Grill the sausages 5-8 minutes, until browned. Slice into ¼ inch rounds and place in a large salad bowl.
Brush the ears of corn generously with olive oil and season with salt and pepper. Grill, 15-20 minutes, turning occasionally, until they just begin to brown. Remove from heat and set aside to cool. Once cool enough to handle, cut the kernels from the cobs into the bowl.
Add the tomatoes, black beans and cilantro to the bowl.
In a small bowl, whisk together the cumin, sour cream, sugar and lime juice. While whisking slowly drizzle in the 1/2 cup olive oil. Pour over the salad and toss to combine. Served chilled or at room temperature.