glider

The disc can run true even if the wheel is out. The disc is attached to the hub and the wheel through the spokes is also but has to be trued to the hub. If it is noticeably out of true, I would jack up the bike and affix something to the fork that would line up with the rim and turn the wheel slowly to verify if it is out of true and deal with it accordingly. You should also check the spokes periodically for tightness by tapping on them with a wrench or something to see if they all "ring" in the same pitch when you slowly turn the wheel.
You should get the same ring from them all and if you don't, it is a loose spoke and should be taken care of.

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