Why is the curve of the Wankel engine rotor flatter than a Reuleaux triangle?

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I’m not an expert mathematician so for a long time I just assumed that the rotor of a Wankel engine was in the shape of a Reuleaux triangle. My assumption was wrong. Did Wankel start from a Reuleaux triangle and then flattened the curves to better contain the hot gasses or to change the friction issues or …?