About how manny Miles can you get out of a set of NGK TR55 plugs before its time to replace them ??? :P

A long time if your not worried about performance a little.

why would they be bad for performance?

If you have a strong ignition, they don't lose power within a year. After a year, i'd replace them. Whether that is required or not, I don't know, but that'* what I would do.


-justin

I replace mine twice a year, but could probably leave them in longer. Gap them at .055"

I didn't know high performance plugs need to be replaced so often. :?

If they are the IX Iridium type, they will last for about 100,000 kms.
It'* not difficult to remove them and check them every year just to analyse condition and gap.
I checked mine after a year and they are perfect.