Road movement by tanks in Memoir '44
Armor can move 4 hexes and still battle at full strength.

From p. 5 of the Terrain Pack rules:


  Armor may move 4 hexes on a road and still battle.


The main rulebook makes it clear that Armor's battle strength is unaffected by its movement (p. 9):


  [Armor] always combats at 3 dice.


P. 15-16 of the FAQ has a concise summary of the effects of Roads on all units, which might be of interest if you have questions about other units. 


  Armor - 4 hexes and battle