I mounted my CB antenna on my tire carrier but didn't try to rig a ground wire yet. I get a SWR of 1.1 on channel 1 and 1.5 on channel 40. Is there any benefit with a good SWR if I ground?

 

Good grounding will always improve performance. you can have a good swr without a good ground. But you might just have a good ground right now. Hard to tell for sure with seeing it.

 

I added a ground to mine because there was no continuity between the bracket and the body. Adding one fixed that. My 2¢.

 

Under lab conditions, low SWR with no ground to the antenna really doesn't tell you much. The real test is how far can you talk on the open road and on the trail?

 

lol that's no test. You know how many variables on second by second basis there are that effect transmit and receive?

 

The average Jeeper is not a EE and really doesn't care how variables there may be, on a second by second basis, for any given transmission. What they do care about is, when they say "hello" on their cb, does someone say "hello" back. And that was my point, how does it work on the trail and the road where it really counts.

 

I was in the same position (Good SWR when mounted on the spare carrier). I went ahead and added a ground for the hell of it. It's easy, and it surely won't hurt anything.

 

If your mount is painted or powder coated there is a VERY good possibility you don't a ground.

 

Your SWR is fine. The only problem with mounting on tailgate or tire carrier is the hinges are not the best at keeping a solid ground. So today you have 1:1 but it could potentially change down the road. The "ground" you want is for RF, not electrical. If you start experiencing SWR issues start by properly grounding or bonding the tailgate to the rest of the vehicle with a braided ground strap.

Good info here:
h t t p://www.k0bg.com/bonding.html