring slot. JD also offers a half rate tail piece spring through dealers parts counters for those in highly tilled or lighter ground.

Note that what ever down pressure is applied to the tail piece tries to unload/lift the row unit and can in fact affect seed depth unless you have a lot of down force on the row unit air  bag, springs etc.

Note in this stiff, wet SE WI clay notilling beans between corn rows this White 6000 planter has the tailpiece spring in the second lightest notch. If he had two Curvetines per row the first notch would be more than adequate even in this tough soil. Look at the seed slot sidewall ahead of the closers

Look at the rubber tire side, look at the Curvetine side, and if you were a seed which side would you rather emerge from?  Two rubber tires and a lot more down pressure would be very harmful to emergence in this condition as well as many others.

I hope this helps.

Jim at Dawn

(One OEM rubber closer (top) + One Curvetine (bottom) in heavy clay notill pic 2.JPG)

(One OEM rubber closer (top) + One Curvetine (bottom) in heavy clay notill pic 3.JPG)

One OEM rubber closer (top) + One Curvetine (bottom) in heavy clay notill pic 2.JPG (91KB - 955 downloads)

One OEM rubber closer (top) + One Curvetine (bottom) in heavy clay notill pic 3.JPG (98KB - 989 downloads)