When it comes to choosing a truck size for your skateboard size 8, it ultimately comes down to personal preference. Typically, a 7.75-8.25" skateboard works best with a 5.0" truck, whereas an 8.25" board should be used with a 5.25" truck. Ultimately, it is up to you to decide what truck size feels most comfortable as you skate. Before you make a final decision, you may wish to take your board to a skate shop and ask to test out both sizes to determine which works best.