Can you put 20 inch rims on a 2002 Cadillac Deville and still have a good ride?

A lot will depend on what kind of tires you get, and what suspension upgrades you make (i.e., better shocks/struts). I will say that a Cadillac will ride pretty well no matter what, but 20" rims I have seen on cars generally lead to more complaints than positives, esp. if you live in an area where flat, non-potholed roads are not common.

just make sure the tires have a nice high sidewall. The handling will suffer a bit, depending on how heavy the wheels are, but my bro has 22" SRTs on his Dodge Ram, and it still rides fine. Now, you'd have a problem if you tried to put on those ridiculous "donk" 30 inchers...

no offence but 20 inch rims suck on any ride the damig your suspension and they make a crappy bounce ride i sugest leaving them stock 4 the best feel

if you want rims go with 18s at the most

Depending on suspension pkg, base, sport, or soft ride. All math regarding tires, suspension ,and brakes should be upgraded