A modification of the calendar spread, the ratio calendar spread trade have more contracts sold than bought.
With more long contracts, this removes the constraint on one end of the profitability range, thereby allowing for unlimited profit if the stock price makes a large move in the appropriate direction.
Fewer near month contracts are sold than the number purchased of distant month contracts.
With call, this has the effect of opening the upper end of the risk graph for unlimited profit if the stock moves higher.
With puts, this has the effect of opening the lower end of the risk graph for unlimited profit if the stock price moves lower.
Ratios such as 3:2 or 4:3 are good ones to consider.