First a question: On the XX1 Cassette, what is the centerline distance between the cogs, not the spacer thickness, but the centerline distance between cogs?

Why?

My understanding is that a 170 hub has a chain line of 66mm. A Middleburn crank with a 145 BB spindle = a 66mm chain line.

From the Surly tire geometry chart a Bud on a Clownshoe is 119mm wide, lets call it 120mm. half that = 60, or just enough for 6mm of chain clearance with the above set-up. So, Buds on 100's with a 170 hub and 145 spindle...single speed works.

Now, if one were to run a 2x set-up with the inner ring set at the middle position of a 3x, and the other in the outer position, and then offsetting the rear dropouts the distance of 2,3, or 4 cogs...? Another question is how far to the right can the outer ring be pushed?

To keep things simple, (?) lets assume that the above required spider has the same 58 or 64mm BCD for both rings, could they be run side by side without interference with the other chain ring? (By the way, using fingers to move the chain over.) If a larger BCD for the outer is desired...I make the assumption...I find the gear spread of the XX1 sufficient in itself.

So, in effect you still have same 11 gears, but are using two rings up front to reduce the swing of the chain at the rear. The inner ring would not access x number of the smaller cogs and the outer ring would not access the same number of the inner cogs, hopefully providing a means to reduce the Q up front.

Hopefully, I have described this well enough to be understandable...any more and I might loose myself. (Well, lets not say any more.)

We all have read...yeah, you can do that...but be prepared to loose a couple of gears...usually at the loss of the bottom cogs.

Why loose any cogs...can the cat be skinned through the above method...without the usual increase in Q?

Of course, the frame would have to be built with this in mind, and I understand that CS length can make a difference.

And lastly, is there any merit to the above approach to make it worthwhile?

If so, maybe something closer to those 6" tires, while we are at it...?

So, back to the question at the top...what is the centerline distance between the cogs on a XX1 cassette? Knowing that...maybe make some scale drawings...

Rip it apart if need be...how we learn.