I am in the process of buying a new bike and am having problems with identifying the wall type on the bontrager rims on the Trek 4300 and 3900 bikes, i.e. are they single or double walled. The 3900 has Bontrager 550s and the 4300 has the Camino rims. I have gleaned enough info to know that I need to get enough bike that I don't outgrow it's capabilites too soon. I have been adviced to go with double walled rims for durability and to reduce the need for truing. I come from an offroad motorcycle background where rims are always double walled minimum. Any help will be greatly appreciated.