Longer Antenna?

Hopefully this is the right spot.

I did some googling, and I can't find anything, so hopefully someone here can help me out.

I'm looking for a longer antenna for my truck. I'm also hoping to move the mount to the bed of the truck, on one of the rails or something. If anyone knows where I can get a longer and better antenna, and a relocation kit, I'm all ears. I'm not really familiar with radio stuff, and this doesn't appear to be a popular mod, so any help is appreciated.

Edit: I'm talking about an fm radio antenna. Trying to improve reception while driving in the mountains.

 

Actually antennas are cut for the frequency they're intended to receive so using one to short or too long could be detrimental by changing the impedance of the RF system. Here's a calculator to find out what length you need, also I think automotive head units use 75 ohm cable.

 

That's good to know. I figured bigger would be better but I guess not. Hopefully a relocation and maybe a signal booster will help

 

Well bigger might be better but you never mentioned what your antenna is for?

Regardless of the band you are trying to receive and building on the good info already given the only time that bigger is better is if it is bigger in a resonant multiple length of what you are trying to tune.

What are you trying to improve reception on exactly?

 

Oops! I'm trying to improve my fm radio reception. I don't have satellite or a cb or anything fancy, just want to listen to the regular radio as much as possible in the mountains.