This is a non lifted EZGO Marathon golf cart. It looks like 18" tires is stock and many forums say 20" fit, but do they rub on these old EZGO Marathons? Do I need a spacer, should I get one to play it safe, what size?
The EZGO Marathon uses shorter front springs than a TXT and there isn't a lot of clearance on the brake pedal when turning left especially with older/weaker springs. Chances are good 20" tires are going to rub your brake pedal when making left turns and braking at the same time and wheel spacers won't help. You can make some 1" or 2" spacers to go between the springs and the axle like the old block lift kits to raise the front end if they do rub. Or use EZGO TXT springs to move the axle forward.
Turn left and look under the cart and see how much clearance you have with someone sitting in the cart pressing the brake pedal with the stock 18" tires. With 20" tires you'll lose about one inch on the clearance.