The best surfing beach on mainland Sabah is located quite literally on the very tip of Borneo - the northern most point of Borneo island - in the Malaysian district of Kudat. The drive from Kota Kinabalu city to Kudat takes about 3 hours. Once at the tip you have several choices for accommodations varying from very basic longhouse-style dorms to comfortable twin-bed rooms with aircon and ensuite bathrooms.
The swells are generated from the South China Sea, and the most consistent swells will occur between November and January during the Northeast Monsoon (winds predominantly coming from the Northeast).
Being more exposed that many other beaches in Sabah, the beaches at the tip of Borneo will catch swells better and the waves breaking on the tip of Borneo beach tend to be 20% bigger than on the beaches near Kota Kinabalu.
Throughout the year their may be waves created by localised storms on a random basis. During the month of August might be especially big due to the typhoon season in the Philippines.