Will ThinLine compromise custom saddle fit?

No.

One of the great things about ThinLine is how thin AND effective it is.  If you have a custom-fitted saddle a ThinLine pad will not alter the fit.  ThinLine absorbs impact and reduces movement of the saddle so it works well in conjunction with perfectly fitted saddles.

If you need to balance a saddle that is not custom fitted this is easy, just add the ThinLine shims. You will see them listed as an option under all of our shimmable pads.