You need an "SWR Meter" to tune an aerial in correctly .....although if you look at the "signal strength" meter on your rig [if it has one] .....if the signal is 80% or over you wont be far out.
IIRC ...The length of your new cable could [ ] affect the "ground plain [plane?]" of your aerial,and affect the SWR [Standing Wave Reading] ....my advice is do a search on Google or Wikipedia.
btw .....I dunno if SWR meters are still available .....I used to use one back in the 70's .....but I lost interest in CB radios when the FM system was introduced into the UK [was it in 1981 or 82????]

10-10
T.

Why not just park closer to the people you're talking to?

or buy a mobile phone

Bit tricky when you dont know where they are......'cos you've just lost them on a convoy through an unfamiliar town.
And I dunno about you ......but I find it hard work shouting to the guy in the next 2CV at speeds of over 40mph ....

'Cos you can only phone one person at a time ....so that makes it tricky when theres three or more of you in a group.
Not to mention the fact that we dont all have contracts with millions of minutes per month ...specifically, 'cos [unlike most of the younger generation] ....we cant live without a mobi. phone permanently stuck to our ear.
Oh,and FWIU .....its illegal to talk on a mobile phone whilst driving..... IIRC,CB radio isnt subject to the same law.

T.

hi terry i used to be into cb years ago, good fun , met lots of people including ladies
i had one in the car but i bought a full lengh aerial --27 and a half ? i stole a long scaffold pole and bolted it to a barn where i used to live
the aeriel on the top
i could contact anywhere in the world including american truckers
something to do with sunspots

btw terry i thought cb was finished/dead ? i,d get another one if its still active