Or ...... get a new car?
Seriously though, I can get a mudguard bike into several cars I have use of, including an Astra hatchback (not a big car), by removing just the front wheel of the bike and folding the back seats down. - there's often a way, even if it includes pushing the passenger seat forward with small cars.
It's a Renault Modus, which is just about perfect for my non-cycling needs. I've not had a chance to try yet, but I think I might possibly just get the bike in vertically with the back wheel in place if I pop the saddle and fiddle with the bars. That's actually preferable to dropping the back wheel because I've got a hub motor (mumble, mutter, heresy - yes I know!).
I still need a solution for the for the front wheel, because it might well only fit with the forks reversed. I'm running 40mm tyres and might go even fatter, so Raceblades are out, and I want full mudflap-to-the-floor protection. I had a mad idea about making a guard out of some flat springy material, sliding it into a fitting under the fork crown, an email pulling it into shape with tension cords, but a readymade solution would be easier.