What are smooth tubes?

[GENIIGTS]

Hello everyone. I ordered K&N filter's and I read that you should put smooth tubes on as well. What are they?

 

[Marv S]

The stock tubes (except GT-2 and ACR) have ridges that can cause turbulence as the air passes through. The smooth tubes, either do it yourself or buy from any Viper vendor (Roe, HMS, etc) depending on your preferred color & style, let the air travel with less restriction. Cheap way to get a few more ponies.