I have a conventional old-ish mountain bike front wheel - 26", 32 hole, disc brake, 100 mm over locknuts. I've been using it for road riding for years and have never trued it, but recently borrowed a wheel truing stand, so thought i would give it a look.
It appears to be reasonably true laterally and radially - a millimetre or less, i would say. But when i align the stand's indicator with the non-drive-side rim (with the brake rotor), then flip the wheel round so it points at the drive side, there is a 7 mm gap. If i understand correctly, that means the wheel is 3.5 mm out of dish (or however you say it).
Could it have come from the factory like that? If not, could it have drifted that amount in use, without losing its true in other ways? Is it a problem that it's that far out? Or have i just misunderstood how wheels should work?
I am tempted to correct it, now i have it in the stand (and while i am waiting for some new inner tubes to arrive). Would i be wasting my time?