It all depends on how much extra room you have in your helmet, or if you'd be willing to grab a helmet that's a size larger. That's the only concern you will have - the fact that dreads do make your head-size a bit larger. Especially as time goes on, naps grow fatter as no hair really falls out of them like with normal hair, but there are a lot of Knotty kids that are helmet-wearers and haven't run into a problem that we’ve heard of. You’ll be fine!