rim mock up

I built a frame for my d50 and with 16s i have on to roll around it doesnt lay out, my 20s dont have tires but i sat them on pieces of a 2x4 what do you guys use for this will i be alright using the wood i plan on runninng 235/40/20 IF i can

check a tire calculator it gives you the overall diameter and well i think the 40 series is more then 2 inches

thanks man did not know that shit existed lol apparently the size tire i wanna run is 3.7 inch sidewall, so i guess i need a 4x4 eh haha or some damn tires