20's on Ranger

hey everyone, i am gonna be buying some 20's soon for my 2WD 93 4 Litre Ranger. just wondering if anyone has come across any problems while swaping for bigger rims and tires. and if anyone knows the max width of a tire you can put under a ranger that would be great. also, is there any way to make the speedometer still read correctly since it doesnt have the diognostics plug? thanks alot.