A spectral index n _ { s } \lesssim 0.95 appears to be a generic prediction of racetrack inflation models .
Reducing a general racetrack model to a single-field inflation model with a simple potential , we obtain an analytic expression for the spectral index , which explains this result .
By considering the limits of validity of the derivation , possible ways to achieve higher values of the spectral index are described , although these require further fine-tuning of the potential .