You have a bunch of bad things going on.
1. You have a metric butt ton of open edges (see attached screen shot)
2. In order for the bend to produce a perfect circle all the edges must be perfectly vertical.
(1a) To see how this is borking you look at the attached screen shot of your model before I tweaked it.
Look at the vertical edges you can see they are all wonky especially where they are not closed.
(1b) now look at a section of the tweaked model before I applied the bend. All the vertical edges on the left side are now aligned vertically. I simply selected them all All except one, slid them to the left a bit then held the v-key and middle mouse gestured over the vert I did not select and all the verts are now aligned to the unselected verts x coordinate.
I left all the open edges and did not align any of the other inner verts.
But now that inside edge is a straight line so if I bend it by approximately PI (-3.14159....) you can see in screen shot (2) that the inner part of the tire is now close to a perfect circle. I added a nurbs circle so you can see that the inside now lines up and is circular.
Now the outer edge of the tire is still off because of all the inside edges that were not vertically aligned and also open.
To fix this properly you should (1) close all the open edges and then align all the egdes vertically from what will be the inside of the tire to the outside. The tread area is going to be off a bit but will be very hard to align but it should end up close enough that when merged it will be unnoticeable.
You see the offset error you are getting is cumulative so the more of the vertical edges that you align the closer the entire thing will be to circular in the end. That is why you can skip tying to straighten the vertical edges in the tread area.
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675
Last edited by ctbram; 07-08-2012 at 01:58 AM.
