89mm. K&N sports air filter with great effect
K&N sports filters are always top quality, they deliver more air to the engine and make sure you get more upwind, acceleration and a really nice sound. This filter is a CLAMP-ON air filter, ie it can be clamped on a round tube that is 89mm. in outer diameter. Since the material it covers is made of rubber, it can extend well beyond the 89mm.
You can advantageously buy a K&N filter cleaning kit - Gives your air filter a longer life and keeps the effect up.