Do I need to retune SWR if I change antenna angle?

It wouldn't hurt to check SWR again. I am just wondering why you are tilting a 4ft whip to begin with. Normally, (according to the Wilson antenna engineer that I spoke with) mobile antennas are supposed to be straight up and down. Tilting them distorts the radiation pattern. If tilting the antenna brings the SWR ratio down, then you have other problems, most likely lack of ground plane.

 

Your SWR will go up with a 4ft antenna on the Cascadia the more vertical you go. If you tilt one past about 15 -17 degrees though, you start losing performance, even if you do lower the SWR, which it does. There is no way that I've found to get good performance out of anything less than a 5ft antenna, a top loaded one ( and longer is better, 7ft still is under 13'6" overall) on the Cascadia.

 

Longer is better. Any top loaded fiberglass antenna will do. I use a Skip Shooter -7ft. Looks like it has a nail stuck in the top of it. Some use the 7ft Fire Stick. I've got a old Radio Shack SWR meter I carry with me. Most of the time I can predict what the SWR will be since I drive the same model trucks all the time (I slip seat so different truck every week) but every now and then I get a surprise! So I check mine every time I hook up a radio. These newer CBs will blow the finals quicker than the old ones if your SWR is too high so it is a good idea to always know what it is when you hook your radio to it.