This isn't advice to just having a car but friends in general.

I always feel free to offer if I know it's not too far off the way, I always never mind them asking... However if they expect it or you think they'll be angry if you say no or if you don't offer it then you should reconsider your friendship in general.

Before I had a car here, I never expected anyone to give me a ride and the few times I asked I tried to make it as easy on them as possible (ie going somewhere closer to get picked up and being prompt) when my friends said no I said no problem I completely understand (I didn't care what reason or no reason they give, as the most important thing was I never felt they owed me anything)