What are Zertz inserts on a Specialized Vita?

[Hi Ho Silver]

...snip

Not sure why folks are feeling the Zertz bikes as less responsive. No reason they should feel that way. Personal preference I suppose.

I'm always surprised by the remark that the Zertz equipped bikes are less responsive. I think maybe people are inappropriately equating "responsiveness" with tactile and/or auditory feedback, because I find that my Ruby accelerates well (er, as well as this old engine can power it along) and responds immediately to steering inputs.