Most nosedives happen at around 19-20 mph, I usually dont drive faster than 13-15.
Also depends on the weight, if you are tall&heavy, you should drive even slower.
Also nosedives happen if you just plain accelerate on flat ground with flat stance, I prefer to “carve” and alternate weight between sides of the wheel. That way you can decrease power required to move (because of decreased contact area and decreased rolling resistance)