As a HAM since the fifties and a commercial 2-way shop owner for 15 years dealing in low band VHF (39mhz) and CB as well as high band and UHF, here is some info.
If you have a properly grounded vehicle, cable length is not a factor, in fact at low power CB shorter lenghth is an advantage. You are attempting to keep the resistance of the cable balanced with the radio and antenna to get maximume power transfer.
Grounding: Must include grounding the antenna to the roof, if you are using complex mounts with open ground brain from the coax, an additional short length of copper braid, flattened and attached between the antenna ground screwed with star washer into the roof and sealed with silicone or other water tight seal will help. Body ground, you also should ground the body metal under the vehicle to the frame using the copper braid and weather sealed.
Last but not least, ground the negative post of the battery to the frame in the same manner. The regulare vehicle electrical ground is not all that solid and needs this extra solid ground. In all cases wire brush the surface area and clean with alcohol. On more help is to ground the tail pipe to the frame. It can cause electric noise.
Power, it is alway best to run a "home run" positive and negative cable * or 10 gauge from the batter to the radio. If you hook up to any other vehicle electric you will get noise. Vehicle electrical systems have very poor RF suppression. Check with your local sound installer. They always connect direct for noise suppression and heavy power need.
Tuning, the previous post is correct, the antenna must be in use condition when tuned. One thing many people forget when tuneing especially when the mount is over the drivers door, close the door.
One last thought, the Firestick is a great antenna because you can tune it easily and retune it any time you add something to the roof a9lights, bars etc). The rule for antennas is the longer the better. The 4' Firestick is the best comprimise for a low profile, foldable antenna.
In radio, every little thing adds up to major difference in results. You can short cut it if you don't care about the extra distance or clarity.
As a cop and emergency worker for many years I always go the extra step for the added security in that one situation when you REALLY need the extra.
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