it is not true—
1. it is false or erroneous:
- It is not true that the future of British bird life is one of depleted numbers.
2. (coll.) it is amazing; it is incredible:
- You may be only thirtysix but you’re so dead old-fashioned it isn’t true.
it is untrue — = it is not true 1:
- It is untrue to say that red wine should be paired with red meat and white wine with fish.
Note: Neither expression correlates in meaning with the phrase out of true—not correctly aligned or adjusted:
- I got on my bike and tried to get going again but … my front wheel was out of true.