the proper way to make a kalimotxo is using a 1:1 ratio, which means fifty percent red wine and fifty percent coca-cola. to prepare it properly, fill a tall glass with plenty of ice, pour in about 150ml of red wine, and top it up with 150ml of regular cola. give it a very gentle stir with a spoon so you do not ruin the carbonation
as far as the wine goes, you definitely should not use a high quality bottle for this. a very basic, dry red table wine from the supermarket is the standard choice because the sweet soda completely masks the finer tasting notes anyway. it is super easy to make and actually turns out quite refreshing on a warm day imo