Would the trunk/back seats fit 4 x 20" wheels?
 

I need to pick up my old wheels from a shop

They're staggered 20" wheels (tire + rim)

255/30/20
225/35/20

Would they fit at all? Can I fit at least 2 in one trip? or am I better off renting a bigger car/asking a friend for help?

Should fit easy. If anything, one in the trunk, two in the backseat, and one in the front seat. They fit a lot more than you'd think lol

Thanks

I should probably cover them well so I don't get the front seat dirty :D

Should be fine. With your backseats down you can fit 3 between the trunk and backseat back and one in the front, or put a wheel on top of the one on the backseat. I've done it with my 18"s a few times.

Wasn’t the whole concept that a complete set of track wheels will fit inside?

Doesn’t matter what size the wheels are, up to a 24” or so.

Yeah I get a full set of wheels, jack, stands, tools, cooler, chairs, easy-up. The only time I had to put anything in the front seat is when I went down to CA and had to bring luggage. Prolly could have got that in that back too with more careful packing.