So let's try to answer this question. VHF/UHF signals travel in a straight line from one antenna to another antenna. Line of Sight full stop. They do not follow the Earth in ground wave nor do they get reflected by the ionisphere back to Earth as skywave or "Skip".
There is a formula to calculate the maximum radio distance between two stations. √(2*H1)+√(2*H2)= LOS
Station 1 has an antenna at 60' at home
Station 2 has an antenna at 10' on car
Multiply the heights. H1=120' H2=20'
Find the squares √H1=10.95 √H2=4.47
Add them. For simplicity let's round them up. 11+4.5= 15.5 miles line of sight. Now add any obstructions in between the two antenna and your range is shorter. Leaves on trees, buildings, hills and the like. Most walkie talkies are held at around face level. 5.5' double it 11' root of 11 3.61 miles add this to another walkie talkie and you're looking at a max LOS of 4.22 or 4 1/4 mile range over flat unobstructed terrain. Hill tops will extend it but unless you're going to hike to the top of the hill every time you're using a walkie talkie radio. Expect LESS than 4.25 mile range.
Just hoping these will help you.