I cant say for sure about the pinching as the locak mc shop is doing the install but I really doubt it they do tires all day every day...
I called Dennis Kirk Technical assistance and told them that I'm on my second 100/90-18 and my 3rd tube ....
They have suggested and are sending a 90/90-18 and new innertube.
If this one doesnt fit I'm at a total loss?

?